3. 5th international conference on earthquake geotecnical engieneering
TRANSCRIPT
r5th INTERNATIONAL CONFERENCE ON EARTHQUAKE GEOTECHNICAL ENGINEERING January 10-13 2011 Santiagomiddot Chile
51CEGE 3
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATION221 ORIENTEO TO SEISMIC ANALYSIS
An-Bin HUANG 1 Wen-Jong CHANG 2
ABSTRACT
A sound site characterization program for the purpose of geotechnical seismic analysis should provide adequate information regarding soil stratigraphy groundwater conditions geostatic stresses and stress bistory characteristics middotof hydraulic conductivities undrained monotonic and cyc1ic strength as well as deformation and damping characteristics assessed in the strain range of interest The purpose of the paper is to describe sorne ofthe recent developments in geotechnical and geophysical site charactlrization methods as they relate to seismic response and liquefaction potential analyses The currently available semi-empirical field-based as well as the critical state based methods for the evaluation ofundrained cyc1ic strength using the site characterization test results are reviewed Because the interpretation of in situ index tests for soil liquefaction potential analysis remains empirical it is imperative to calibrate these empirical methods for local soils especially for the case of intermediate soils such as sands with fines The critical state approach appears promising as Iacutet has a sound theoretical basis and circumvents many ofthe problems associated with empirical interpretation of in situ tests however it needs refinement especially in the context of inferring soil cyc1ic strength from CPT
Keywords in situ test geophysical exploration sampling liquefaction soil deformability state parameter
INTRODUCTION
Seismic analysis in Geotechnical Engmeering can cover a wide range of activities In order to analyze the response of a soil deposit to a seismic event in a rational manner the required information should inc1ude (Jamiolkowski et al 1995)
Soil stratigraphy Groundwater conditions Geostatic stresses and stress history Characteristics ofhydraulic conductivities Undrained monotonic and cyc1ic strength Deformation and damping characteristics assessed in the strain range of interest
Researchers have generally agreed that geotechnical and geophysical site characterization methods are complementary to each other The site characterization can include in situ (mechanical and geophysical) tests and laboratory tests on natural soil samples Near-surface geophysical tests based on sound theoretical basis offer geotechnical engineers the opportunities to characterize the
Professor Department of Civil Engineering National Chiao Tung University e-mail abhuangmailnctuedutw
Assistant Professor Department of Civil Engineering National Cheng Kung University e-mail wjchangmailnckuedutw
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sites materials and processes with high efficiency due to the nonintrusive nature and ability to perform the same measurement in the laboratory and field (Stokoe and Santamarina 2000) Soil stratigraphy stress states stress history as well as deformation and damping characteristics may be revealed by these geophysical test methods
Field geophysical exploration encompasses gravity magnetic seismic reslstlvlty and electromagnetic measurements The applicability of selective noninvasive techniques to site characterizations are summarized in NRC (2000) and the engineering parameters inferred from various geophysical methods are summarized in Stokoe and Santamarina (2000) In geotechnical earthquake engineering seismic methods are dominant because they directly measure the mechanical properties including material stiffness and damping in elastic or small strain level which are required in designs and ana1yses of geotechnical systems subjected to both monotonic and seismic loadings Many of the seismic-based geophysica1 exploration methods are nonintrusive cfnd can cover a large area which makes them cost effective in profiling the spatia1 distribution of engineering parameters and applicable in hard-to-sample soi1s Furthermore seismic methods can be performed both in the field and laboratory samp1es which provides quantitative assessments of sample disturbance (Landon et al 2007) degree of saturation (Allen et al 1980) and microstructure of soils (eg cementation and anisotropy) (Belloti et al 1996)
Taking good quality samples for cohesive soils is significantly easier than for cohesionless or granular soi1s Traditionally undisturbed granular soil samples have been taken by ground freezing and dry coring This method can be prohibitively expensive and usually is used for critical or research projects Successes have been reported by Huang and Huang (2007) and Huang (2009) in the use of Laval and gel-push sampler to take samples in granular soils with reasonable quality By avoiding ground freezing these methods are significant1y more practica These new sampling technique developments make laboratory tests on undisturbed soil samp1es much more feasible With the advent ofloeal strain and bender element measurement capabilities valuable information on deformation and damping characteristics as well as undrained strength of natural soils can be obtained from monotonic or cyclic laboratory shearing tests
Because of the difficulties involved in undisturbed sampling in situ testing plays a much more important role in characterizing granular soil deposits especially for the case of seismic analysis Mayne et al (2009) identified over thirty types of available in situ test methods The use of in situ tests has proven significant in the characterization of geomaterials in several aspects (1) they can be done relatively quickly as compared with laboratory tests (2) results are available immediately (3) large number of data is obtained and (4) vertical and lateral variability can be assessed Seismic piezo-cone penetration (SCPTU) and seismic ftat dilatometer tests (SDMT) (Marchetti et al 2008) are two commonly used full-displacement penetration tests but with added capability of shear wave velocity measurements similar to those of downhole geophysical tests SCPTU and SDMT can also be used to infer groundwater conditions and characteristics ofhydraulic conductivities ofthe tested soils by monitoring the decay ofpenetration induced excess pore water pressure These hybrid and multi-functional test devices are especially useful in meeting the demands for seismic analysis related site characterization An important disadvantage for penetration tests is that t~ey usually create complicated boundary conditions and make rigorous interpretation ofthe test results rather difficult For granular soils the consideration of potentia1 seismic ftow failure or liquefaction further complicates the content ofthe analysis Correlations between in situ test results and soi1 cyclic strength have been proposed for the assessment of liquefaction potential of granular soils following the simpIified procedure (Youd et al 2001) The approach is based on fieId observations of the performance of sand deposits that did or did not liquefy in previous seismic events A set of data points of earthquake induced cyclic shear stress versus in situ test results are pIotted first The correlation curve is established based on a borderline that separates
64
GEOTtcHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANAlYSIS
the data points that correspond to liquefaction and no liquefaction Jefferies and Been (2006) offered an altemative way to evaluate soilliquefaction potential via state parameter From theoretical point of view this is a more desirable approach as compared to the simplified procedure because of the strong correlation between state parameter and sand dilatancy To take full advantage of this approach however a reliable means to infer state parameter from in situ tests would be required
The aim ofthis paper is to summarize sorne ofthe recent developments in geotechnical and geophysical site characterization techniques as they relate to seismic response and liquefaction potential analyses Subjects to be described in the paper inelude
Geophysical site characterization Defonnation and damping characteristics Undrained cyelic strength from in situ index tests Undisturbed sampling in granular soils
The state parameter approach to evaluate soilliquefaction
GEOPHYSICAL SI TE CHARACTERIZATION
Field seismic testing techniques involve monitoring the partiele motions of different modes of propagation from disturbance induced by active or passive sources Active sources release energy from a mechanical device or explosion to induce stress waves propagating in solid medium and a passive source used the background noise as the excitation The modes ofpropagation ofien used are two body waves (eg P-wave and S-wave) propagating within the mass of medium and the Rayleigh wave (R-wave) existing near the surface Complexity of stress wave field which depicts temporal and spatial variations of stress waves within a medium depends on source characteristics soil properties and geometry and will reflect on recorded seismic records Because recorded seismic data contain aH the infonnation from the complicated wave field all seismic testing techniques involve enhance or separation of different modes of propagation using different testing layouts and signal processing techniques
In situ stress-wave based techniques gain more attentions in geotechnical earthquake engineering because they can provide infonnation oflayer thickness and dynamic soil properties (eg modulus and damping) at small strain level which are major parameters in perfonning site specific ground response evaluations and dynamic soil structure interaction analyses Most stress-wave based methods measure the propagating velocities from travel time in time domain or by spectrum analysis in frequency domain The maximum shear modulus (GmaJ shear wave propagatin~ veloci~~d strcas state of soils can be related by
Gmax =pv =CsJF(e)(ra(rb (1) a a
where p is mass density es na and nb are material constants F(e) is a void ratio function Da and q are the principal effective stress in the direction ofwave propagation and partiele motion respectively and Pa is the atmosphere pressure Incorporating Gmax from field testing (Gmaxfield) into normalized modulus reduction curve from laboratory tests which is the ratio of shear strain at different shear strain level (G(Yab) divided by the maximum shear modulus in the laboratory(Gmaxab) the field modulus at different shear strain level (G(Y)fiel) can be inferred by
G( ) (G(Y)zab)Gy jield = G maxjield (2)
maxlab
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A brief review of stress-wave based geophysical characterization methods is presented below Futher details can be found in Stokoe and Santamarina (2000) Sheriff and Geldart (1995) and Richart et al (1970)
Intrusive seismic methods Intrusive seismic methods require boreholes to install the source and receivers and the wave velocities are evaluated by measuring travel time ofthe specific travel path from the source to the receiver In geotechnical field cornmon types of intrusive methods are Crosshole tests downhole and seismic cone penetration tests and suspension P-S logging
Crosshole method The crosshole method is a time-of-travel measurement where the source and receivers are placed at the same depth in adjacent boreholes Standard layout of crosshole methods are shown in Figure 1 and the testing details can be found in ASTM standard D4228 (ASTM) The crosshole seismic testing requires an in-hole source capable of generating both P-wave and S-wave propagating hofizontally The receivers must be able to record particle motions in 3 orthogonal directions in arder to measure the P SH and SV wave velocities Advantages of crosshole method include high resolution for testing materials capability of render a tomographic image of the cross section by inclined ray paths as well as measurements of P SH and SV wave velocities at the same depth The major disadvantage ofthe crosshole method is the time and cost of preparing the boreholes (Stokoe and Santamarina 2000)
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Figure 1 Layout of crosshole seismic testing (ASTM)
66
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
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SCPT Al DEPTH In
(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
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68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
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Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
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]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
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p VP1
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Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
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Fig L Typical geological struaure of a sedimentarybasin
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GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
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Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
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ll lO 1O~ 0 1
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Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
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103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATION221 ORIENTEO TO SEISMIC ANALYSIS
An-Bin HUANG 1 Wen-Jong CHANG 2
ABSTRACT
A sound site characterization program for the purpose of geotechnical seismic analysis should provide adequate information regarding soil stratigraphy groundwater conditions geostatic stresses and stress bistory characteristics middotof hydraulic conductivities undrained monotonic and cyc1ic strength as well as deformation and damping characteristics assessed in the strain range of interest The purpose of the paper is to describe sorne ofthe recent developments in geotechnical and geophysical site charactlrization methods as they relate to seismic response and liquefaction potential analyses The currently available semi-empirical field-based as well as the critical state based methods for the evaluation ofundrained cyc1ic strength using the site characterization test results are reviewed Because the interpretation of in situ index tests for soil liquefaction potential analysis remains empirical it is imperative to calibrate these empirical methods for local soils especially for the case of intermediate soils such as sands with fines The critical state approach appears promising as Iacutet has a sound theoretical basis and circumvents many ofthe problems associated with empirical interpretation of in situ tests however it needs refinement especially in the context of inferring soil cyc1ic strength from CPT
Keywords in situ test geophysical exploration sampling liquefaction soil deformability state parameter
INTRODUCTION
Seismic analysis in Geotechnical Engmeering can cover a wide range of activities In order to analyze the response of a soil deposit to a seismic event in a rational manner the required information should inc1ude (Jamiolkowski et al 1995)
Soil stratigraphy Groundwater conditions Geostatic stresses and stress history Characteristics ofhydraulic conductivities Undrained monotonic and cyc1ic strength Deformation and damping characteristics assessed in the strain range of interest
Researchers have generally agreed that geotechnical and geophysical site characterization methods are complementary to each other The site characterization can include in situ (mechanical and geophysical) tests and laboratory tests on natural soil samples Near-surface geophysical tests based on sound theoretical basis offer geotechnical engineers the opportunities to characterize the
Professor Department of Civil Engineering National Chiao Tung University e-mail abhuangmailnctuedutw
Assistant Professor Department of Civil Engineering National Cheng Kung University e-mail wjchangmailnckuedutw
t
rjiexcl
2
63
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sites materials and processes with high efficiency due to the nonintrusive nature and ability to perform the same measurement in the laboratory and field (Stokoe and Santamarina 2000) Soil stratigraphy stress states stress history as well as deformation and damping characteristics may be revealed by these geophysical test methods
Field geophysical exploration encompasses gravity magnetic seismic reslstlvlty and electromagnetic measurements The applicability of selective noninvasive techniques to site characterizations are summarized in NRC (2000) and the engineering parameters inferred from various geophysical methods are summarized in Stokoe and Santamarina (2000) In geotechnical earthquake engineering seismic methods are dominant because they directly measure the mechanical properties including material stiffness and damping in elastic or small strain level which are required in designs and ana1yses of geotechnical systems subjected to both monotonic and seismic loadings Many of the seismic-based geophysica1 exploration methods are nonintrusive cfnd can cover a large area which makes them cost effective in profiling the spatia1 distribution of engineering parameters and applicable in hard-to-sample soi1s Furthermore seismic methods can be performed both in the field and laboratory samp1es which provides quantitative assessments of sample disturbance (Landon et al 2007) degree of saturation (Allen et al 1980) and microstructure of soils (eg cementation and anisotropy) (Belloti et al 1996)
Taking good quality samples for cohesive soils is significantly easier than for cohesionless or granular soi1s Traditionally undisturbed granular soil samples have been taken by ground freezing and dry coring This method can be prohibitively expensive and usually is used for critical or research projects Successes have been reported by Huang and Huang (2007) and Huang (2009) in the use of Laval and gel-push sampler to take samples in granular soils with reasonable quality By avoiding ground freezing these methods are significant1y more practica These new sampling technique developments make laboratory tests on undisturbed soil samp1es much more feasible With the advent ofloeal strain and bender element measurement capabilities valuable information on deformation and damping characteristics as well as undrained strength of natural soils can be obtained from monotonic or cyclic laboratory shearing tests
Because of the difficulties involved in undisturbed sampling in situ testing plays a much more important role in characterizing granular soil deposits especially for the case of seismic analysis Mayne et al (2009) identified over thirty types of available in situ test methods The use of in situ tests has proven significant in the characterization of geomaterials in several aspects (1) they can be done relatively quickly as compared with laboratory tests (2) results are available immediately (3) large number of data is obtained and (4) vertical and lateral variability can be assessed Seismic piezo-cone penetration (SCPTU) and seismic ftat dilatometer tests (SDMT) (Marchetti et al 2008) are two commonly used full-displacement penetration tests but with added capability of shear wave velocity measurements similar to those of downhole geophysical tests SCPTU and SDMT can also be used to infer groundwater conditions and characteristics ofhydraulic conductivities ofthe tested soils by monitoring the decay ofpenetration induced excess pore water pressure These hybrid and multi-functional test devices are especially useful in meeting the demands for seismic analysis related site characterization An important disadvantage for penetration tests is that t~ey usually create complicated boundary conditions and make rigorous interpretation ofthe test results rather difficult For granular soils the consideration of potentia1 seismic ftow failure or liquefaction further complicates the content ofthe analysis Correlations between in situ test results and soi1 cyclic strength have been proposed for the assessment of liquefaction potential of granular soils following the simpIified procedure (Youd et al 2001) The approach is based on fieId observations of the performance of sand deposits that did or did not liquefy in previous seismic events A set of data points of earthquake induced cyclic shear stress versus in situ test results are pIotted first The correlation curve is established based on a borderline that separates
64
GEOTtcHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANAlYSIS
the data points that correspond to liquefaction and no liquefaction Jefferies and Been (2006) offered an altemative way to evaluate soilliquefaction potential via state parameter From theoretical point of view this is a more desirable approach as compared to the simplified procedure because of the strong correlation between state parameter and sand dilatancy To take full advantage of this approach however a reliable means to infer state parameter from in situ tests would be required
The aim ofthis paper is to summarize sorne ofthe recent developments in geotechnical and geophysical site characterization techniques as they relate to seismic response and liquefaction potential analyses Subjects to be described in the paper inelude
Geophysical site characterization Defonnation and damping characteristics Undrained cyelic strength from in situ index tests Undisturbed sampling in granular soils
The state parameter approach to evaluate soilliquefaction
GEOPHYSICAL SI TE CHARACTERIZATION
Field seismic testing techniques involve monitoring the partiele motions of different modes of propagation from disturbance induced by active or passive sources Active sources release energy from a mechanical device or explosion to induce stress waves propagating in solid medium and a passive source used the background noise as the excitation The modes ofpropagation ofien used are two body waves (eg P-wave and S-wave) propagating within the mass of medium and the Rayleigh wave (R-wave) existing near the surface Complexity of stress wave field which depicts temporal and spatial variations of stress waves within a medium depends on source characteristics soil properties and geometry and will reflect on recorded seismic records Because recorded seismic data contain aH the infonnation from the complicated wave field all seismic testing techniques involve enhance or separation of different modes of propagation using different testing layouts and signal processing techniques
In situ stress-wave based techniques gain more attentions in geotechnical earthquake engineering because they can provide infonnation oflayer thickness and dynamic soil properties (eg modulus and damping) at small strain level which are major parameters in perfonning site specific ground response evaluations and dynamic soil structure interaction analyses Most stress-wave based methods measure the propagating velocities from travel time in time domain or by spectrum analysis in frequency domain The maximum shear modulus (GmaJ shear wave propagatin~ veloci~~d strcas state of soils can be related by
Gmax =pv =CsJF(e)(ra(rb (1) a a
where p is mass density es na and nb are material constants F(e) is a void ratio function Da and q are the principal effective stress in the direction ofwave propagation and partiele motion respectively and Pa is the atmosphere pressure Incorporating Gmax from field testing (Gmaxfield) into normalized modulus reduction curve from laboratory tests which is the ratio of shear strain at different shear strain level (G(Yab) divided by the maximum shear modulus in the laboratory(Gmaxab) the field modulus at different shear strain level (G(Y)fiel) can be inferred by
G( ) (G(Y)zab)Gy jield = G maxjield (2)
maxlab
65
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A brief review of stress-wave based geophysical characterization methods is presented below Futher details can be found in Stokoe and Santamarina (2000) Sheriff and Geldart (1995) and Richart et al (1970)
Intrusive seismic methods Intrusive seismic methods require boreholes to install the source and receivers and the wave velocities are evaluated by measuring travel time ofthe specific travel path from the source to the receiver In geotechnical field cornmon types of intrusive methods are Crosshole tests downhole and seismic cone penetration tests and suspension P-S logging
Crosshole method The crosshole method is a time-of-travel measurement where the source and receivers are placed at the same depth in adjacent boreholes Standard layout of crosshole methods are shown in Figure 1 and the testing details can be found in ASTM standard D4228 (ASTM) The crosshole seismic testing requires an in-hole source capable of generating both P-wave and S-wave propagating hofizontally The receivers must be able to record particle motions in 3 orthogonal directions in arder to measure the P SH and SV wave velocities Advantages of crosshole method include high resolution for testing materials capability of render a tomographic image of the cross section by inclined ray paths as well as measurements of P SH and SV wave velocities at the same depth The major disadvantage ofthe crosshole method is the time and cost of preparing the boreholes (Stokoe and Santamarina 2000)
fIlteiexclrsolJrcc eorchulp ~ _ iexcl ~ ~leo es ~
~ - ---- ---- - 0 I 3 et~cs I 3 oaeters IC ~
(10 feet) (10 reet)
Sei~lc Recoder
Seilt Recerveriexcl Source
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Figure 1 Layout of crosshole seismic testing (ASTM)
66
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
~
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(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
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68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
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Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
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~shy I 1
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o
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lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
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o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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01 02 03 04 O 00002 00004 00006 00008 0001
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(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
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SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
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Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
jiexcliquestshy
sites materials and processes with high efficiency due to the nonintrusive nature and ability to perform the same measurement in the laboratory and field (Stokoe and Santamarina 2000) Soil stratigraphy stress states stress history as well as deformation and damping characteristics may be revealed by these geophysical test methods
Field geophysical exploration encompasses gravity magnetic seismic reslstlvlty and electromagnetic measurements The applicability of selective noninvasive techniques to site characterizations are summarized in NRC (2000) and the engineering parameters inferred from various geophysical methods are summarized in Stokoe and Santamarina (2000) In geotechnical earthquake engineering seismic methods are dominant because they directly measure the mechanical properties including material stiffness and damping in elastic or small strain level which are required in designs and ana1yses of geotechnical systems subjected to both monotonic and seismic loadings Many of the seismic-based geophysica1 exploration methods are nonintrusive cfnd can cover a large area which makes them cost effective in profiling the spatia1 distribution of engineering parameters and applicable in hard-to-sample soi1s Furthermore seismic methods can be performed both in the field and laboratory samp1es which provides quantitative assessments of sample disturbance (Landon et al 2007) degree of saturation (Allen et al 1980) and microstructure of soils (eg cementation and anisotropy) (Belloti et al 1996)
Taking good quality samples for cohesive soils is significantly easier than for cohesionless or granular soi1s Traditionally undisturbed granular soil samples have been taken by ground freezing and dry coring This method can be prohibitively expensive and usually is used for critical or research projects Successes have been reported by Huang and Huang (2007) and Huang (2009) in the use of Laval and gel-push sampler to take samples in granular soils with reasonable quality By avoiding ground freezing these methods are significant1y more practica These new sampling technique developments make laboratory tests on undisturbed soil samp1es much more feasible With the advent ofloeal strain and bender element measurement capabilities valuable information on deformation and damping characteristics as well as undrained strength of natural soils can be obtained from monotonic or cyclic laboratory shearing tests
Because of the difficulties involved in undisturbed sampling in situ testing plays a much more important role in characterizing granular soil deposits especially for the case of seismic analysis Mayne et al (2009) identified over thirty types of available in situ test methods The use of in situ tests has proven significant in the characterization of geomaterials in several aspects (1) they can be done relatively quickly as compared with laboratory tests (2) results are available immediately (3) large number of data is obtained and (4) vertical and lateral variability can be assessed Seismic piezo-cone penetration (SCPTU) and seismic ftat dilatometer tests (SDMT) (Marchetti et al 2008) are two commonly used full-displacement penetration tests but with added capability of shear wave velocity measurements similar to those of downhole geophysical tests SCPTU and SDMT can also be used to infer groundwater conditions and characteristics ofhydraulic conductivities ofthe tested soils by monitoring the decay ofpenetration induced excess pore water pressure These hybrid and multi-functional test devices are especially useful in meeting the demands for seismic analysis related site characterization An important disadvantage for penetration tests is that t~ey usually create complicated boundary conditions and make rigorous interpretation ofthe test results rather difficult For granular soils the consideration of potentia1 seismic ftow failure or liquefaction further complicates the content ofthe analysis Correlations between in situ test results and soi1 cyclic strength have been proposed for the assessment of liquefaction potential of granular soils following the simpIified procedure (Youd et al 2001) The approach is based on fieId observations of the performance of sand deposits that did or did not liquefy in previous seismic events A set of data points of earthquake induced cyclic shear stress versus in situ test results are pIotted first The correlation curve is established based on a borderline that separates
64
GEOTtcHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANAlYSIS
the data points that correspond to liquefaction and no liquefaction Jefferies and Been (2006) offered an altemative way to evaluate soilliquefaction potential via state parameter From theoretical point of view this is a more desirable approach as compared to the simplified procedure because of the strong correlation between state parameter and sand dilatancy To take full advantage of this approach however a reliable means to infer state parameter from in situ tests would be required
The aim ofthis paper is to summarize sorne ofthe recent developments in geotechnical and geophysical site characterization techniques as they relate to seismic response and liquefaction potential analyses Subjects to be described in the paper inelude
Geophysical site characterization Defonnation and damping characteristics Undrained cyelic strength from in situ index tests Undisturbed sampling in granular soils
The state parameter approach to evaluate soilliquefaction
GEOPHYSICAL SI TE CHARACTERIZATION
Field seismic testing techniques involve monitoring the partiele motions of different modes of propagation from disturbance induced by active or passive sources Active sources release energy from a mechanical device or explosion to induce stress waves propagating in solid medium and a passive source used the background noise as the excitation The modes ofpropagation ofien used are two body waves (eg P-wave and S-wave) propagating within the mass of medium and the Rayleigh wave (R-wave) existing near the surface Complexity of stress wave field which depicts temporal and spatial variations of stress waves within a medium depends on source characteristics soil properties and geometry and will reflect on recorded seismic records Because recorded seismic data contain aH the infonnation from the complicated wave field all seismic testing techniques involve enhance or separation of different modes of propagation using different testing layouts and signal processing techniques
In situ stress-wave based techniques gain more attentions in geotechnical earthquake engineering because they can provide infonnation oflayer thickness and dynamic soil properties (eg modulus and damping) at small strain level which are major parameters in perfonning site specific ground response evaluations and dynamic soil structure interaction analyses Most stress-wave based methods measure the propagating velocities from travel time in time domain or by spectrum analysis in frequency domain The maximum shear modulus (GmaJ shear wave propagatin~ veloci~~d strcas state of soils can be related by
Gmax =pv =CsJF(e)(ra(rb (1) a a
where p is mass density es na and nb are material constants F(e) is a void ratio function Da and q are the principal effective stress in the direction ofwave propagation and partiele motion respectively and Pa is the atmosphere pressure Incorporating Gmax from field testing (Gmaxfield) into normalized modulus reduction curve from laboratory tests which is the ratio of shear strain at different shear strain level (G(Yab) divided by the maximum shear modulus in the laboratory(Gmaxab) the field modulus at different shear strain level (G(Y)fiel) can be inferred by
G( ) (G(Y)zab)Gy jield = G maxjield (2)
maxlab
65
--
)amp1
l~
ltb 1 e-n f~01 hiexcl- =~smiddot (emiddot~)iacutet1 11 coi Efigil l~)ir-g
A brief review of stress-wave based geophysical characterization methods is presented below Futher details can be found in Stokoe and Santamarina (2000) Sheriff and Geldart (1995) and Richart et al (1970)
Intrusive seismic methods Intrusive seismic methods require boreholes to install the source and receivers and the wave velocities are evaluated by measuring travel time ofthe specific travel path from the source to the receiver In geotechnical field cornmon types of intrusive methods are Crosshole tests downhole and seismic cone penetration tests and suspension P-S logging
Crosshole method The crosshole method is a time-of-travel measurement where the source and receivers are placed at the same depth in adjacent boreholes Standard layout of crosshole methods are shown in Figure 1 and the testing details can be found in ASTM standard D4228 (ASTM) The crosshole seismic testing requires an in-hole source capable of generating both P-wave and S-wave propagating hofizontally The receivers must be able to record particle motions in 3 orthogonal directions in arder to measure the P SH and SV wave velocities Advantages of crosshole method include high resolution for testing materials capability of render a tomographic image of the cross section by inclined ray paths as well as measurements of P SH and SV wave velocities at the same depth The major disadvantage ofthe crosshole method is the time and cost of preparing the boreholes (Stokoe and Santamarina 2000)
fIlteiexclrsolJrcc eorchulp ~ _ iexcl ~ ~leo es ~
~ - ---- ---- - 0 I 3 et~cs I 3 oaeters IC ~
(10 feet) (10 reet)
Sei~lc Recoder
Seilt Recerveriexcl Source
Cltloing
GrQut
Figure 1 Layout of crosshole seismic testing (ASTM)
66
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
~
AXIS OF SCPT HEAR BEAM
SHEAR EEAU
EC~MRS
DI
ASSUMED TRAVEL PATHS Or SElSUIC WAVES FROM SHEAR
SCPT AT DEP1H 01 9EAM TO SEISMOMElERS IN SCPT BOOY AT DEPTHS DI ANO 0201
ASlNC Rour
SCPT Al DEPTH In
(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
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Figure 3 Setup of suspension P-S logger (from GEOVision)
68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
-15 1 = (~~
-201-1-~-
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Velocity msec 500 1000 1500 2000
00
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69
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Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
i~btNJWt D_ -- _
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Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
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iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
1-D Svaloclty (Vs) PrcfU6
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21__ ~_----+-_J~_ shy 811 middott 1la
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otr1tt (ni)
20 laquoJ ~I) so 1CUacute Q ~imltrt1~~~
~
S
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ergt(nriexcl~)
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73
80 120 160 200
o---1-r-----L----L-j
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sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
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Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
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Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
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Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTtcHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANAlYSIS
the data points that correspond to liquefaction and no liquefaction Jefferies and Been (2006) offered an altemative way to evaluate soilliquefaction potential via state parameter From theoretical point of view this is a more desirable approach as compared to the simplified procedure because of the strong correlation between state parameter and sand dilatancy To take full advantage of this approach however a reliable means to infer state parameter from in situ tests would be required
The aim ofthis paper is to summarize sorne ofthe recent developments in geotechnical and geophysical site characterization techniques as they relate to seismic response and liquefaction potential analyses Subjects to be described in the paper inelude
Geophysical site characterization Defonnation and damping characteristics Undrained cyelic strength from in situ index tests Undisturbed sampling in granular soils
The state parameter approach to evaluate soilliquefaction
GEOPHYSICAL SI TE CHARACTERIZATION
Field seismic testing techniques involve monitoring the partiele motions of different modes of propagation from disturbance induced by active or passive sources Active sources release energy from a mechanical device or explosion to induce stress waves propagating in solid medium and a passive source used the background noise as the excitation The modes ofpropagation ofien used are two body waves (eg P-wave and S-wave) propagating within the mass of medium and the Rayleigh wave (R-wave) existing near the surface Complexity of stress wave field which depicts temporal and spatial variations of stress waves within a medium depends on source characteristics soil properties and geometry and will reflect on recorded seismic records Because recorded seismic data contain aH the infonnation from the complicated wave field all seismic testing techniques involve enhance or separation of different modes of propagation using different testing layouts and signal processing techniques
In situ stress-wave based techniques gain more attentions in geotechnical earthquake engineering because they can provide infonnation oflayer thickness and dynamic soil properties (eg modulus and damping) at small strain level which are major parameters in perfonning site specific ground response evaluations and dynamic soil structure interaction analyses Most stress-wave based methods measure the propagating velocities from travel time in time domain or by spectrum analysis in frequency domain The maximum shear modulus (GmaJ shear wave propagatin~ veloci~~d strcas state of soils can be related by
Gmax =pv =CsJF(e)(ra(rb (1) a a
where p is mass density es na and nb are material constants F(e) is a void ratio function Da and q are the principal effective stress in the direction ofwave propagation and partiele motion respectively and Pa is the atmosphere pressure Incorporating Gmax from field testing (Gmaxfield) into normalized modulus reduction curve from laboratory tests which is the ratio of shear strain at different shear strain level (G(Yab) divided by the maximum shear modulus in the laboratory(Gmaxab) the field modulus at different shear strain level (G(Y)fiel) can be inferred by
G( ) (G(Y)zab)Gy jield = G maxjield (2)
maxlab
65
--
)amp1
l~
ltb 1 e-n f~01 hiexcl- =~smiddot (emiddot~)iacutet1 11 coi Efigil l~)ir-g
A brief review of stress-wave based geophysical characterization methods is presented below Futher details can be found in Stokoe and Santamarina (2000) Sheriff and Geldart (1995) and Richart et al (1970)
Intrusive seismic methods Intrusive seismic methods require boreholes to install the source and receivers and the wave velocities are evaluated by measuring travel time ofthe specific travel path from the source to the receiver In geotechnical field cornmon types of intrusive methods are Crosshole tests downhole and seismic cone penetration tests and suspension P-S logging
Crosshole method The crosshole method is a time-of-travel measurement where the source and receivers are placed at the same depth in adjacent boreholes Standard layout of crosshole methods are shown in Figure 1 and the testing details can be found in ASTM standard D4228 (ASTM) The crosshole seismic testing requires an in-hole source capable of generating both P-wave and S-wave propagating hofizontally The receivers must be able to record particle motions in 3 orthogonal directions in arder to measure the P SH and SV wave velocities Advantages of crosshole method include high resolution for testing materials capability of render a tomographic image of the cross section by inclined ray paths as well as measurements of P SH and SV wave velocities at the same depth The major disadvantage ofthe crosshole method is the time and cost of preparing the boreholes (Stokoe and Santamarina 2000)
fIlteiexclrsolJrcc eorchulp ~ _ iexcl ~ ~leo es ~
~ - ---- ---- - 0 I 3 et~cs I 3 oaeters IC ~
(10 feet) (10 reet)
Sei~lc Recoder
Seilt Recerveriexcl Source
Cltloing
GrQut
Figure 1 Layout of crosshole seismic testing (ASTM)
66
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
~
AXIS OF SCPT HEAR BEAM
SHEAR EEAU
EC~MRS
DI
ASSUMED TRAVEL PATHS Or SElSUIC WAVES FROM SHEAR
SCPT AT DEP1H 01 9EAM TO SEISMOMElERS IN SCPT BOOY AT DEPTHS DI ANO 0201
ASlNC Rour
SCPT Al DEPTH In
(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
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illuacutet lo~jork ~ CCiexcl-r
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~ OYDPS-170 ~ LoggeriReccfder
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Ji k~ Uwer (R2) ReceIacuteIIE ~
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rrioj point of R eceIacutellers Q~m
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fl r-~ J oint Deplh reference localion 10r S- R 1 anatysis mid point of 314 m S- R 1 s padng10 m flexible
Is olaion Cylinder I I107 m 37 mJoint
Combined Sh and P-lAlaVe SOlJrce (S)
Soorce Drver 105m
Wlght 1~
lip
Overal Lenglh ~ 58 m
Nct to Scae
Figure 3 Setup of suspension P-S logger (from GEOVision)
68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
-15 1 = (~~
-201-1-~-
-25 t== ==~-~~~ ~ 8 -
f301 3~ -35
-40 1 ~
~~ -45 t=b=======3~ii~j~~lQf2= ~- -50 1 =~
-55~~ -60~
O 10 20 30 40 O 10 20 40
Time (ms) Time (ms)
Figure 4 Time histories for S-wave velocity profiling in southern Taiwan
Velocity msec 500 1000 1500 2000
00
101 Ii 1(
I E t~ Irc 30 1 iexcl 1 t
40 1 J 1 1 )
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Figure 5 P- and S-waves profiles from suspension logger
~lt
69
)jh Hnoicl Cc~middotmiddot
Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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el f ~ 0 1(b) ntilde
6 _LI
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Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
i~btNJWt D_ -- _
O-1m
n-2m
0-
o bull
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Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
~ shy-~ 11~
iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
1-D Svaloclty (Vs) PrcfU6
S-Vli1hxlty~)~riexclII~)
29) ~(J iexclro 1CCjI)= j F
1 ltshy
21__ ~_----+-_J~_ shy 811 middott 1la
J =shyo a
~f -- -j _+- _ -+- iexclf
lO
MultfChannel Record
otr1tt (ni)
20 laquoJ ~I) so 1CUacute Q ~imltrt1~~~
~
S
g fij~~7 LI Ii olI_
lrllltv~m~sect bull tI tl~ fh
ergt(nriexcl~)
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A
73
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
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A brief review of stress-wave based geophysical characterization methods is presented below Futher details can be found in Stokoe and Santamarina (2000) Sheriff and Geldart (1995) and Richart et al (1970)
Intrusive seismic methods Intrusive seismic methods require boreholes to install the source and receivers and the wave velocities are evaluated by measuring travel time ofthe specific travel path from the source to the receiver In geotechnical field cornmon types of intrusive methods are Crosshole tests downhole and seismic cone penetration tests and suspension P-S logging
Crosshole method The crosshole method is a time-of-travel measurement where the source and receivers are placed at the same depth in adjacent boreholes Standard layout of crosshole methods are shown in Figure 1 and the testing details can be found in ASTM standard D4228 (ASTM) The crosshole seismic testing requires an in-hole source capable of generating both P-wave and S-wave propagating hofizontally The receivers must be able to record particle motions in 3 orthogonal directions in arder to measure the P SH and SV wave velocities Advantages of crosshole method include high resolution for testing materials capability of render a tomographic image of the cross section by inclined ray paths as well as measurements of P SH and SV wave velocities at the same depth The major disadvantage ofthe crosshole method is the time and cost of preparing the boreholes (Stokoe and Santamarina 2000)
fIlteiexclrsolJrcc eorchulp ~ _ iexcl ~ ~leo es ~
~ - ---- ---- - 0 I 3 et~cs I 3 oaeters IC ~
(10 feet) (10 reet)
Sei~lc Recoder
Seilt Recerveriexcl Source
Cltloing
GrQut
Figure 1 Layout of crosshole seismic testing (ASTM)
66
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
~
AXIS OF SCPT HEAR BEAM
SHEAR EEAU
EC~MRS
DI
ASSUMED TRAVEL PATHS Or SElSUIC WAVES FROM SHEAR
SCPT AT DEP1H 01 9EAM TO SEISMOMElERS IN SCPT BOOY AT DEPTHS DI ANO 0201
ASlNC Rour
SCPT Al DEPTH In
(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
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illuacutet lo~jork ~ CCiexcl-r
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~ OYDPS-170 ~ LoggeriReccfder
Cable Head lJ
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Combined Sh and P-lAlaVe SOlJrce (S)
Soorce Drver 105m
Wlght 1~
lip
Overal Lenglh ~ 58 m
Nct to Scae
Figure 3 Setup of suspension P-S logger (from GEOVision)
68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
-15 1 = (~~
-201-1-~-
-25 t== ==~-~~~ ~ 8 -
f301 3~ -35
-40 1 ~
~~ -45 t=b=======3~ii~j~~lQf2= ~- -50 1 =~
-55~~ -60~
O 10 20 30 40 O 10 20 40
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Figure 4 Time histories for S-wave velocity profiling in southern Taiwan
Velocity msec 500 1000 1500 2000
00
101 Ii 1(
I E t~ Irc 30 1 iexcl 1 t
40 1 J 1 1 )
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Figure 5 P- and S-waves profiles from suspension logger
~lt
69
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Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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el f ~ 0 1(b) ntilde
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Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
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Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
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72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
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Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
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otr1tt (ni)
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~
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ergt(nriexcl~)
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73
80 120 160 200
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5 -Silly sand (SM)
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- Q
o o o
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o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
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o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
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~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Downhole method and SCPT In the downhole method travel times of shortest travel path between a source on the surface and two receivers at selected depths in a borehole are measured Standard layout of a downhole method is shown in Figure 2 and the testing details can be found in ASTM standard D7400 (ASTM) The average wave velocity between the two receivers is evaluated by
v = (L2 - L1) (T - Tiexcl) (3)
in which L and T are distance and travel time from source to receiver i shown in Figuer 2 The seismic cone penetration test (SCPT) (Campanella et al 1986) is similar to the downhole seismic test with motion sensors integrated in the cone for travel time measurement The advantage of downhole test is that only one borehole is required and the major disadvantage is that more source energy is required for deep measurements
~
AXIS OF SCPT HEAR BEAM
SHEAR EEAU
EC~MRS
DI
ASSUMED TRAVEL PATHS Or SElSUIC WAVES FROM SHEAR
SCPT AT DEP1H 01 9EAM TO SEISMOMElERS IN SCPT BOOY AT DEPTHS DI ANO 0201
ASlNC Rour
SCPT Al DEPTH In
(a) downhole test in cased borehole (b) Seismic cone penetration test
Figure 2 Schematic of downhole seismic test and SCPT (ASTM)
P-S logging Welllogging or borehole logging has long history in petroleum engineering Logging tools can be lowered into borehole to produce the profile ofmaterial properties The suspension P-S logging method is a relatively new method of measuring P- and S-wave velocity profiles of soils (Nigbor and Imai 1994) and is probab1y the only technique that can provide high resolution wave velocity profiles for deep profiles (deeper than 200 m) The setup of a suspension logger is shown in Figure 3 A string of source and receivers is lowered into a fluid-filled borehole The ray path is source-fluid-surrounding material-fluid-receiver Figure 4 shows the time histories for S-wave profiling in southem Taiwan where the thickness of soil deposit is greater than 100 m The near and far receivers are the lower (R1) and upper (R2) receivers in Figure 3 The Pshyand S-wave velocities of the surrounding materials are inverted following the standard travel timeprocess between the two receivers and the results represents the average wave velocity between the two receivers (1 m apart) The inverted wave velocity profiles are plotted in Figure 5 and the top 15 m S-wave profile agree well with surface wave measurements in this area The velocity profiles of soil deposits will be beneficial to characterize seismic site response The main limitations in borehole logging are the effect of casing and coupling between the casing and surrounding material s on the measured response and the disturbance of surrounding materials during boring process which will be more significant in shallow and soft soils as shown in Figures 4 and 5
67
~
illuacutet lo~jork ~ CCiexcl-r
Arrruacutered 7-CondlJotor cable
~ OYDPS-170 ~ LoggeriReccfder
Cable Head lJ
Diskette lilfth DataHead RedlJcer
Ji k~ Uwer (R2) ReceIacuteIIE ~
Depth refe reiexcl-e locati on fur R1- R2 anatysis Ji 1
rrioj point of R eceIacutellers Q~m
Uoler (R 1) ----shy
ReceIacuteller
1D7 m 157 m
fl r-~ J oint Deplh reference localion 10r S- R 1 anatysis mid point of 314 m S- R 1 s padng10 m flexible
Is olaion Cylinder I I107 m 37 mJoint
Combined Sh and P-lAlaVe SOlJrce (S)
Soorce Drver 105m
Wlght 1~
lip
Overal Lenglh ~ 58 m
Nct to Scae
Figure 3 Setup of suspension P-S logger (from GEOVision)
68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
-15 1 = (~~
-201-1-~-
-25 t== ==~-~~~ ~ 8 -
f301 3~ -35
-40 1 ~
~~ -45 t=b=======3~ii~j~~lQf2= ~- -50 1 =~
-55~~ -60~
O 10 20 30 40 O 10 20 40
Time (ms) Time (ms)
Figure 4 Time histories for S-wave velocity profiling in southern Taiwan
Velocity msec 500 1000 1500 2000
00
101 Ii 1(
I E t~ Irc 30 1 iexcl 1 t
40 1 J 1 1 )
-e- S-Wave
501 1s I )
60 ( shy
Figure 5 P- and S-waves profiles from suspension logger
~lt
69
)jh Hnoicl Cc~middotmiddot
Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
~ ~ H~ iexcl~ltEJTjOtkr- _- iexcll (1
Irrput1 SnptlibJdlal(a) ~14r o D ViImlIan or Randoo1~
~2 ~1 bullJJ
I(~a 11
)IFI I
t-+ iexcl~ - (c)
t--- ~
11Jiacutetciexclf Iiacute IltlpIiM CUnlteJira 1amp bull
~ J
Ibofo-Hz ~HE ~J2
el f ~ 0 1(b) ntilde
6 _LI
(gt
2m laquoID BIXI IOI) 1_ H
I-=iexclu Hz
Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
i~btNJWt D_ -- _
O-1m
n-2m
0-
o bull
~ Expentildemenlal []iexclpasiln CuIV4t
Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
~ shy-~ 11~
iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
1-D Svaloclty (Vs) PrcfU6
S-Vli1hxlty~)~riexclII~)
29) ~(J iexclro 1CCjI)= j F
1 ltshy
21__ ~_----+-_J~_ shy 811 middott 1la
J =shyo a
~f -- -j _+- _ -+- iexclf
lO
MultfChannel Record
otr1tt (ni)
20 laquoJ ~I) so 1CUacute Q ~imltrt1~~~
~
S
g fij~~7 LI Ii olI_
lrllltv~m~sect bull tI tl~ fh
ergt(nriexcl~)
D~~ lmag(t --1-i1 ~ ~tI1J1)
II~ E B
A
73
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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68
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
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Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
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Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
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70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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A
73
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
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Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
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La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANALYSIS
near far
-15 1 = (~~
-201-1-~-
-25 t== ==~-~~~ ~ 8 -
f301 3~ -35
-40 1 ~
~~ -45 t=b=======3~ii~j~~lQf2= ~- -50 1 =~
-55~~ -60~
O 10 20 30 40 O 10 20 40
Time (ms) Time (ms)
Figure 4 Time histories for S-wave velocity profiling in southern Taiwan
Velocity msec 500 1000 1500 2000
00
101 Ii 1(
I E t~ Irc 30 1 iexcl 1 t
40 1 J 1 1 )
-e- S-Wave
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Figure 5 P- and S-waves profiles from suspension logger
~lt
69
)jh Hnoicl Cc~middotmiddot
Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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)IFI I
t-+ iexcl~ - (c)
t--- ~
11Jiacutetciexclf Iiacute IltlpIiM CUnlteJira 1amp bull
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Ibofo-Hz ~HE ~J2
el f ~ 0 1(b) ntilde
6 _LI
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Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
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Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
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iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
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lO
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otr1tt (ni)
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~
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g fij~~7 LI Ii olI_
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ergt(nriexcl~)
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73
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o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
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V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
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74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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01 02 03 04 O 00002 00004 00006 00008 0001
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(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
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Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
)jh Hnoicl Cc~middotmiddot
Nonintrusive seismic methods N onintrusive seismic methods measure the wave propagation parameters on ground surface without invading the ground by drilling Depending on source types nonintrusive methods can be classified as active and passive methods The nonintrusive active methods include reflection survey refraction survey and surface wave methods There are many passive methods that use the background noise as the source have been developed or under development In reflecting the scope of the paper microtremor measurement analyzed with N akamura technique (1989) for identifying the site amplifications characteristics is presented
Refleetion survey
Reflection survey is one of the most common seismic methods The basic principal of reflection survey and offset-time curve for a single layer is shown in Figure 6 The reflection method generally uses the first arrival of P-wave to construct the offset-time curve to determine the thickness and P-wave velocity of soillayers However interferences between reflected refrac~d and surface waves increase the complexity of seismic data Consequently various testing layouts and signal processing techniques have been developed to enhance the signals of specific travel paths The complexity of wave field has limited the applicability of the reflection survey in near-surface survey
s
H
Pvtgt VSI ~T
]Lv bull P2 Vpz VS~
Figure 6 Principal of reftection survey and offset-time curve (Richart et al 1970)
Refraetion survey
Refraction survey uses the critically refracted wave from a higher velocity layer that underlies lower velocity sediment Seismic refraction testing is an established geophysical method for identifying subsurface soil stiffness and layer interface at shallow depths The principal of refracted method and offset-curve are shown in Figure 7 Limited by requirements of critical refraction at boundaries the refraction method is only applicable for stiffness increasing profiles
s 1 x bull I
x-2H tonie
p VP1
X VpzgtVP1 P2vn
Figure 7 Principal of refraction survey and offset-time curve (Richart et al 1970)
70
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
~ ~ H~ iexcl~ltEJTjOtkr- _- iexcll (1
Irrput1 SnptlibJdlal(a) ~14r o D ViImlIan or Randoo1~
~2 ~1 bullJJ
I(~a 11
)IFI I
t-+ iexcl~ - (c)
t--- ~
11Jiacutetciexclf Iiacute IltlpIiM CUnlteJira 1amp bull
~ J
Ibofo-Hz ~HE ~J2
el f ~ 0 1(b) ntilde
6 _LI
(gt
2m laquoID BIXI IOI) 1_ H
I-=iexclu Hz
Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
i~btNJWt D_ -- _
O-1m
n-2m
0-
o bull
~ Expentildemenlal []iexclpasiln CuIV4t
Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
~ shy-~ 11~
iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
1-D Svaloclty (Vs) PrcfU6
S-Vli1hxlty~)~riexclII~)
29) ~(J iexclro 1CCjI)= j F
1 ltshy
21__ ~_----+-_J~_ shy 811 middott 1la
J =shyo a
~f -- -j _+- _ -+- iexclf
lO
MultfChannel Record
otr1tt (ni)
20 laquoJ ~I) so 1CUacute Q ~imltrt1~~~
~
S
g fij~~7 LI Ii olI_
lrllltv~m~sect bull tI tl~ fh
ergt(nriexcl~)
D~~ lmag(t --1-i1 ~ ~tI1J1)
II~ E B
A
73
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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103
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATlON ORIENTEO ro SEISMIC ANALYSIS
Surface wave methods Surface wave methods are the most vigorously growing seismic methods in shallow depth profiling for the past decays The nonintrusive fast and large sampling area make thern very attractive for near-surface (less than 30 m) geotechnical site characterization as screening tools and are the only choice for hard samplel drilling soils The basis of surface wave methods is the dispersive characteristics of Rayleigh waves in layered system The phase velocity of Rayleigh wave V R depends primarily on the soil stiffness over a depth approximately one wavelength As a result Rayleigh waves with different wavelengths will sample different depths and the phase velocity will vary accordingly Although several surface wave methods have been employed in near-surface characterization the spectral analysis of surface waves (SASW) method (Stokoe and Nazarian 1985) and the multi-channel analysis of surface wave (MASW) method (Park et al 1999) are the two most popular methods In spite of differences in testing arrangements and data processing procedures for different methods surface wave methods all contain three stages which are data acquisition construction of field dispersion curve and inversion process for establishing representative shear wave ve10city profile r
The process ofSASW method is summarized in Figure 8 and details ofthe method can be found in Stokoe et al (2004) The SASW method is a simple technique required only two receivers at multiple source-receiver configurations to construct the field dispersion curve via spectral analysis After the construction of field dispersion curve iterative inversion analysis based on apparent velocities and the dynamic stiffness matrix method (Kausel and Roesset 1981) is performed to find the representative shear wave velocity profile that best matches the field dispersion curve
The MASW method uses the same data acquisition configuration as the reflection survey which involved multichannel recording Then the time-space data are transformed into frequency-phase velocity dorna in to identify the trends of dispersion from the pattern of energy accurnulation termed as phase-shift rnethod (Park et al 1998) This process is capable of capturing the multi-modal dispersion features Because the constructed field dispersion curves could contain multi-modal dispersion features a multi-modal inversion is adopted to infer the soillayering The process for ID testing is shown in Figure 9 Cornparison between MASW with multi-modal inversion process and Seismic CPT (SCPT) for a liquefaction study site at Southern Taiwan is plotted in Figure 10 and the results show a very good agreement between the two techniques
HVSR technique The horizontal to vertical spectral ratio (HVSR) technique proposed by Nakarnura (1989) is one of the effective ways of characterizing the predominant period (To) of a soil deposit or soft layer aboye bedrock The Nakamura technique allows one to evaluate the predominant frequency ofthe soft layer by measuring the tremor on the surface at a single station Because predominant period is a direct index for seismic amplifications spatial variations ofpredominant period will be useful in seismic microzonation In addition the average shear wave velocity of the entire soil deposit can be inferred from the quarter wave law
H (4)To = 4V
s
where H is the soil thickness The concept of Nakamura technique is illustrated in Figure 11 The logic behind the HVSR technique is that the vertical motion is less sensitive to amplification than the horizontal motion and can be seen as the bedrock motion Therefore the quasi transfer spectrum (QTS) can be defined as the ratio of the horizontal over vertical motion spectra and the peak of QTS represents the predorninant period ofthe soft layer Figure 12 shows a HVSR rneasurement performed on a reclaimed harbor in Taiwan The spatial variation of predominant frequency agrees with the distribution of filled materials in which the gravel backfill zones shows higher predorninant frequency
71
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Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
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72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
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Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
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o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
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Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
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and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
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Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
~ ~ H~ iexcl~ltEJTjOtkr- _- iexcll (1
Irrput1 SnptlibJdlal(a) ~14r o D ViImlIan or Randoo1~
~2 ~1 bullJJ
I(~a 11
)IFI I
t-+ iexcl~ - (c)
t--- ~
11Jiacutetciexclf Iiacute IltlpIiM CUnlteJira 1amp bull
~ J
Ibofo-Hz ~HE ~J2
el f ~ 0 1(b) ntilde
6 _LI
(gt
2m laquoID BIXI IOI) 1_ H
I-=iexclu Hz
Fipre 7 Spectral-illllll)$ilHH-surfacc-wavC$ (SASW) method Cakutation ofpb1ISC veocmcs
i~btNJWt D_ -- _
O-1m
n-2m
0-
o bull
~ Expentildemenlal []iexclpasiln CuIV4t
Figure 8 Process of spectral-analysis-of-surface-waves method (Stokoe et al 2004)
i~
~ shy-~ 11~
iJ~ i~
72
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
Scimlic
A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
1-D Svaloclty (Vs) PrcfU6
S-Vli1hxlty~)~riexclII~)
29) ~(J iexclro 1CCjI)= j F
1 ltshy
21__ ~_----+-_J~_ shy 811 middott 1la
J =shyo a
~f -- -j _+- _ -+- iexclf
lO
MultfChannel Record
otr1tt (ni)
20 laquoJ ~I) so 1CUacute Q ~imltrt1~~~
~
S
g fij~~7 LI Ii olI_
lrllltv~m~sect bull tI tl~ fh
ergt(nriexcl~)
D~~ lmag(t --1-i1 ~ ~tI1J1)
II~ E B
A
73
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
Fr~hJ r[t-tz)~IL__~~~~~~
Figure 9 Process of MASW method (KGS 2010)
~shy I 1
GI --
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A AIra4 D Retkdion B Dl$tl Wave E R~JhiexclctloJIIi tOacuteO SUtr1C~ W~ ~iIIMIldt) r Jrd 8~tiexclsfltBqtSur(aev1-e el Swru~ ~Ye (1Iightl Modes) G AiacuterIbiw CUlbiIIti N)jEgto
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lO
MultfChannel Record
otr1tt (ni)
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~
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ergt(nriexcl~)
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A
73
80 120 160 200
o---1-r-----L----L-j
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5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
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Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
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ebullbull~ 04~ en~
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~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
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oo~ o 004
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Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
80 120 160 200
o---1-r-----L----L-j
Silty clay (CL)
5 -Silly sand (SM)
sect 10t - Silty clay (eL)
- Q
o o o
-MASW - Silty ciay (CL) 15 -l D SCPT
o
J o
I I II I I 1
80 120 160 200
V (mis)
Figure 10 Comparison ofVs profiles from SCPT and multi-modal MASW
lIeIIlOC surface waves
Fig L Typical geological struaure of a sedimentarybasin
f tmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotlmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotImiddot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot ~
i ~
t
3[0
Figure 11 Concept ofNakamura HVSR technique (Carniel et al 2008)
o fo 10 f(Hz]
74
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Campanella R G and Robertson P K (1988) Current status of piezocone test Proc Intemational Symposium on Penetration Testing ISOPT-1 Orlando Vol 1 pp 93-116 Balkema Pub Rotterdam
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
Carter 1 P Booker 1 R and Yeung S K (1986) Cavity expansion in cohesive frictional soils Geotechnique Vol 36 No 3 pp 349 - 358
Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
Huang A B and Hsu H H (2004) Advanced calibration chambers for cone penetration testing in cohesionless soils Proc ISC-2 on Geotechnical and Geophysical Site Characterization Porto Portugal VoLl pp147-167
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
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Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
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-
103
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO ro SEISMIC ANALYSIS
27
15 L~
1 bull
1111 ~ 11 1 ns
Figure 12 Spatial variation of predominant frequency in a reciaimed harbor
DEFORMATION AND DAMPING CHARACTERISTICS
For seismic analysis the deformationand damping characteristics generally involve the relationship between modulusdamping ratio and strain The importance oflocal strain measurements in the determination of soil deformation characteristics in laboratory tests has long been recognized (Burland 1989) Severallaboratory deformation measurement techniques with sub-micron resolutions have been developed in the past few decades (Scholey et al 1995) By lJlounting the measurement devices directly on the soil specimen deformation as well as damping characteristics under a wide strain range can be measured using a single specimen (Toki et al 1995) Figure 13 shows the stress excess pore pressure and strain relationships from a monotonic triaxial test on a clean Mai Liao Sand specimen Local axial strain was measured using a nonshycontact proximitor Figure 13(b) depicts the part of stress-strain relationship where axial strains are less than 10-3 The result is consistent with the general understanding that sand should have an elastic or linear elastic behavior under a threshold strain of approximately 10-2 (Dobry et al 1982 and Jardine 1992)
Bender elements reported by Dyvik and Madshus (1985) provide a quick and economical determination of maximum shear modulus (Gmax or Go) on soil specimens via shear wave velocity measurement The shear strain caused by bender element vibration is believed to be les s than 10-3 (Dyvik and Madshus 1985) The deformation and damping characteristics that covers the full range of strains involved in a typical seismic analysis can be realized using cyclic triaxial tests with local strain and bender element measurements Figure 14 shows the results from cyclic triaxial test with G using bender element measurements on a single silty
o
sand specimen from Southern Taiwan The local strains were measured using a pair of local displacement transducer (Goto et al 1991) The equivalent shear modulus (Geq) and damping ratio (h) were determined based on a series ofunload-reload loops with different shear strain (y) amplitudes
75
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
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Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
~ ~
ln jei nOiiorll C011er(o- Gc rr ji1-el_~ ~
60rl----------------------~
50 os
~40 en en 06 r---------------- (1)
~30 ebullbull o ~ ~20 os emiddotmiddotp
ebullbull~ 04~ en~
0 10 (1) b
O ~ ebull shy
O ~ 16
os ~ 02 f- ~ 12 q
~ 8 4
~ O
01 02 03 04 O 00002 00004 00006 00008 0001
Axial strain Axial strain
(a) Stress excess pore water pressure (b) Stress-strain relationship in srnall strain
and strain relationship
Figure 13 Monotonic triaxial compression test on a Mai Liao Sand specimen
35 028 --os C) y - Geq
~ 30 lt) y-h 024 -- ~
~ cr
SrO 25 02 G os en~ ol O) g 20 016[ o 0lt0 (l ElEl os 15 012 ~ Q)
P en ltO 11 ~ ltgtltgt
11 10 deg 0 008 ~ 11 gt-oro rgt- ltgt o-6- 5
oo~ o 004
~
O 00001 0001 001 01
Shear strain y ()
Figure 14 Cyclic triaxial test with G measurements on a single silty sand specimen o
Sorne ofthe in situ testing rnethods can also fulfill the function or at least part ofdeformation characteristics measurernents in the field Figure 15 shows a coHection of such in situ testing methods and the range of strains that can be used to infer deformation characteristics The seismic geophysical tests can be used to determined G o The pressurerneter test (PMT) rneasures the relationship between its probe expansion pressure and radial strain and hence is ideal for rneasuring the shear modulus - shear strain or G-y relationship Using highly sensitive strain sensing arms and unload-reload loops in PMT the G-y relationship that refiect
76
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTE OTO SEISMIC ANALYSIS
relative1y undisturbed soil conditions can be obtained (Fahey 1998 and Wang and ORourke 2007) Figure 16 shows the results of a PMT with unload-reload loops The test was conducted in a soft rock at the campus ofNational Chiao Tung University in Hsin Chu Taiwan The PMT strain arms and expansion pressure were monitored with fiber optic sensors With this system the secant shear modulus degradation that corresponds to a minimum shear strain of 10-3 was obtained
Reglanor -- Range far --1_Bearing Capacity _1
tGNsical l Deformation I and Stability Testaacute- Analyses Catculations
CJ -(1) J Unload-Reload PMT
Flat DMTJ O 8crO ~ ampo~ l1 ~1 l as (1) Initial Loading p ~ Penetration
s --_ Testaen -------shy108 10-5 10-4 10-3 10-2 10-1
Shear Strain Y8 Figure 15 Conceptual variation of shear modulus with strain level under static monotonic
and relevance to in situ tests (from Mayne et al 2002)
600-------------------~~-----5rl----------------------------~
4 rshy
iJ t )
400
ro
~
+
bull +
bull bullbull 6 bullbull +
~ 200 shy ~~
1 ~- I
ll lO 1O~ 0 1
O 5 10 15 20 25 00001 1 001 01 000 Shear strain ~ Strain
Ca) PMT expanslOn (b) Modu us 1 degradabon
Figure 16 PMT with unload-reload loops in a soft rock
The seismic fiat dilatometer test CSDMT) provides two data points (1) the initial modulus Go from shear wave velocity measurement (Equation 1) and (2) a working strain modulus corresponding to the DMT constrained modulus MDMT The G-y curve can be constructed by fitting reference typical-shape curve through the two data points from SDMT (Marchetti et al 2008) Similar two point approach can also be applied using the seismic cone penetration test (SCPT) In this case the Go from Vs and a modulus va1ue that corresponds to strain induced by cone penetration is inferred from the cone tip resistance
77
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
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La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
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Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
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Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
I jiexcl~on_iexcl I
UNDRAINED CYCLIC STRENGTH FROM IN SITU INDEX TESTS
A major concem to geotechnical engineers from a soil behavioral point of view is the potential of cyc1ic liquefaction for a given seismic event (eg a design earthquake) There are general1y two avaiIabIe approaches to assess the potential of cyc1ic liquefaction of a given soil deposit (1) use of Iaboratory testing on undisturbed samples and (2) use of semi-empirical relationships that involve correlations of observed field soil behavior with in situ index tests Taking undisturbed samples in sand and conducting laboratory testing can be complicated and prohibitive1y expensive Thus the laboratory testing approach is usually reserved for research applications and rarely used in geotechnical engineering practice
The semi-empirical field-based methods (Idriss and Boulanger 2006) which evolved from the simplified procedure by Seed and Idriss (1971) are by far the most widely used methods in assessing the cyc1ic liquefaction potential of sand The simplified procedure has two essential compojlents (1) an analytical framework to organize past case history experiences and (2) a suitable in situ index to represent soil liquefaction characteristics (Idriss and Boulanger 2006) In situ penetration tests have proved to be usefuI for representing soil liquefaction characteristics because they not only provide an indication of denseness but also reflect other important characteristics such as fabric gradation cementation age and stress history (Seed 1979)
The simplified procedure provides a boundary curve that separates cases of observed liquefaction and those with no notable liquefaction in a two-dimensional plot of seismic loading in terros of Cyc1ic Stress Ratio (CSR) versus a norroalized in situ index test value The boundary curve also serves as a correlation between the in situ index test value and the Cyclic Resistance Ratio (CRR) The terro CRR may be considered as the maximum CSR that a soil can resist before liquefying Traditionally the result ofthe liquefaction potential analysis using the simplified procedure is presented in terms of a factor of safety (Fs) defined as the ratio ofCRR over CSR No soilliquefaction is predicted ifFs gt 1 The assessment ofliquefaction potential in terros of factor of safety is general1y known as the deterministic approach In recent years there has been an increased effort to quantify the generally unknown degree of conservativeness that existed in the published boundary curves and to assess the liquefaction potential in terros of probability of liquefaction (eg Cetin et al 2004 and Juang et al 2002 2006) Details ofthe probabilistic approach are beyond the scope ofthis papero
Four in situ index test methods have be en identified by Youd et al (2001) as having reached a level of sufficient maturity for the purpose ofsoilliquefaction potential assessment under the framework ofsimplified procedure These tests inelude (1) standard penetration test (SPT) (2) cone penetration test (CPT) (3) shear wave velocity (Vs) and (4) Becker penetration test (BPT) BPT is used primarily for tests in gravely deposits and readers interested in BPT are referred to Harder and Seed (1986)
Liquefaction Potential Assessme~t for Clean Sands The oldest and probably the most widely used in situ index test method is the SPT A relationship between CRR and the SPT N value (blow count of hammer required to penetrate a split barrel sampler for 1 ft or 300 mm) corrected to a hammer energy ratio of 60 and norroalized to an effective overburden stress (Jvo) of 100 kPa (or 1 atm) [designated (Niexcl)6o] is used to represent the boundary curve Figure 17 presents the CRRshy(Niexcl)60 correlations published in the past 3 decades for c1ean sands (fines content FClt5) and earthquake events ofmagnitude M = 75 Fines are defined as partic1es passing 200 sieve (material lt 0075 mm) The modifications in CRR-(Niexcl)60 correlations over the years general1y recognized a more significant increase of CRR as (N iexcl)60 reached values about 30
78
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Campanella R G and Robertson P K (1988) Current status of piezocone test Proc Intemational Symposium on Penetration Testing ISOPT-1 Orlando Vol 1 pp 93-116 Balkema Pub Rotterdam
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
Carter 1 P Booker 1 R and Yeung S K (1986) Cavity expansion in cohesive frictional soils Geotechnique Vol 36 No 3 pp 349 - 358
Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
Huang A B and Hsu H H (2004) Advanced calibration chambers for cone penetration testing in cohesionless soils Proc ISC-2 on Geotechnical and Geophysical Site Characterization Porto Portugal VoLl pp147-167
Huang A B Huang Y T and Ho F J (2005) Assessment of liquefaction potential for a silty sand in Central Western Taiwan Proc XVI ICSMGE Osaka pp 2653 - 2657
Huang A B and Huang Y T (2007) Undisturbed sampling and laboratory shearing tests on a sand with various fines contents Soils and Foundations Vol47 No 4 pp 771 - 781
Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
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potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
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Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
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Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
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Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
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Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
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102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
The SPT is a versatile testing method applicable to soils with a wide variety of gradation and density conditions The equipment and skilled technicians required to perform the SPT are readily available in most parts of the world and thus there exists a large database A soil sample albeit disturbed can be retrieved with the split barrel sampler along with the SPT The gradation and other important basic physical soil properties can be measured directly in the laboratory These are important advantages in favor of the use of SPT for soilliquefaction potential assessment The equipment such as the rope dimensions ofthe cathead type of harnmer and details in the split barrel sampler (Seed et al 1984) can all affect the measured SPT N values It is imperative to follow the relevant standards when using the SPT (ASTM D1586-08a and associated energy measurements in D4633-05)
06 CDSeed 1979 reg IZgtSeed and Idriss 1982
05 _ ~sSeedd et all 21090841NCEER Workshop ~~~L __j oJSlL ~ ee et a 11 regIdriss and Boulanger 2006 dJ (j) J
04 ----+- -bull--+-~ middotfmiddot~middot~middot~middotmiddota t6- Q _ a ~ O 5 03 -- - -~~ -- -- -- --~~~o--- a o (j) 0- _ )0 o O ~4i _ oiexcl--- o o o o
02 -- -- bullbull -~e~- iexcl--middotmiddot-~middot~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-------middot-middot----------middotOacute-----I
ro- 01 ~~middot--middot---o)---middot--middot------ - uumlquefactiono (bO o
o o bull Marginal Liquefaction
o No Liq-efaction o
o 10 20 30 40 (N1)6o
Figure 17 CRR-(N1)60 correlations published in the past 3 decades for clean sands (after Idriss and Boulanger 2006)
The CPT can be highly automated and yields an almost continuous stratigraphy of the soil deposit The quality of test data can be substantially enhanced with the addition of piezo unit(s) and seismometer(s) (ie the seismic piezo-cone penetration test SCPTU) The additional information can be helpful for soil liquefaction potential assessment Unlike SPT no soil sample is retrieved in regular CPT A soil c1assification is required as a priori in the use of CPT for liquefaction potential analysis Robertson and Wride (1998) proposed a soil behavior index le for the purpose of soil classification where
2 2]05le =[(347 -logQt) + (logFr +122) (5)
Qt = (qt - avo ) ~o (6)
Fr = [fsl(qt -Ovo)]100 (7)
in which qt = cone tip resistance corrected for pore pressure effects (Campanella and Robertson 1988) f = CPT sleeve friction cr = in situ total vertical stress and a = in situ effective vertical stress 1 is a soil s vo vo e
behavior type index that ranged from approximately 13 to 36 Lower value corresponds to clean sand and
79
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Campanella R G and Robertson P K (1988) Current status of piezocone test Proc Intemational Symposium on Penetration Testing ISOPT-1 Orlando Vol 1 pp 93-116 Balkema Pub Rotterdam
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
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Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
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Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
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Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
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Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
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Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
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La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
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Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
1 ~1 in1e~ middotTOnCUacute CC~-
the soil tends to have claylike behavior when 1 gt 26 Robertson (2009 and 2010) emphasized that 1 is a e e
Soil Behavior Type (SBT) c1assification indexo The le based SBT classification may not be consistent with that from the Unified Soil Classification System (USCS)
For a given density state qt increases with stress in a non-linear fashion The rate of qt increase reduces as the stress becomes larger and the dilatancy effect diminishes A single stress normalized cone tip resistance value is generally used to reflect the soil density state in the evaluation ofsoilliquefaction The dimensionless normalized cone parameter Qtn is defined using the following format (Robertson 2010)
Qtn = [(qiexcl -Ovo)jPa](Padvor (8)
j where Pa is the atmospheric pressure and n is the stress normalization exponent that varies with SBT Soil dilatancy is related to stress grain characteristics and mineral content as well as density Recent studies (Idriss and Boulanger 2006 Moss et al 2006 Cetin and Isik 2007 and Robertson 2009) have gene rally agreed that for c1ean sand n = 05 and in clays n = 10 Robertson (2009) refined the correlation between n and soil behavior type as
n = 0381(IJ +005( dyol Pa) - 015 (9)
where n ~ 10 Figure 18 shows a selection of correlations between CRR and Qtn published within the last decade for clean sands and earthquake events of magnitude M = 75 There are different levels in conservatism among these published CRR- Q correlations as Q exceeds 100
- tn tn
09 o Non-liquefied JlJang et al 2006 bull Moss 2003
08 Liquefied_ 0-bull Ij
Q bull iexcl Icio07 t o j
Robertson and I
06 Wride1998 cr
ti oacutel iacute
cr O 05 bull bullbull -- iexcl- bull --f Lo 1ijJiexcl o (o iexcliexclQ 1
iexcliexcl ~ffi 04 bull ~ rot - o 0 02 gt ~ tI oO
bull 0-003 -- --ji --~ 6 -- --
iexcl l ~o 7 -(_ 0
qP~ CJO o02 -lt[oacute--~middotmiddotmiddotmiddotmiddoto 0000 o
-gtG------ 00 o o01 o 8 Idriss and Boulanger 2006
O O 50 100 150 200
Qtn
Figure 18 A selection of CRR-qclN correlations published recently (after Juang et al 2006)
80
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
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Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL AND GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
Forthe fiat dilatometer test (DMT) developed by Marchetti (1980) the horizontal stress index (Ko) has been demonstrated to have clear correlations with Dr (Reyna amp Chameau 1991) at rest lateral earth pressure coefficient (K) (Monaco et al 2005) and most importantly the age of sands (Marcehetti et al 2008 and Marchetti 2010) These characteristics make DMT favourable as a viable in situ index test method for the assessment of soil liquefaction potential Figure 19 surnmarizes the various CRR-Ko (for earthquake magnitude M = 75) for clean sands reported by Marchetti et al (2008) The fiat dilatometer is rugged and more capable in penetrating through dense granular materials than the cone penetrometer The DMT control console and its test procedure are simple and results are not operator dependent A drawback with the use of DMT is the lack of a large database As in the case of CPT no soil sample is obtained in DMT The soil gradation needed for liquefaction potential assessment is estimated from empirical rules
05
LlQUEFACTION
04
cr cr 03 O shyo
o2 02
Robertson and Campanella 1986
01
NO LlQUEFACTlON o
o 2 4 6
Ko
Figure 19 Available CRR-~ correlations (after Marchetti et al 2008)
Nonintrusive Vs measurements like surface wave methods can be especially useful for sites underlain with gravelly materials where penetration tests such as SPT or CPT are not feasible The Vs can also be easi1y measured in a triaxial cell using bender elements By comparing the Vs from bender element test to the CRR obtained using the same soil specimen through cyclic triaxial tests it is possible to verify or establish the CRR-VS1 correlations using reconstituted (Huang et al 2005) or undisturbed samples (Baxter et al 2008) Figure 20 shows the CRR-VS1 (Vs normalized to a effective vertical stress of 100 kPa) correlations published by Andrus and Stokoe (2000) An important disadvantage in the use ofVs is a lack of sensitivity to the relative density Dr For a change ofDrof clean sand from 30 to 80 the corresponding SPT N value would increase by a factor of71 and q by a factor on3 The same D would be expected to change the V
t r s by a factor of 14 based on available correlations (Idriss and Boulanger 2006)
Roy (2008) compiled a databas e from 24 test sites in different parts ofthe world to analyze the correlations among CRR qt and V The data included laboratory tests on high-quality (undisturbed) soil samples field CPT soundings and Vs measurements from near sampling locations The sands had a wide range of fines contents age and soil grain compressibiliiy The analysis did not indicate a coherent correlation between Qtn or VS1 and CRR Instead Roy (2008) reported that the ratio of qt to maximum shear modulus (G) relates
8 10
81
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
reasonably with CRR using separate correlations that depend on geologic age Two boundary curves that separate the liquefaction region from no-liquefaction cases in the CRR-qGo space can be identified as shown in Figure 21 one for Holocene and one for Pleistocene soils The maximum shear modulus (G ) is
o determined from V measurements The CRR-qG correlations are independent of the fines content and
s t o
soil grain compressibility The use of CRR-qG correlations avoids the complexity of adjustment andort o
normalizations ofthe individual index parameters to account for fines contents and stress conditions When using the seismic cone penetration tests V measurements can be easily coupled with CPT directly to obtain
s
q G values t o
06
t~drus and Stokde 2000) 4 ~ _____ ~ - ~ ~ ~t350 S5 h_ _____ ~____ _ ~ _ __ ~ ~______ ~ ~ ___ ~ F-_ _ ____ ~ Fe ~ ~ ____ ~ ~__ ___ ~05
I j
04 1
o o u o 03 o Cf)
u S Olneyvillle Silt 02 A Fanners Market Silt
bull Niigata Sand 01 ~ Toyoura Sand
Q Mai Liao Sand
o 100 150 200 250
Figure 20 The CRR-V1 correlation proposed by Andrus and Stokoe (2000) and other sandssilts (after Baxter et al 2008)
--Holocene - - - Pleistocene
Q HoloceneLiquefaction o HoloceneNo liquefaction 08 bull PleistoceneLiquefaction o PleistoceneNo liquefaction o I
~ 06 bull lmiddot u o o o bull o ~( bull bull (f) bull o - ~ f o U 004 bull bull ( []J bull
bullbull bullbullbull o o ~ljt (sectld b o bull la
~ ~~ o
o 02
~o~J~~~ ~ o --~ ~ b
o 0
o o 01 02 03 004
qiexcllGo
Figure 21 The CRR-qGo correlations reported by Roy (2008)
82
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
Ishihara and Harada (2008) analyzed the correlations between SPT and CPT results and their relationship with the ratio of effective horizontal stress to vertical stress (K) The CRR values were estimated from D
r
The penetration resistance values from SPT and CPT were based on calibration chamber tests Figure 22 shows the comparison ofthe CRR-qiexcl correlations derived for three clean sands Toyoura sand (average grain size Dso = 020mm) Da Nang sand (Dso = l13mm) and Monterey sand (Dso = 037mm) for K=05 The correlations by Robertson amp Wride (1998) and AIJ (2001) are also included for reference For these three types of clean sands the CRR-qiexcl correlations can deviate significantIy from the published curves and among themselves Similarly discrepancies can also be found among the CRR-N correlations derived for Toyoura sand and those reported by Youd et al (2001) and JRA (1996)
08 ------- AIJ
_- Robeltson amp Wride 1998
06 --Toyoura sand
---=UaNarigsarid - JII
--Mont$ry sand
ri 04 uuml
02
o o 5 10 15 20 25
qt MPa
Figure 22 Comparison of the CRR-qt correlations derived for three clean sands (after Ishihara and Harada 2008)
Liquefaction Potential Assessment for Sands with Fines Natural sand deposits ofien contain various amounts offines (silt and clay size particles) It has been reported that most cases of earthquake-induced liquefaction have actually occurred in silty sands (Yamamuro and Covert 2001) Researchers have generally agreed that as fines contents exceed 5 relative density ceased to be a reliable index to predict liquefaction potential (Seed et al 1985 and Ishihara 1993) For fine grained soils the cyclic resistance correlates well with the void ratio where a lower void ratio corresponds to greater cyclic resistance (Ishihara 1996) There is stiU a lack of consensus as to what role the fines content plays in relation to liquefaction
When the CRR of a sand with fines is determined through in situ index test using simplified procedure the situation is more complicated as theavailable correlations are empirically derived mainly from field observations of soil behavior following earthquakes Although different in magnitude andlor format most available CRRs based on in situ index test value correlations for cohesionless silty sands suggest that a given index test value should correspond to a higher CRR as fines content increases Alternatively the in situ index test value should be increased to obtain an equivalent clean sand value For the Vs method by Andrus and Stokoe (2000) the adjustment in the CRR-VS1 correlations is included in Figure 20 The SPT penetration resistance (Idriss and Boulanger 2006) is increased to an equivalent clean sand value (N1)60CS
according to FC (in percent) as
83
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
~
1 5ih (nlmno1CrlOi Ccriexcli
1 l
(N) = (N) + ~ (N ) (lO) J
I 60es I 60 1 60
97 157 (11 )(NI)60 ~ exp(163 + FC + 01 - (FC + 01)2)
Robertson and Wride (1998) suggested that for CPT the equivalent c1ean sand value should be deterrninedl based on le using the following relationship
Qtncs = KcQtn (12)
For le S 164 Kc = 10 (13)
For le gt 164
Ke = -0403 + 558 - 2163 + 3375c -17 88 (14)
The adjustment to account for the fines content can impact significantly the outcome ofliquefaction potential assessment DespUumle this significance little explanation has been offered to justify the consideration offines content effects (lshihara 1993 and Ydud et al 2001)
Figure 23 shows a series of qt profiles in dry and saturated specimens from laboratory calibration tests in MLS reported by Huang et al (2004) For FC of 15 the qt profiles in dry and saturated specimens are essentially identical upon reaching a stabilized value indicating that the cone penetration is drained When FC exceeds 30 the qt in saturated specimens is significantly lowered than that in dry specimens Similar partial drainage phenomena have also been reported by Campanella et al (1981) for CPI in c1ayey silt
qiexclMPa
O 5 10 15 20 O 1 2 3 4 5 O 1 2 3
O
~ 200
sect ~
__ _1 _____ 1 __ _~ 400 (D c shyo I
g 600
-----cWshyo
800
Figure 23 Measured qt profiles from CPT calibration tests in MLS at different fines contents (after Huang and Hsu 2004)
By comparing the CRR and qt from CPT calibration tests in reconstituted specimens with comparable fines contents density and stress states it was possible to verify the CRR-Qtn correlation by direct comparisons
84
-sat -dry
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
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Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
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Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
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Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
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Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
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Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
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Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
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Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
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Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
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102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAlYSIS
for MLS as shown in Figure 24 (Huang et al 2005) The CRR values were determined based on cyclic strength obtained from a series of cyclic triaxial tests The results as shown in Figure 24 indicate that the fines content adjustment becomes significant only when the fines start affecting the drainage conditions in CPT and thus result in a group of data points with distinctly lower Qtn A similar explanation has been postulated by Thevanayagam and Martin (2002) The laboratory study in MLS seems to suggest that a more effective Qtn adjustment scheme should be based on CPT drainage conditions rather than fines content
Additional CRR- Qtn data points based on field CPTU and cyclic triaxial tests on undisturbed samples are also included in Figure 24 The data compiled by Tokimatsu et al (1995) were collected from 6 test sites where soil samples were retrieved by freeze sampling The fines contents varied from lt1 to as much as 30 According to Tokimatsu et al (1995) there was a unique CRR-Qtn correlation irrespective of fines content For a given Qtn the dispersiveness in CRR was attributed to changes in K and soil type represented as a function of minimum void ratio
In 1ight of the aboye findings Huang et al (2005) suggested that a pore pressure dissipation test during CPTU may be used as a reference to scale the amounts of fines content adjustment For the CPTU in saturated specimens inc1uded in Figure 23 a dissipation test was conducted in the chamber (at respective depths of 125325 and 375mm for FC of 15 30 and 50) In a dissipation test the cone penetration was suspended and the dissipation of the excess pore pressure induced by cone penetration was monitored until its full dissipation When the FC exceeded 30 there was a distinct increase of qt at the start of the subsequent push The qt setup increased furtl1er as the FC reached 50 This phenomenon referred fo as the qt setup was also reported by McN eilan and Bugno (1984) in their experience of CPT in offshore Galifornia silts The reason for setups is that partial drainage caused a lowered qt due to pore pressure accumulation The dissipation of pore pressure increases soil strength against cone penetration and generates the setup There is no obvious qt setup for the case ofFC=15 in Figure 23 a result that is consistent with the fact that CPT is drained as mentioned aboye
06 (082) amp (089) iexcl F4
o +I----~---------~-------_T-----o _ 100 200 300 400
Qtn
(Robe~on amp Wride 1998) or (Stark amp Olson 1995)
FC=35 FC=15
04 t aa u es a (J)
u iexcl
02
elean sand
FC KMLS
bull o 05
bull 15 05
Aacute 30 05
o o 1
o 15
t 30
FC KYLS
bull 18 05
a 43 05
11 89 05
Tokimatsu el al FC K
liI lt1 05
bull lt1 1
bull 1-10 05
Aacute 1-10
El gt10 05
JI gt10 1
Figure 24 Laboratory and field calibrations of CRR-Qtn correlations
85
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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-
103
A series of CPTU using a standard cone (cone cross sectional area= 10 cm2) penetrating at 20mmsec (the standard CPTU rate) a Iarge cone (cone cross sectional area= 15cm2) penetrating at 20mmsec (the large CPTU) and a standard cone penetrating at 1mmsec (the slow CPTU) were conducted at the Yuan Lin test site The rate of consolidation for soil surrounding a cone tip is inversely proportional to the square of the cone diameter (Robertson et al 1992) Therefore changing the cone diameter can also duplicate the effects of penetration rateo The pore pressure element was located immediately behind the cone tip at the u2
position Profiles ofCTPU results that include friction ratio Rf (=~qt xl00) from tests at Yuan Lin site are shown in Figure 25 The results indicated no significant differences in qt among three types of CPTU considering drastic differences in cone size andor penetration rateo The slow CPTU was conducted at depth leve1s where Laval samples were taken The u2 values from large CPTU were most1y identical to those from the standard CPTU The u2 in slow CPTU matched well with the hydrostatic pressure uo indicating that 1mmlsec was slow enough to allow the penetration induced pare pressure to fully dissipate and reach equilibrium in most parts with the surrounding hydrostatic pressure
)J
q MPa u2 bull kPa R
o 5 10 15 250 o 250 500 750 o 4 8
o
5
10 E
(J)
o 15
t
Penetratian rateCan e area
cm2 mmsec
20 i--- 15 20 -10 20
-10
25
Figure 25 CPTU profiles from Yuan Lin site (after Huang 2009)
The standard CPTU was coupled with dissipation tests at a test site in Yuan Lin Taiwan The results in terms of qt profile are plotted in Figure 26 along with fines contents (from tests on SPT samples) The comparison between Figures 23 and 26 allows the change in qt and its relationship with pore pressure dissipation tests to be visualized The effects of partiacuteal drainage for CPTU in MLS were demonstrated by the presence of significant setups following a pore pressure dissipation test as shown in Figure 23 The field CPTU was close to drained conditions with essentially no signs of qt setup even when the fines contents reached as high as almost 100 The suspension of cone penetration in field pore pressure dissipation test caused a sharp decrease in qt and folloWed by a resumption of the original qt at the start of the subsequent push The drastic differences between CPTU in laboratory prepared well mixed silty sand and natural silt sand in the fieId are likeIy due to the heterogeneity existed in natural soil It is believed that the presence of c1osely-spaced free draining sand Iayers made the field CPTU behave as a drained test in a siIty soil mass At much wider range offines contents the lateral spread ofCRR-Qtn data points based on tests in Yuan Lin Soil (YLS) shown in Figure 24 was less than those from tests using the reconstituted MLS specimens or suggested by the avaiIabIe CRR-Q
tn correlations If differences in fines content are viewed as those of soil
types it can also be concluded that the fines content effects are Iess significant than soil types for the case ofYLS
86
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
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La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
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101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
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102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
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Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED 10 SEISMIC ANALYSIS
Using bender elements the Vs can be measured on the same soil specimen of cyclic shearing test The CRR-Vl correlation can thus be conveniently calibrated completely based on laboratory tests (Huang et al 2004 and Baxter et al 2008) Figure 20 shows CRR-VSI data points compiled by Baxter et al (2008) that include clean sands (Toyoura and Niigata sand) silty sand (Mai Liao sand with 0 ~ FC ~ 50) and non-plastic silt The silt specimens include those from undisturbed block samples split-barrel samples and reconstituted samples by a modified moist tamping method The result shows that the effects of soil type on CRR-Vsl correlation overshadow those offines content sample preparation methods and applications of pre-shearing or pre-stressing
q MPa Fe o 2 4 6 8 10 o 20 40 60 80 100
o ~ iexcl iexcl I -- ~
~
3 --- --q
~
6 ishyE
t iexcl Q)
o 9 ------~---+---_
1M bull iexcl iexcl
12 --9---------shy
~fi 15 ltT - --shy
Figure 26 Enlarged qt and fines content profiles from YLS site (after Huang 2009)
UNDISTURBED SAMPLING IN GRANULAR SOILS
Attempts oftaking high quality samples of cohesionless soi1s from be10w ground water tab1e can be traced back by at least half a century (Singh et al 1982) Challenges involved in taking good quality sand samples include prevention ofthe 10ss ofsample during withdrawal and damaging soil structure during transportation These challenges are formidable unless the samples are taken near the ground surface or by block sampling Yoshimi et al (1977) is believed to be the first among the more recent attempts in developing practical procedures ofground freezing and dry coring for sand sampling A column of sand is frozen in situ and then cored out ofthe ground surface Researchers from Japan and North America have generally considered in situ ground freezing (Hofmann et al 2000) and coring to be a superior method for obtaining undisturbed samples of sand
Driven by the demand in high-tech industry the cost of liquid nitro gen continues to decrease With a much lower temperature (-196degC) the efficiency and practicality of using liquid nitrogen for ground freezing can be much improved in contrast to the use of brine (-30degC) Provided that drainage is not impeded and that changes in void ratio are minimized during freezing the in situ structure can be reserved Studies have indicated that this structure preservation is possible if free drainage is allowed in at least one direction during freezing (Singh et al 1982) The reservation of soil structure is further enhanced if freezing is conducted under a confining stress (Yoshimi et al 1977)
87
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
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Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
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Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
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Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
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Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
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potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
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Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
_[iexcl-Ifnp
For silty sands especially when fines contents are high drainage can be significantly constrained in the field Ground freezing can cause void ratio changes due to frost heaving It is possible to retrieve samples in granular soiacutels by pushing a piston tube sampler under ambient temperature However the friction between the sampling tube and the sUITounding soil can be excessive when fines contents are 10w The sampling by pushing tends to loo sen dense sand and densify loose sand (Hofmann et al 2000) Good quality sampling is possible iffines contents are high (Bray and Sancio 2006) or samples are taken near the ground surface (H0eg et al 2000) with either a piston tube sampler or by block sampling (Baxter et al 2008)
Huang and Huang (2007) reported the use of Laval sampler to obtain high quality silty sand samples with fines contents ranging from 18 to 89 at Yuan Lin test site The Laval sampler as schematically described in Figure 27 was developed at Laval University (La Rochelle et al 1981) originally for taking high quality samples in sensitive c1ay The sampler was made of two main parts a sampling tube and an overcoring tube To take a sample the drill riacuteg pushed the sampling tube into the bottom ofthe borehole while rotating the overcoring tube N o freezing was applied in the ground The bottom of sampliIl tube was protruded at 20mm ahead of the steel teeth and cutters During penetration the head valve was kept open to allow drill mud circulation and thus removal of soil cuttings The Laval sample can be 450 to 550 mm long After a waiting period of 5 to 30 minutes the head valve was c10sed and the bottom of the sample sheared by rotating the inner rod The sample was then retrieved to the ground surface
BQ wire line drilling rod Collar Locking pin
Internal guide Internal guide
~I
~
_-=----=---c~ J
----- Overcoring tube
Steel (eth
I
r I gand~ SectionA-A
Carbon steel ZW pipe
Demensions in mm
i y$--7- Steel teeth and cutters
Figure 27 Schematic view of the modified Laval sampler (modified from La Rochelle et al 1981)
The Laval samples with FCgt30 were cut into 120 to 180mm long segments and sealed in the field without freezing The samples taken from soillayers with low fines contents (FClt30) remained in the sampling tube and kept vertical until it was completely frozen The soil along with the sampling tube was placed in a Styrofoam lined wooden box and gradually frozen from top of the sample by dry ice at -SOuacuteC A backpressure equal to the water head within the sample was appl1ed by means of nylon tubing connected
88
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTEO TO SEISMIC ANALYSIS
to the bottom of the sample to ensure that no water can drain under gravity The bottom drainage and backpressure assured that pore water drainage only due to water volume expansion during freezing (Konrad et al 1995) The frozen samples were stored in a freezer during shipping and laboratory storage until the time of shearing test
A specially designed coring device was used to cut 70rnm diameter triaxial specimens from the frozen Laval sample kept at -80degC by dry ice (Huang and Huang 2007) The specimen was then placed in the triaxia1 cell under a confining stress and thawed following the procedure suggested by Hofmann (1997) An important advantage of Lava1 sampler is its large size Four 70rnm diameter tri axial specimens can easily be cored from a single Laval sample at the same depth level The number of specimens is ideally suited for the determination of a CRR-N curve through cyclic triaxial tests As shown in Figure 28 the values of
e
Vs1 taken from the triaxial test specimens feH within the general range offield measurements near the Laval sampling locations indicating a reasonable quality ofthe soil samples Huang et al (2008) reported the use of a gel-push sampler to recover high quality samples in silty sands at a test site in Kao Hsiung of Southem Taiwan where the fines contents varied from 5 to over 60 The gel-push sampler developed in Japan (Tani and Kaneko 2006) was modified from a 75rnm Osterberg piston sampler (also known as a Japanese sampler) as schematically shown in Figure 29 The sand sample was obtained by pushing the gel-push sampler under ambient temperature as typically done for piston sampling in clays A water soluble polymeric lubricant (gel) was injected from the sampler shoe to lubricate and alleviate friction exerted on the sampling tube as it was pushed into the sand A shutter located at the tip of the samp1er remained open during pushing but forced into a closed position at the end of pushing The closed shutter prevents the sample from falling during withdrawal Upon withdrawal of the sampling tube aboye ground the ends of the tube were sealed and waxed No freezing was applied for the sample preservation An accelerometer was attached to the sampling tube where the acceleration readings were continuously recorded during shipping
VS1 mIs o 100 200 300
o
5 +----------iexcl
10E c o aiexcl
o 15 ---~-------T-- Jiexcliexcl ij traquogt -SCPTU
----- POS Logging
20 iii lSFC=18
A LS FC=43
e LSFC8925
Figure 28 Comparison of laboratory and field Vs1 measurements in YLS with varying fines content
(after Huang and Huang 2007)
89
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
iexclciexcl-iexcl07jono Conl-- LOI [i-_j_ -~iIacute-~ Cec-iexcl~~( iexcl 1 ir i jeE[ cl
water injection
JI
Figure 29 Schematic views ofthe gel-push sampler (after Huang et al 2008)
The soil sample extruded out ofthe gel-push sampler was trimmed to a diameter of70rnm to fit the triaxial testing device and remove a shell of soil that was impregnated by the gel during field sampling Figure 30 compares the V measurements on cyclic triaxial test (CTX) specimens using bender elements and those from the field seismic cane penetration tests (SCPTU) For the most part the laboratory Vs falls within or close to the range of those from SCPTU at comparable depths
Vsmls
100 150 200 250 300
10
--SCPTU
13 +-----m-~b-- ---h CTX
E 16
~ ID
o 19
22
25
Figure 30 Comparison between the Vs measurements from bender elements and thos~ from SCPTU (after Huang et al 2008)
90
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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-
103
GEOTECHNICAl AND GEOPHYSICAl SIlE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
THE CRITICAL STATE APPROACH TO EVALUATE SOIL LIQUEFACTION
In contrast to the semi-empirical field-based methods in simplified procedures the critical state approach to cyclic strength of granular materials has a sound theoretical framework The critical state approach is anchored to the state parameter (ji) The state parameter is the void ratio difference between the current state ofthe soil and the critical state at the same effective mean normal stress (P) The more negative state parameter corresponds to higher soil dilatancy in shearing Figure 31 shows results from cyclic triaxial tests on 13 sands compiled by Jefferies and Been (2006) Consistent with the correlation between state parameter and soil dilatancy the data show that the cyc1ic strength (CRR) increases as ji becomes more negative The state parameter is soil fabric independent The cyc1ic strength however is soil fabric dependent The effects of soil fabric show up when specimens prepared by different methods that result in different cyclic strength (Huang et al 2004) The scatter of test data in Figure 31 is believed to have been caused by variations in soil fabrics originated in different specimen preparation methods involved in the data ofF~ure 31 (Jefferies and Been 2006)
06
05 -1- middotmiddotmiddotmiddotmiddotmiddotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~ bullL
DA -+ ~middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot
~03 middotmiddotmiddottmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot-middotymiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot+middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot Uuml
~~ 1-
02 +middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~middotV ~ ~ 01
O
01 o -01 -02 -03 -OA State parameter V
Figure 31 Cyclic strength as a function of state parameters for 13 sands (after Jefferies and Beeo 2006)
Traditionally studies on the effects of fines on cyclic strength of granular soils have been based on density state (Polito 1999 Thevanayagam et al 2002 and Rahman et al 2008) It can be advantageous to extend the idea of correlating cyclic strength with state parameter into sands with fines The strength inc1uding cyclic strength is a function of density and stress states which are both covered in state parameter Plots between CRR and l from tests from cyclic triaxial tests on reconstituted Mai Liao Sands(MLS) are shown in Figure 32 The specimens were prepared by moist tamping (MT) dry deposition (DD) and water sedimentation (WS) methods The test data generally have coefficients ofcorrelations in excess ofO75 with their corresponding exponential curve fits The range of state parameters shifts significantly towards the positive side that reflects the compressive nature of MLS grains For data of the same specimen preparation group those with high fines contents are clustered towards the positive side of the state parameter axis This is again a reflection of the higher compressibility associated with sand silt mixtures For specimens with the same state parameter CRR of MT specimens are the highest
91
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
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Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
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-
103
and those ofDD specimens are the lowest This is consistent with the earlier findings reported by Huang et al (2004) which indicated that for specimens with the same void ratio CRR from MT specimens are the highest and those from DD specimens are the lowest Therefore in addition to the consideration of stress state the use of state parameter has the additional advantage of reflecting soil grain characteristics These _are desirable features that the concept of density state lacks
06 SPM fe
O MT O CRR=O307exp(-3408P Rl = 0758EB MT 15
0_5 f- + MT 30
O DD O EE DD 15
DD 30 WS O0[ ~ El
2 l WS 15 e u o Itll1gt WS 30 e
03 11 6
+ I ~ o-B+ V )Y~
02 f- +83 Ll~ iexcljJ
4 iexcliexclt(~ o CRR=0224exp(-2653i) -t o R2 = 0752
[gt
Oll~~--~~--~--~~--~~---L--~~~
03 02 01 o -01 -02 -03 State parameter P
Figure 32 Correlation between cyclic strength and state parameter for MLS
Attempts have been made to infer state parameter from in situ tests By analyzing a series of calibration chamber CPT data Been et al (1986 1987) and Jefferies and Been (2006) demonstrated that the normalized cone tip resistance Qp (= (qt-p)p) in log scale has a linear relationship with V as shown in Figure 33 The trend line has a simple exponential form
Qp =kexp( -m1jJ) (15)
This empirically derived equation based on dimensional grounds was consistent with the cavity expansion solution proposed by Carter et al (1986) The values of k and m in Equation (15) correspond respecti vely to the intercept and slope of the trend lines in Figure 33 These values are sand-specific and as such are functions of intrinsic properties of the sands In addition k and m should relate to the slope of the critical state Ene (A)
The validity ofEquation (15) was challenged by Sladen (1989) who indicated that k and possibly m were functions ofp Numerical framework for evaluating V from CPT has been developed (Shuttle and Jefferies 1998 Ghafghazi and Shuttle 2008) This framework was based on cavity expansion analysis and NorSand numerical model Based on their analysis and those of Carter et al (1986) the stress level bias pointed out by Sladen (1989) can be properIy addressed by treating k and m as functions ofrigidity index (Ir) defined as Ir = Gpo Robertson (2010) proposed an empirical chart to estiacutemate V based on Qtn and Fr as shown in Figure 34 According to Robertson the contours ofjl plotted in the Qtn-Fr space are very similar to those ofQ
tnes
92
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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-
103
GEOTECHNICAl ANO GEOPHYSICAl SITE CHARACTERIZATION ORIENTEO TO SEISMIC ANALYSIS
1000 +Montery middotTiacutecino Hokksund
Otlawa Reid Bedford +Hilton Mines -i-Erksak 3553
Syncrude tailings
-Yatesville Silty Sand -o 100 +-Chek Lap Kok ~ West Kowloonoacute=
11 el a
~
10 I
-03 -02 -01 o 01
State para meter 1
Figure 33 The Q -1 trends for different sands (after Jefferies and Been 2006) p
State Pararneter V
rJ If ~ ~ UJ
S ~ j ~
1 10
NORMAUZED menON RAllO Fr
Figure 34 Contours of in Qto-Fr space (Robertson 2010)
Taking advantage of Qp-ji correlation Jefferies and Been (2006) demonstrated the potential of expressing
the liquefaction boundary curve in terms of ji for clean sands Assuming a set of critical state parameters expected for typical clean sands avo = 100kPa and Ko =07 a series ofQp and ji were computed using the critical state based numerical framework and Equation (15) The jI-based boundary curve that separates liquefaction from no liquefaction is a simple exponential function as shown in Figure 35
93
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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-
103
~ 5th iexclniacute~~nQjjonuiexcl C~- l-nicoi ingntOiIIQ
05
middotmiddotmiddotfmiddotmiddotmiddotmiddotmiddotmiddot~-imiddotmiddotmiddotmiddotmiddotmiddotimiddotmiddotmiddotmiddotmiddotmiddotl 04
-+i ~ i03 bull ~ 0 A
o o - ~iexcl ~2 uuml ~ ~~ O A
502 middotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddotmiddot~middot~~middotmiddotmiddotmiddotmiddotiquestrmiddotmiddot=middotmiddotmiddot=middotmiddot=middotmiddot== o ~ ~ --a O O Liquefaction (f) L ~ t deg 0 bull Stark amp Olson 1995 Uuml 1l iexclfJ tgt A
ASuzukietal 1995 ~ 0 No liquefaction
01
deg Stark amp Olson 1995
o I O03exp(-111) A Suzukietal1995
O -01 -02 -03 -04 State parameter l
Figure 35 Liquefaction boundary curve expressed in terms of (after Jefferies amp Been 2006)
Figure 36 shows qt versus p from a set of calibration chamber tests using Da Nang sand For a given state parameter the dilatancy remains constant qt should increase linearly with p The rate of qt increase with p
is k exp( -mljJ) according to Equation (15) This justifies the use of a linear stress normalization of Qp Da Nang Sand is a uniformly graded clean quartz sand with distinct dilatant behavior As shown in Figure 36 there is a consistent correlation between Q and Psimilar to those ofFigure 33 Mai Liao Sand with 15
p
offines on the other hand is relatively compressible The q is much more sensitive to stress than P The t
data points of qt versus P tend to cluster together despite of the variation in P as shown in Figure 37 This phenomenon is also reflected in a poor correlation between Q andP as demonstrated in Figure 38
p
qtMPa o 10 20 30 40 50
O
State Parameter (P)
40 bull -0040 ltgt -0097 bull -0141
80 ~~
O -0184 ~
( -0228~ -p
120
160
200 L ----------------------------~
Figure 36 Increase of qt with p for Da Nang Sand
94
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
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Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
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GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
bull bullbull
GEOTECHNICAL AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANAlYSIS
ltgt
200
~ ~
p 100
cf --
ltgt 50
20~__-L__-L__-L__-L__J-__J-__~__~__~~
-025 -02 -015 -01 -005 o P
Figure 37 Correlation between Qp
and 1 for Da Nang Sand
The critical state approach can have many advantages over the semi-empirical field observation based middotsimplified procedures in liquefaction potential analysis The effects of confining stress on CRR (ie the K
cr
effect) are inc1uded in the CRR-ji correlation The cone tip resistance Q is linear1y normalized with p and p
thus avoids the potential error associated with the exponential stress normalization typically used to obtain Qtn As long as CPT remains drained the fines content is part ofthe soil intrinsic properties (ie grain size gradation mineralogy interpartic1e frietion etc) Their effeets are reflected in the critical state parameters and eoefficients ofk and m Potential eonfusion in the fines content adjustment which is an integral part of the simplified procedure can thus be minimized if not avoided
qtgtMPa O 5 10 15 20 25 30
State Parameter
J O
O bull e
bull -
( fI )
00910+ +e O 0042
bull -0001
bullo
ti) ltgt -0061 e -0127
~ 00 ca~ L -o
2401shy
3201shy bullbull ltgt ltgt
4001L-------------------------------~
Figure 38 Increase of qt with p for Mai Liao Sand
95
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
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Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
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Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
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NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
I [)lh rjefnctOn(l~ CC-I
500--------------~------------~
2001shy ~ I bull l~ lOOmiddot
el
50
20~__J____L__-J____~__~__~__~~~
-02 -Ol O 01 02 P
Figure 39 Correlation between Q and 1 for Mai Liao Sand p
Yu (2004) reported the use ofKD from DMT to infer state parameter as shown in Figure 40 By coupling Figures 35 and 40 Marchetti (2010) experimented the possibility of relating CRR with KD via state parameter The result shown in Figure 41 indicates that the CRR inferred from KD via state parameter tends to be umealistically low If used for liquefaction potential analysis the procedure would yield a rather conservative result Similarly by coupling Figures 35 and 37 it is possible to establish the relationship between CRR and Q p for Da Nang Sand as shown in Figure 42 A comparison with the correlation by Robertson and Wride (1998) (assuming crh = 050 ) also shows that the CRR-Q correlation via state
o vo p
parameter tends to be conservative
161-------------------------------------------------
Hokksund sand bull Kogyuksand
Reid Bredford sand 12 x Ticino sand ~ ~ 8
~
~~ x I
x bull 4 x
O~I____L-__~____~____L____L____~__~L____L____~__~_____L__~
-02 -015 -01 -005 O 005 01 State Pararneter l
Figure 40 Infer state parameter from KD of DMT (Yu 2004)
96
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Ameriacutecan Society for Testing and Materials (ASTM) ASTM Intemational West Conshohocken PA 2003
Andrus R D and Stokoe KH Il (2000) Liquefaction resistance of soils from shear-wave velocity Joumal of Geotechnical and Geoenvironmental Engineering Vol 126 No 11 pp1015 - 1025
Architectural Institute of Japan (AIJ) 2001 Recornmendations for design ofbuilding foundations Baxter C D P Bradshaw A S Green R A and Wang J H (2008) Correlation between cyclic
resistance and shear-wave velocity for Providence silts Joumal ofGeotechnical and Geoenvironmental Engineering Vol 134 No 1 pp 37 - 46
Been K Crooks J F A and Jefferies M G (1986) The cone penetration test in sands part 1 state parameter interpretation Geotechnique Vol 36 No 2 pp 239 - 249
Been K Jefferies M G Crooks J F A and Rothenberg L (1987) The cone penetration test in sands part Il general inferenceofstate Geotechnique Vol 37 No 3pp 285 - 299
BelIoti R Jamiolkowski M Lo Presti D C P and ONeill D A (1996) Anisotropy of small strain stiffness of ticino sand Geotechnique Vol 46 No 1 pp 115 - 131
Bray 1 D and Sancio R B (2006) Assessment ofthe liquefaction susceptibility offine-grainedsoils Joumal of Geotechnical and Geoenvironmental Engineering Vol 132 No 9 pp 1165 - 1177
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
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Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
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and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
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Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
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Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
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Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
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Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
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Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATlON ORIENTED TO SEISMIC ANALYSIS
05 -0-------TT---------
04
~ M~chetti 1)1 ~I L l I ~evna Chameau 1 91
03
~ U
02
01
2 4 6 8 10 Horizontal Stress Index KD
Figure 41 Correlations between CRR and KD ofDMT (after Marchetti 2010)
06 -0-----------------
Robertson amp Wride I
(1998) I
004 ~ I
~ U
I
I
02
CRR = 003exp(-11 P)
OLI__~~___L__~~___L__~~___L~
O 100 200 300 400 500 Qp
Figure 42 Correlations between CRR and Q p
CONCLUDING REMARKS
Significant deveIopments have be en made in fieId testing soil sampling and Iaboratory testing techniques in the past few decades Geotechnical and geophysical site characterization methods are compleinentary to each other Geophysical methods can provide soil stratigraphy elasticsmall strain soil stiffness and dampingattenuation characteristics Nonintrusive geophysical methods are especially attractive for hard-toshysample soils Hybrid or multi-function in situ testing methods such as SCPTU or SDMT enable penetration tests that provide information related to soil stiffness under different strain levels hydraulic conductivity as well as soil stratigraphy Soil samples with reasonable quality can be retrieved under ambient temperature using Laval or gel-push sampler Using local strain measurements deformation and damping characteristics
97
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
REFERENCES
AlIen N F Richart F E Jr and Woods R D (1980) Fluid wave propagation in saturated and nearly saturated sands Joumal ofGeotechnical Engineering Vol 106 No GT3 pp 235 - 254
Ameriacutecan Society for Testing and Materials (ASTM) ASTM Intemational West Conshohocken PA 2003
Andrus R D and Stokoe KH Il (2000) Liquefaction resistance of soils from shear-wave velocity Joumal of Geotechnical and Geoenvironmental Engineering Vol 126 No 11 pp1015 - 1025
Architectural Institute of Japan (AIJ) 2001 Recornmendations for design ofbuilding foundations Baxter C D P Bradshaw A S Green R A and Wang J H (2008) Correlation between cyclic
resistance and shear-wave velocity for Providence silts Joumal ofGeotechnical and Geoenvironmental Engineering Vol 134 No 1 pp 37 - 46
Been K Crooks J F A and Jefferies M G (1986) The cone penetration test in sands part 1 state parameter interpretation Geotechnique Vol 36 No 2 pp 239 - 249
Been K Jefferies M G Crooks J F A and Rothenberg L (1987) The cone penetration test in sands part Il general inferenceofstate Geotechnique Vol 37 No 3pp 285 - 299
BelIoti R Jamiolkowski M Lo Presti D C P and ONeill D A (1996) Anisotropy of small strain stiffness of ticino sand Geotechnique Vol 46 No 1 pp 115 - 131
Bray 1 D and Sancio R B (2006) Assessment ofthe liquefaction susceptibility offine-grainedsoils Joumal of Geotechnical and Geoenvironmental Engineering Vol 132 No 9 pp 1165 - 1177
Burland J B (1989) Small is beautiful-the stiffness of soils at small strains Canadian Geotechnical Joumal Vol 26 No 4 pp 499 - 516
Campanella R G Robertson P K and Gillespie D (1981) In-situ testing in saturated silt (drained or undrained) 34th Canadian Geotechnical Conference Fredericton New Brunswick
Campanella R G Robertson PK and Gillespie D (1986) Sesimic cone penetration test Use of in Situ Tests in Geotechnical Engineering Proceedings In Situ 86 ASCE Geotechnical Specialty Publication No 6 Samuel P Clemence Ced) Balcksburg VA pp 116-130
Campanella R G and Robertson P K (1988) Current status of piezocone test Proc Intemational Symposium on Penetration Testing ISOPT-1 Orlando Vol 1 pp 93-116 Balkema Pub Rotterdam
98
GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
Carter 1 P Booker 1 R and Yeung S K (1986) Cavity expansion in cohesive frictional soils Geotechnique Vol 36 No 3 pp 349 - 358
Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
Huang A B and Hsu H H (2004) Advanced calibration chambers for cone penetration testing in cohesionless soils Proc ISC-2 on Geotechnical and Geophysical Site Characterization Porto Portugal VoLl pp147-167
Huang A B Huang Y T and Ho F J (2005) Assessment of liquefaction potential for a silty sand in Central Western Taiwan Proc XVI ICSMGE Osaka pp 2653 - 2657
Huang A B and Huang Y T (2007) Undisturbed sampling and laboratory shearing tests on a sand with various fines contents Soils and Foundations Vol47 No 4 pp 771 - 781
Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
99
Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
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I r-~Iemcj io- - iexcl-lt-Uumliexcl (
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Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
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Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
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Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
G
that cover a wide range of strains can be measured in laboratory tests on a single specimen With these new developments efficient and cost effective testinganalysis frameworks are available to perforrn geotechnical and geophysical characterization for seismic analysis Essentially all information as outlined by Jamiolkowski and Lo Presti (1995) can be covered under these frameworks The interpretation of in situ index tests for soilliquefaction potential analysis remains empirical It is imperative to calibrate these empirical methods for local soils This is especially true for the case of intermediate soils such as sands with fines The critical state approach appears promising as it has a sound theoretical basisand it is possible to circumvent many of the problems associated with empiacuterical interpretation of in situ tests such as the stress normalization of cone tip resistance The method however needs refinement especially in the context of inferring soil cyclic strength from CPT
AKNOWLEDGEMENTS
Parts ofthe research presented in the paper were funded by the National Sciertce Council ofTaiwan ROC under contracts 97-2221-E-009-128 96-2221-E-009-005 95-2221-E-009-202 and 94-2211shyE-009-043 Field sampling at Kao Hsiung test site was funded by Taiwan Construction Research Institute Taipei Taiwan The authors gratefully acknowledge their support
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Bray 1 D and Sancio R B (2006) Assessment ofthe liquefaction susceptibility offine-grainedsoils Joumal of Geotechnical and Geoenvironmental Engineering Vol 132 No 9 pp 1165 - 1177
Burland J B (1989) Small is beautiful-the stiffness of soils at small strains Canadian Geotechnical Joumal Vol 26 No 4 pp 499 - 516
Campanella R G Robertson P K and Gillespie D (1981) In-situ testing in saturated silt (drained or undrained) 34th Canadian Geotechnical Conference Fredericton New Brunswick
Campanella R G Robertson PK and Gillespie D (1986) Sesimic cone penetration test Use of in Situ Tests in Geotechnical Engineering Proceedings In Situ 86 ASCE Geotechnical Specialty Publication No 6 Samuel P Clemence Ced) Balcksburg VA pp 116-130
Campanella R G and Robertson P K (1988) Current status of piezocone test Proc Intemational Symposium on Penetration Testing ISOPT-1 Orlando Vol 1 pp 93-116 Balkema Pub Rotterdam
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GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
Carter 1 P Booker 1 R and Yeung S K (1986) Cavity expansion in cohesive frictional soils Geotechnique Vol 36 No 3 pp 349 - 358
Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
Huang A B and Hsu H H (2004) Advanced calibration chambers for cone penetration testing in cohesionless soils Proc ISC-2 on Geotechnical and Geophysical Site Characterization Porto Portugal VoLl pp147-167
Huang A B Huang Y T and Ho F J (2005) Assessment of liquefaction potential for a silty sand in Central Western Taiwan Proc XVI ICSMGE Osaka pp 2653 - 2657
Huang A B and Huang Y T (2007) Undisturbed sampling and laboratory shearing tests on a sand with various fines contents Soils and Foundations Vol47 No 4 pp 771 - 781
Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
99
Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL AND GEOPHYSICAL SlrE CHARACTERIZArlON ORIENTED ro SEISMIC ANAlYSIS
Carniel R Malisan P Barazza F and Grimaz S (2008) Improvement ofHVSR technique by wavelet analysis Soil Dynamics and Earthquake Engineering Vol 28 pp 321 - 327
Carter 1 P Booker 1 R and Yeung S K (1986) Cavity expansion in cohesive frictional soils Geotechnique Vol 36 No 3 pp 349 - 358
Cavallaro A Grasson S and Maugeri M (2006) Clay soil characteristics by the new seismic dilatometer Marchetti test (SDMT) Proc 2nd International Conference on the Flat Dilatometer (DMT2006) pp261-268
Cetin K O and Isik N S (2007) Probabilistic assessment of stress normalization for CPT data Journal ofGeotechnical and Geoenvironmental Engineering Vo1133 No7 pp887-897
Cetin K O Seed R B Kjureghian A D Tokimatsu K Harder L F Kayen R E and Moss R E S (2004) Standard penetration test-based probabilistic and deterministic assessment of seismic soil liquefaction potential Journal of Geotechnical and Geoenvironmental Engineering Vol 130 No 12 pp 1314-1340
Dobry R Ladd R S Chung R M and Powell D (1982) Prediction ofpore water prersure buildup and liquefaction of sands during earthquakes by the cyclic strain method N ational Bureau of Standards Building Science Series 138
Dyvik R and Madshus C (1985) Laboratory measurement of Gmax using bender element Proc AS CE Annual Convention Advance in the art oftesting spils under cyc1ic conditions Detroit pp 186 - 196
Fahey M (1998) Deformation and in situ stress measurement Proc 1 st International Conference on Geotechnical Site Characterization (ISC-1) Atlanta USA pp49-68
Ghafghazi M and Shuttle D (2008) Interpretation of sand state from cone penetration resistance Geotechnique Vol 58 No 8 pp 623 - 634
Goto S Tatsuoka F Shibuya S Kim Y~S and Sat() T (1991) A Simple gauge for local small strain measurements in the laboratory Soils and Foundations Vol 31 No 1 pp 169 - 180
Harder LF Jr and Seed HB (1986) Determination of penetration resistance for coarse grained soils using the Becker harnmer drill Rep USBEERC-8606 Earthquake Engineering Research Center University of California at Berkeley
H0eg K Dyvik R and Sandbekken G (2000) Strength of undisturbed versus reconstituted silt and silty sand specimens Journal of Geotechnical and Geoenvironmental Engineering Vol 126 No 7 pp 606 - 617
Hofmann BA (1997) In situ ground freezing to obtain undisturbed samples ofloose sand for liquefaction assessment PhD thesis Department of Civil and Environmental Engineering University of Alberta Edmonton Alberta Canada
Hofmann B A Sego D C and Robertson P K (2000) In situ ground freezing to obtain undisturbed samples ofloose sand Canadian Geotechnical Journal Vol 126 No 11 pp 979 - 989
Huang Y T Huang A B Kuo Y C and Tsai M D (2004) A laboratory study on the undrained strength ofa silty sand from Central Western Taiwan Soil Dynamics and Earthquake Engineering Vol 24 No 9-10 pp 733 - 743
Huang A B and Hsu H H (2004) Advanced calibration chambers for cone penetration testing in cohesionless soils Proc ISC-2 on Geotechnical and Geophysical Site Characterization Porto Portugal VoLl pp147-167
Huang A B Huang Y T and Ho F J (2005) Assessment of liquefaction potential for a silty sand in Central Western Taiwan Proc XVI ICSMGE Osaka pp 2653 - 2657
Huang A B and Huang Y T (2007) Undisturbed sampling and laboratory shearing tests on a sand with various fines contents Soils and Foundations Vol47 No 4 pp 771 - 781
Huang A B Tai Y Y Lee W F and Ishihara K (2008) Sampling and field characterization of the silty sand in Central and Southern Taiwan Proc 3rd International Conference on Site Characterization (ISC-3) Taipei Taylor amp Francis pp 1457 - 1463
99
Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
Huang A B (2009) Lessons leamed from sampling and CPT in siltsand soils Intemational Conference on Performance-Based Design in Earthquake Geotechnical Engineering - from case history to practice Tokyo
Huang A B Tai Y Y Lee W F and Huang Y T (2009) Fie1d evaluation ofthe cyclic strength versus cone tip resistance corre1ation in silty sands Soi1s and Foundations Vol 49 No 4 pp 557-568
Idriss 1 M and Boulanger R W (2006) Semi-empirica1 procedures for evaluating liquefaction potential during earthquakes Soi1 Dynamics and Earthquake Engineering Vol 26 pp 115 - 130
Ishihara K (1993) Liquefaction and flow failure during earthquakes Geotechnique Vol 43 No 3 pp 351 - 415
Ishihara K (1996) Soil behaviour in Earthquake Geotechnics Oxford University Press Inc New York Ishihara K and Harada K (2008) Effects of lateral stress on relations between penetration resistances
and cyclic strength to liquefaction Proc 3rd Intemational Conference on Site Characterization (ISCshy3) Taipei pp 1043 - 1050
Iwasaki T and Tatsuoka F (1977) Effects of grain size and grading on dynamic sfiear modulus ofsands Soils and Foundations Vol 17 No 3 pp 19 - 35
Jamiolkowski M Lo Presti D C F and Pallara O (1995) Role of in situ testing in geotechnica1 earthquake engineering Proc Third Intemationa1 Conference on Recent Advances in Geotechnica1 Earthquake Engineering and SoU Dynamics State of the Art 7 St Louis Missouri April 2-7 1995 vol II pp 1523 - 1546
Japan Road Association (JRA) (1996) Specifications for Highway Bridges Part III Seismic designo Jardine R J (1992) Sorne observations on the kinematic nature ofsoi1 stiffness Soi1s and Foundations
Vol 32 No 2 pp 111 - 124 J efferies M G and Been K (2006) Soilliquefaction - A critical state approach Taylormiddotand Francis Juang C H Jiang T and Andrus R D (2002) Assessing probability-based methods for liquefaction
potential evaluation Jouma1 of Geotechnica1 and Geoenvironmenta1 Engineering Vol 128 No 7 pp 580 - 589
Juang C H Fang S Y and Khor E H (2006) First-order reliability method for probabilistic 1iquefaction triggering analysis using CPT Jouma1 ofGeotechnica1 and Geoenvironmental Engineering Vol 132 No 3 pp 337 - 350
Kause1 E and Roesset J M (1981) Stiffness matrices for 1ayered soils Bulletin of the Seism010gical Society ofAmerica Vol 71 NO 6 pp 1743 - 176l
Kokusho T (1980) Cyclic triaxia1 test of dynamic soi1 properties for wide strain range Soils and Foundations Vol 20 No 2 pp 45 - 60
Konrad J M St-Laurent S Gi1bert F and Lerouei1 S (1995) Sand sampling below the water table using the 200 mm diameter Laval sampler Canadian Geotechnica1 Jouma1 Vol 32 pp 1079 - 1086
Kotani N Ishihara K Imamura S Hagiwara T and Tsukamoto Y (2002) Centrifuge experiments on group pi le effects under lateral ll0vement ofliquefied ground ProC JSCE Annua1 Conference 57 pp 1243 - 1244 (in Japanese)
La Rochelle P Sarrai1h 1 Tavenas F Roy D and Larouei1 S (1981) Causes ofsamp1ing disturbance and design of a new samp1er for sensitive soi1s Canadian Geotechnical Joumal Vol 18 No 1 pp 52 - 66
Landon M M DeGroot D 1 and Sheahan T C (2007) Nondestructive sample quality assessment of a soft c1ay using shear wave ve1ocity Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 133 No 4 pp 424 - 432
Marchetti S (1980) In situ tests by F1at Di1atometer J ouma1 of Geotechnica1 Engineering Vol 106 No GT3 pp 299 - 32l
Marchetti S (1982) Detection of 1iquefiab1e sand 1ayers by means of quasi-static penetration probes ESOPT II Amsterdam Vol 2 pp 689 - 695
100
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
Mayne P W Christopher B R and DeJong J (2002) Subsurface Investigations - Geotechnical Site Characterization Reference Manual US Department of Transportation Federal Highway Administration
Mayne PW Coop MR Springman SM Huang AB Zornberg JG (2009) Geomaterial behavior and testing Proc XVII ICSMGE Alexandria Egypt Vol 4 pp 2777 - 2872
McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
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103
GEOTECHNICAl AND GEOPHYSICAl SITE CHARACTERIZATION ORIENTED TO SEISMIC ANAlYSIS
Marchetti D Marchetti S Monaco P and Totani G (2008) Experience with Seismic Dilatometer (SDMT) in various soil types Proc 3rd International Conference on Geotechnical and Geophysical Site Characterization (ISC-3) Taipei Taiwan
Marchetti S (2010) Sensitivity of CPI and DMI to stress history and aging in sands for liquefaction assessment Proc CPT 10 (wwwcptlOcom) Huntington Beach California
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McNeilan T W and Bugno W T (1984) Cone penetration test results in offshore California silts Symposium on Strength Testing of Marine Sediments Laboratory and In-Situ Measurements San Diego ASTM STP 883 pp55-7l
Monaco P Marchetti S Totani G and Calabrese M (2005) Sand liquefiability a~essment by Flat Dilatometer Test (DMT) Proc XVI ICSMGE Osaka Vol 4 pp 2693 - 2697
Moss R E S Seed R B and Olen R S (2006) Normalizing the CPT for overburden stress Journal of Geotechnical and Geoenvironmental Engineering Vol 132 No 3 pp 378 - 387
Nakamura Y (1989) A method for dynamic characteristic estimation of subsurface using microtremor on the ground surface Q Rep RaiIway Tech Res Inst Vol 30 No 1 pp 25 - 33
Nigbor R L and Imai T (1994) The suspension P-S velocity logging method Geophysical Characteristics of Sites ISSMFE Technical Committee 10 for XIII ICSMFE International Science Publishers New York pp 57-63
NRC (2000) Seeing into the Earth Committee for Noninvasive Characterization of the Shallow Subsurface for Environmental and Engineering Applications PR Romig Chair
Park C B Miller R D and Xia J (1999) Multichannel analysis of surface waves Geophysics Vol 64 No 3 pp 800 - 808
Po lito C P (1999) The effects of nonplastic and plastic fines on the liquefaction of sandy soils PhD Thesis Virginia Polytechnic Institute and State University Blacksburg Virginia
Rahman M M Lo S R and Gnanendran C T (2008) On equivalent granular void ratio and steady state behavior of loose sand with fines Canadian Geotechnical J ournal Vol 45 pp1439 - 1456
Reyna F and Chameau J L (1991) Dilatometer based liquefaction potential of sites in the Imperial Valley Proc 2nd Int Conf on Recent Advances in Geot Earthquake Engrg and Soil Dyn St Louis pp 385 - 392
Richart F E Hall J R and Woods R D (1970) Vibrations of SoiIs and Foundations Prentice Hall Eglewood Cliffs
Robertson P K and Campanella R G (1986) Estimating liquefaction potential of sands using the flat plate dilatometer Geotechnical Testing Journal Vol 9 No 1 pp 38 - 40
Robertson P K Sully J O Woeller D J Lunne T Powell J J M and Gillespie (1992) Estimating coefficient of consolidation from piezocone tests Canadian Geotechnical Journal Vol 29 pp 539 shy550
Robertson P K and Wride C E (1998) Evaluating cyc1ic liquefaction potential using the cone penetration test Canadian Geotechnical Journal Vol 35 pp 442 - 459
Robertson P K (2009) Interpretation of cone penetration tests - a unified approach Canadian Geotechnical Journal Vol 46 pp 1337 - 1355
Robertson P K (2010) Evaluation of flow liquefaction and liquefied strength using the c~ne penetration test Journal of Geotechnical and Geoenvironmental Engineering Vol 136 No 6 pp 842 - 853
Robertson P K (2010) Estimating state parameter and friction angle in sandy soils from CPT Proc CPTlO (wwwcptlOcom) Huntington Beach California
101
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
I r-~Iemcj io- - iexcl-lt-Uumliexcl (
Rollins K Evans M Diehl N and Daily W (1998) Shear modu1us and damping relationships for gravels Journal of Geotechnical and Geoenvironmental Engineering Vol 124 No 5 pp 396 - 405
Roy D (2008) Coupled use of cone tip resistance and small strain shear modulus to assess liquefaction potential Journal ofGeotechnical and Geoenvironmenta1 Engineering Vo1134 No 4 pp 519 - 530
Seed H B and Idriss I M (1971) Simplified procedure for evaluating soi11iquefaction potential Journal ofSoil Mechanics Division Vol 97 No SM9 pp 1249 - 1273
Seed H B (1979) Soil1iquefaction and cyclic mobility evaluation for 1evel ground during earthquakes Journa1 ofthe Geotechnical Engineering Division Vol 105 No GT2 pp 201 - 255
Seed H B Tokimatsu K Harder Jr L F and Chung R (1984) The influence ofSPT procedures on soil liquefaction resistance eva1uations Report No UCBEERC-84115 University of California Berke1ey
Seed H B Tokimatsu K Harder LF and Chung RM (1985) Influence of SPT procedures in soil liquefaction resistance evaluation Journal of Geotechnical Engineering Vol 111 No 2 pp 1425 -1445
Scho1ey G K Frost 1 D Lo Presti D C F and Jamio1kowski M (1995) Instrumiquestntation for measuring local strains during triaxial testing of small specimens ASTM Geotechnical Testing Journal Vol 18 No 2 pp 137 - 156
Sheriff R E and Geldart L P (1995) Exploration Seismology 2nd edition Cambridge University Press lnc
Shuttle D A and Jefferies M G (1998) Dimensionless and unbiased CPT interpretation in sand International Journal ofNumerical and Ana1ytica1 Methods in Geomechanics Vol 22 pp 351 - 391
Singh S Seed H B and Chan C K (1982) Undisturbed sampling of saturated sands by freezing Journal ofthe Geotechnical Engineering Division Vol 108 No 2 pp 247 - 264
Sladen 1 A (1989) Prob1ems with interpretation of sand state from cone penetration test Geotechnique Vol 39 No 2 pp 323 - 332
Stark T D and Olson S M (1995) Liquefaction resistance using CPT and field case histories Journal ofGeotechnical Engineering Division Vol 121 No 12 p 856 - 869
Stokoe K H II and Nazarian S (1985) Use ofRayleigh waves in liquefaction studies Proceedings Measurement and Use of Shear Wave Velocity for Evaluating Dynamic Soil Properties Geotechnical Engineering Division ASCE pp 1 - 17
Stokoe K H JI and Santamarina J C (2000) Seismic-wave based testing in geotechnical engineering Plenary Paper Intemational Conference on Geotechnical and Geological ir Engineering GeoEng 2000 Melboume Australia pp1490 - 1536
Stokoe K H JI Joh S H and Woods R D (2004) Sorne contributions ofin situ geophysical measurements to solving geotechnical engineering prob1ems Proceedings ISC-2 on Geordmt~chnical andf Geophysical Site CharacterizationMillpress Rotterdam - -
Susuki Y Tokimatsu K Koyamada K Taya Y and Kubota Y (1995) Field correlation of soil liquefaction based on CPT data Proc International Symposium on Cone Penetration Testing CPT95 Vol 2 pp 583 - 588
Tani K and Kaneko S (2006) Method of recovering undisturbed samples using water-soluble thick polymer Tsuchi-to-Kiso Journal of JapaneseGeotechnical Society Vol 54 No 4 pp 145 - 148 (in Japanese)
Thevanayagam S Shenthan T Mohan S and Liang J (2002) Undrained fragility of clean sands silty sands and sandy silts Journal of Geotechnical and Geoenvironmental Engineering Vol 128 No 10 pp 849 - 859 --
Thevanayagam S and Martin G R (2002) Liquefaction in silty soils - screening and remediation issues Soil Dynamics and Earthquake Engineering Vol 22 pp 1035 - 1042
Toki S Shibuya S and Yamashita S (1995) Standardization of laboratory test methods to determine the cyclic deformation properties of geomaterials in Japan Proc 1 st Pre-Failure Deformation of Geomaterials Sapporo Japan Vol 2 pp 741 - 784
102
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
-
103
GEOTECHNICAL ANO GEOPHYSICAL SITE CHARACTERIZATlON ORIENTED ro SEISMIC ANAL YSIS
Tokimatsu K Suzuki Y Taya Y and Kubota Y (1995) Correlation between liacutequefaction resistance of in-situ frozen samples and CPT resistance Proc 10th Asiacutean Regional Conference on Soil Mechanics amp Foundation Engineering Beijing pp 493 - 496
Wang Y and ORourke T D (2007) Interpretation of secant shear modu1us degradation characteristics from pressuremeter tests Joumal of Geotechnical and Geoenvironmental Engineering Vol 133 No 12 pp 1556 - 1566
Yamamuro J A and Covert K M (2001) Monotonic and cyc1ic liquefaction of very lose sands with high silt content Joumal of Geotechnical and Geoenvironmenta1 Engineering Vol 127 No 4 pp 314 - 324
Yoshimi Y Hatanaka M and Oh-Oka H (1977) A simple method for undisturbed sand sampling by freezing Proc 9th Intemationa1 Conference on Soi1 Mechanics and Foundation Engineering Specia1 Session 2 Tokyo Japan pp 23 - 28
Youd T L et al (2001) Liquefaction resistance ofsoi1s surnmary report from the 1996 NCEER and 1998 NCEERNSF workshops on eva1uation ofliquefaction resistance of soils Joumal of6eotechnical and Geoenvironmental Engineering Vol 127 No 10 pp 817 - 833
Yu H S (2004) In situ soil testing from mechanics to interpretation 1st J K Mitchell Lecture Proc 2nd Int Conf on Site Characterization ISC-2 Porto Vol 1 pp 3 - 38
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103