ground liquefaction
DESCRIPTION
concepts of ground LiquefactionTRANSCRIPT
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Building design: Buildings that are not
designed for earthquake loads suffer
more
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no significant structural damage occurred, even glass is intact
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The solid building tilted as a rigid body and the raft
foundation rises above the ground.
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Nepal Bihar 1934
Narrow escape of Tinsukia Mail Hanginging railway track
Burma-India earthquake 1988
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Sand blow in mud flats used for salt production southwest of Kandla Port, Gujarat
Sand Boil: Ground water rushing to the surface due to liquefaction
JAPAN GREAT EQ 2011
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Wide open cracks showing prominent
displacement affecting the Malya-Bhuj
road near Surajbadi. This is an example
of 'lateral spread' consequent to
earthquake induced liquefaction of the
underlying marshy tract of Gulf of
Kutch
Lateral spreading due to
liquefaction leading to
submergence of part of rail-road
embankment in the Gulf of Kutch
near Naolakhi Port.
EFFECTIVE DAMAGE DUE TO LIQUEFACTION Cont…
2011 JAPAN EQ
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2011 JAPAN EQ
Predicting Liquefaction Resistance
Design of new structures
Retrofitting of existing structures
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Liquefied soil has residual strength
and exhibits complexStress-strain behavior
3.16 LIQUEFACTIONLiquefaction is a state (primarily) in saturated
cohesionless soil wherein the effective shear
strength is reduced to negligible value for all
engineering purpose due to pore pressure caused
by vibrations during an earthquake when they
approach the total confining pressure. In this
condition the soil tends to behave like a fluid
mass.
IS:1893-Part-I
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Liquefaction Susceptibility of Gravels.
(WSDOT Geotechnical Design Manual)
*No specific guidance regarding susceptibility of gravels
to liquefaction is currently available.
*The primary reason why gravels may not liquefy is that
their high permeability frequently precludes the
development of undrained conditions during and after
earthquake loading.
*When bounded by lower permeability layers,
however, gravels should be considered susceptible to
liquefaction and their liquefaction potential evaluated.
*A gravel that contains sufficient sand/silt to reduce its
permeability to a level near that of the sand, even if not
bounded by lower permeability layers, should also be
considered susceptible to liquefaction
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6.3.5.2, Page 14 of IS:1893-Part-I
In soil deposits consisting of submerged loose sands
and soils falling under classification SP with standard
penetration N-values less than 15 in seismic Zones
III, IV, V and less than 10 in seismic Zone II, the
vibration caused by earthquake may cause liquefaction
or excessive total and differential settlements.
• Such sites should preferably be avoided while locating
new settlements or important projects.
• Otherwise, this aspect of the problem needs to be
investigated and appropriate methods of compaction
or stabilization adopted to achieve suitable N-values
as indicated in Note 3 under Table 1. (next slide)
• Alternatively, deep pile foundation may be provided
and taken to depths well into the layer which is not
likely to liquefy.
Note 3.Desirable minimum field values of N are as follows—
Note 4 The above values of N (corrected values) are at the
founding level and the allowable bearing pressure shall be
determined in accordance with IS 6403 or IS 1888.
For values of depths between 5 m and 10 m, linear interpolation is recommended
Note 3 under Table 1
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4. Marine clays and other sensitive clays are
also known to liquefy due to collapse of soil
structure and will need special treatment
according to site condition.
NOTE — Specialist literature may be referred for
determining liquefaction potential of a site.
If soils of smaller N-values are met, compaction may
be adopted to achieve these values or deep pile
foundations going to stronger strata should be used.
2011 JAPAN EQ
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•The piles should be designed for
lateral loads neglecting lateral
resistance of soil layers liable to
liquefy.
IS:1893-Part-I
2011 JAPAN EQ
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COLLAPSE OF PILED STRUCTURES IN EARTHQUAKES
Million Dollar Bridge after 1964Alaska earthquake
Showa Bridge after 1964
Niigata earthquake
Building in Kobe after
1995 earthquake
1964
19951999 2001
Bridge in Taiwan after 1999
Chi-Chi earthquake Kandla port building after
2001 Bhuj earthquake
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Suitably intense earthquake shakes
Loose, saturated sand
Grain structure tends to consolidate to more compact
packing
Process being very rapid
No pore water pressure dissipation
Effective stress becomes zero
Deposit liquefies
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Liquefaction
Most importantInterestingComplexControversial
Soil deformations caused by
Monotonic
TransientRepeated disturbances
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Liquefaction Susceptibility
Historical CriteriaGeologic Criteria
Compositional CriteriaState Criteria
(stress and density)
Liquefaction Zones are areas meeting one
or more of the following:
1. Areas where liquefaction has occurred during
historical earthquakes.
2 . Areas of un-compacted or poorly compacted fills
containing liquefaction-susceptible materials that
are saturated, nearly saturated, or may be expected
to become saturated.
3. Areas where sufficient existing geotechnical data
and analyses indicate that the soils are potentially
susceptible to liquefaction.
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4. For areas where geotechnical data are lacking zones are delineated using one or more of the following criteria:
• a) Areas containing soil of late Holocene age (less than 1,000 years old, current river channels and their historical flood plains, marshes, and estuaries) where the groundwater is less than 40 feet (12.2 m) deep and the anticipated earthquake peak ground acceleration (PGA) having a 10% probability of being exceeded in 50 years is greater than 0.1g.
• b) Areas containing soils of Holocene age (less than 11,000 years old) where the groundwater is less than 30 feet (9.2 m) below the surface and the PGA (10% in 50 years) is greater than 0.2g.
• c) Areas containing soils of latest Pleistocene age (11,000 to 15,000 years before present) where the groundwater is less than 20 feet (6.1 m) below the surface and the PGA (10% in 50 years) is greater than 0.3g.
Quantitative evaluation of
liquefaction hazard potential is not required:
• If the estimated maximum-past-, current-, andfuture-ground-water-levels are determined to bedeeper than 15m below the existing ground surfaceor proposed finished grade liquefaction assessmentsare not required.
• For shallow foundations , liquefaction evaluationmay be omitted when the saturated sandy soilsare found at depths greater than 15 m. (Eurocode8)
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EARTHQUAKE SAFE CONSTRUCTION OF MASONRY BUILDINGS:
Simplified Guideline for All New Buildings in the
Seismic Zone V ( & IV)
of India by P r e p a r e d b y : Professor Anand S. Arya and Jnananjan Panda,
for National Disaster Management Division, Prepared under the GoI – UNDP
Disaster Risk Management Programme
• In sandy soils with high water table within
8m (5m for zone III) depth below ground
level, which may get liquefied during
earthquake of MSK intensity VIII to IX,
(MSK intensity VIII, for zone IV, MSK
intensity VII, for zone III) pile foundation
need to be used in consultation with the
Structural/ Geotechnical Engineer.
Quantitative evaluation of
liquefaction hazard potential is not required:
• If the corrected standard penetration blow count, (N1)60, is greater than or equal to 30 in all samples of clean sands with a sufficient number of tests, liquefaction assessments are not required.
• If cone penetration test soundings are made, the corrected cone penetration test tip resistance, qc1N, should be greater than or equal to 160 in all soundings in sand materials.
• depth-corrected normalized cone penetration
resistance values qc1N > 175, or stress-corrected shear
wave velocity VS1 > 230 m/sec (755 ft/sec) are
considered of sufficient density to pose little risk of
liquefying.
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Seed et al, 1985, state
• that soil layers with a normalized SPT blow
count [(N1)60] less than 22 have been known
to liquefy.
• Marcuson et al, 1990, suggest an SPT value
of [(N1)60] less than 30 as the threshold to
use for suspecting liquefaction potential.
Liquefaction has also been shown to occur
if the normalized CPT cone resistance (qc)
is less than 157 tsf (15 Mpa) (Shibata and
Taparaska, 1988).
• EURO CODE 8 –part5
• (8) The liquefaction hazard may be neglected when α⋅S < 0,15 and at least one of the following conditions is fulfilled:
• - the sands have a clay content greater than 20% with plasticity index PI > 10;
• - the sands have a silt content greater than 35% and, at the same time, the SPT blow count value normalised for overburden effects and for the (N1)60
> 20;
• - the sands are clean, with the SPT blow count value normalised for overburden effects and for the energy ratio (N1)60 > 30.
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Evaluation of Liquefaction
Susceptibility
Cyclic Stress
Approach
CyclicStrain
Approach
Other approaches :
Energy Dissipation,
Probabilistic approach etc.
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Cyclic Stress Approach
Earthquake Loading Cyclic Shear stresses
Liquefaction resistance Cyclic shear stresses
Loading > Resistance Liquefaction occurs
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Cyclic Stresses Induced
Cyclic resistance Available
• Laboratory Testing
• Field Testing
Characterization of Earthquake Loading
amax =PEAK GROUND ACCELERATION
Stresses Induced in the Soil
g = Acceleration due to gravity; = Unit weight of soil
maxmax .ag
h
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h
max=(h/g)amax
h
Maximum Shear Stress at a Depth for a Rigid Soil Column
amax
maxmaxmax .. ag
hrr ddact
rd = Stress reduction factor
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dav rag
hmax65.0
Seed and Idriss (1971) formulated the following equation for
calculation of CSR:
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Evaluation of Liquefaction Resistance
Laboratory Tests Dynamic/Cyclic Triaxial Tests Cyclic Simple Shear Tests
Field Tests SPT CPT Shear Wave Velocity BPT
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Field Testing
Depositional and environmental history is
preserved
SPT
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This equation is valid for (N1)60 less than 30 and may be used in
spreadsheets.
Thomas F. Blake (Fugro-West, Inc., Ventura, Calif., written
commun.) approximated the simplified base curve plotted on
Figure 2 by the following equation 4:
where CRR7.5 is the cyclic resistance ratio for magnitude 7.5
earthquakes; x = (N1)60; a = 0.048; b = -0.1248; c = -0.004721;
d = 0.009578; e = 0.0006136; f = -0.0003285; g = -1.673E-05; and
h = 3.714E-06.
This equation 4 is valid for (N1)60 less than 30 and may be used in
spreadsheets.
Robertson and Wride (this report) indicate that Equation 4 is not
applicable for (N1)60 less than three.
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where Nm is the measured standard penetration resistance,
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Pa=100kPa
The advantages of using the SPT to evaluate the liquefaction potential are as
follows:
Groundwater table: A boring must be excavated in order to perform
the standard penetration test. The location of the groundwater table can be
measured in the borehole, which can then be used to monitor the ground
water level over time.
Soil Type: In clean sand, the SPT sampler may not be able to retain a
soil sample. But for most other types of soil, the SPT sampler will be able to
retrieve a soil sample. The soil sample retrieved in the SPT sampler can be
used to visually classify the soil and to estimate the percent fines in the soil.
Relationship between N value and liquefaction potential: In general,
the factors that increase the liquefaction resistance of a soil will also increase
the N from the SPT. There have been plenty of case histories dealing with N
values and liquefaction dating back from the time of Nigata earthquake.
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FS= (CRR7.5/CSR). MSF. Kσ . Kα
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Revised Seed magnitude scaling factor is
Atmospheric pressure Pa = 100 kPa =1 atm
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Zone of liquefaction in the field
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EUROCODE 8 PART5
If the field correlation approach is used, a soil shall be
considered susceptible to liquefaction under level ground
conditions whenever the earthquake-induced shear
prEN 1998-5:2003 (E)18 stress exceeds a certain fraction λ
of the critical stress known to have caused liquefaction in
previous earthquakes.
NOTE The value ascribed to λ for use in a Country may be
found in its National Annex.
The recommended value is λ = 0.8, which implies a safety
factor of 1.25.
As a final comment on the assessment of liquefaction
hazards, it is important to note that soils composed of
sands, silts, and gravels are most susceptible to
liquefaction while clay soils generally are not
susceptible to this phenomenon.
The curves in Figure 4 are valid for soils composed
primarily of sand.
The curves should be used with caution for soils with
substantial amounts of gravel. Verified corrections for
gravel content have not been developed; a geotechnical
engineer, experienced in liquefaction hazard
evaluation, should be consulted when gravelly soils are
encountered.
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