dr omar hamza foundation engineering ce 483 2. site investigations copy right reserved to dr o....
TRANSCRIPT
Dr O
mar
Ham
za
Foundation EngineeringCE 483
2. Site Investigations
Copy
righ
t res
erve
d to
Dr O
. Ham
za
Contents– Introduction– Program of site investigation– Planning– Implementation– Reporting
CE 483 - Foundation Engineering - 2. Site Investigation
Dr O
mar
Ham
za
3
Introduction
CE 483 - Foundation Engineering - 2. Site Investigation
What is Site Investigation (SI)? Why Site Investigation? Objectives of Site Investigation
Copy
righ
t res
erve
d to
Dr O
. Ham
za
4
Introduction
What is site investigation (SI)?
The design of foundations of structures (such as buildings, bridges, and dams) generally requires information about:
Structure
Ground
• Structure• Ground
CE 483 - Foundation Engineering - 2. Site Investigation
5
Introduction
• Site investigation (SI) or soil exploration is the process of gathering information, within practical limits, about the stratification (layers) and engineering properties of the soils underlying the proposed construction site.
Structure
GroundSite Investigation
Bore
hole
What is site investigation (SI)?
Layers
• The principal engineering properties of interest are the strength, deformation, and permeability characteristics.
Drilling rig
6
Introduction
Why site investigation (SI)?
CE 483 - Foundation Engineering - 2. Site Investigation
• Many engineering failures could have been avoided if a proper site investigation had been carried out.
Sinkhole
The site has a sinkhole risk which might have
been discovered in a proper site investigation
7
Introduction
Why site investigation (SI)?
CE 483 - Foundation Engineering - 2. Site Investigation
Sophisticated theories alone will not give a safe and sound design.
• The success or failure of a foundation depends essentially on the reliability of the knowledge obtained from the site investigation.
8
Introduction
Objectives of site investigationThe knowledge about the ground of the proposed construction site is obtained by Site Investigation, and used to determine:
Suitability: of site for the proposed
construction? Type of design solution: e.g.
type of foundation:
shallow or deep.Design parameters:
such as strength,
compressibility, permeability &
other parameters
used for geotechnical
design
Ground or Ground-water
conditions: that would affect the
design and construction? e.g. expansive soil, collapsible
soil, high ground water…
Geo-materials: available on site which can be re-
used?
Effect of changes: How will the design affect adjacent properties and
the ground water?
Site
Inve
stiga
tion
9
Introduction
Objectives of site investigation
Suitability: of site for the proposed
construction? Type of design solution: e.g.
type of foundation:
shallow or deep.Design parameters:
such as strength,
compressibility, permeability &
other parameters
used for geotechnical
design
Ground or Ground-water
conditions: that would affect the
design and construction? e.g. expansive soil, collapsible
soil, high ground water…
Geo-materials: available on site which can be re-
used?
Effect of changes: How will the design affect adjacent properties and
the ground water?
Site
Inve
stiga
tion
Manage the geotechnical risk
CE 483 - Foundation Engineering - 2. Site Investigation
10
Program of site investigation
CE 483 - Foundation Engineering - 2. Site Investigation
Before Site Investigation The sequence of Site Investigation
Dr O
mar
Ham
za
11
Program
Before Site Investigation• Site Investigation is usually carried out as part of Subsurface Exploratory
program. • Before conducting the Site Investigation, the program usually include: Desk
Study and Site Reconnaissance.
Desk Study Collect and review preliminary information about the site, and the structure to be built.
Site ReconnaissanceVisual inspection of the site.
CE 483 - Foundation Engineering - 2. Site Investigation
12
Collecting general information about the structure, from the architectural and structural design:
Structure
Ground
Information about the Structure– Type, dimensions, and use of the structure,
and any special architectural considerations. – the load that will be transmitted by the
superstructure to the foundation system– the requirements of the local building code
(e.g. allowable settlement)
Program
Desk Study Before Site Investigation
CE 483 - Foundation Engineering - 2. Site Investigation
13
Collecting general information about the ground, from already existing data such as: geological maps, seismic maps, Ariel Photography, Services records (Gas, Water, Electricity), Previous geo-environmental or geotechnical reports, … etc. at or near site.
Structure
Ground
Program
Desk Study Before Site Investigation
Information about the ground:– the geological conditions of the ground (e.g.
layers, Geological features, Ground water, Flood & Earthquake risk in the area, ..).
– the historical use of the site – if previously used as quarry, agricultural land, industrial unit with contamination issue, man-made fill/slope, etc.
CE 483 - Foundation Engineering - 2. Site Investigation
14CE 483 - Foundation Engineering - 2. Site Investigation
Ariel Photograph taken for a site – shows a possible sinkhole
15
Program
Site Reconnaissance
The Site Reconnaissance is normally in the form of a walk-over survey of the site.
Before Site Investigation
CE 483 - Foundation Engineering - 2. Site Investigation
What things do I need to
look for?
Engineer during Site Visit
Dr O
mar
Ham
za
16
Program
Site ReconnaissanceImportant evidence to look for is:
Before Site Investigation
1. Stratification of soil: from deep cut, such as those made for the construction of nearby highway or other projects – if any.
2. Slope: signs of slope instability include bent trees, shrinkage cracks on the ground and displaced fences or drains.
Stratification of soil Signs of slope instability
17
Program
Site ReconnaissanceImportant evidence to look for is:
Before Site Investigation
3. Structures: type of buildings in the area and the existence of any cracks in walls or other problems. You may need to ask local people.
Tipping settlement (often without cracks)
Differential settlement (with cracks)
Indication of possible ground-related problem
CE 483 - Foundation Engineering - 2. Site Investigation
18
Program
Site ReconnaissanceOther important evidence to look for is:
Before Site Investigation
4. Mining: The presence of previous mining is often signs of subsidence and possibly disused mine shafts. Open cast mining is indicated by diverted streams replaced or removed fence/hedge lines.
5. Hydrogeology: Wet marshy ground, springs or seepage, ponds or streams and Wells.
6. Topography: possible existence of drainage ditches or abandoned debris or other man-made features.
7. Vegetation: may indicate the type of soil.8. Access: It is essential that access to the site can be easily obtained.
Possible problems include low overhead cables and watercourses.
CE 483 - Foundation Engineering - 2. Site Investigation
19
Program
The sequence of Site Investigation
• Whether investigation is preliminary or detailed, there are three important phases:
planning, implementation and reporting.
Planning
Implementation
Reporting
• In large construction projects, 2 site investigations (SI) are carried out: – Preliminary SI, followed by – Detailed SI.
• Soil exploration is a requirement for the design of foundations of any project.
CE 483 - Foundation Engineering - 2. Site Investigation
Sequ
ence
of S
ite In
vesti
gatio
n
20
Sequ
ence
of S
ite In
vesti
gatio
n
Planning
Implementation
Reporting
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Why planning Depth of investigation Spacing of boreholes
21
Bore
hole
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Why planning?
• How many borings do we need?• How deep the borings should be?
The more the better, but what about the cost?
22
• Minimize cost of explorations and yet give reliable data.• Decide on quantity and quality depending on type, size and
importance of project and whether investigation is preliminary or detailed.
Planning for site investigation is required to:
• Decide on minimum depth and spacing of exploration.
Dep
th o
f Bor
ehol
eBorehole Spacing
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Why planning?
23
Dep
th o
f Bor
ehol
e
• In general, depth of investigation should be such that any/all strata that are likely to experience settlement or failure due to loading.
• The estimated depths can be changed during the drilling operation, depending on the subsoil encoun tered.
• To determine the approximate minimum depth of boring, engineers may use the following rules:
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Depth of investigation
24
1. Determine the net increase of stress, under a foundation with depth as shown in the Figure.
2. Estimate the variation of the vertical effective stress, ‘0 , with depth.
3. Determine the depth, D = D1, at which the stress increase ’ is equal to (1/10) q (q = estimated net stress on the foundation).
Determination of the minimum depth of boring
4. Determine the depth, D = D2, at which /'0 = 0.05.
5. Unless bedrock is encountered, the smaller of the two depths, D1 and D2, is the approximate minimum depth of boring required.
’0’
q
D
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Depth of investigation
25
Table shows the minimum depths of borings for buildings based on the preceding rule.
Depth of Boring
Number of StoriesBuilding width
(m)
What do you notice about this table?
CE 483 - Foundation Engineering - 2. Site Investigation
Planning
Depth of investigation
26
• There are no strict rules for the spacing of the boreholes. • The following table gives some general guidelines for borehole spacing. • These spacing can be increased or decreased, depending on the subsoil
condition. • If various soil strata are more or less uniform and predictable, the number of
boreholes can be reduced.
What do you notice about this table?
Type of project Spacing (m)
Planning
Spacing of boreholes
27
Planning
Implementation
Reporting
CE 483 - Foundation Engineering - 2. Site Investigation
Overview Boring Sampling Testing
Implementation
Sequ
ence
of S
ite In
vesti
gatio
n
28
Overview
Boring
Trial pits
Boreholes
Sampling
Soil Sampling
Rock Sampling
Testing
In-situ tests
Laboratory tests
The implementation phase of site investigation usually includes three important aspects:
CE 483 - Foundation Engineering - 2. Site Investigation
21 3
Implementation
29
Boring
Trial pits
Boreholes
Sampling
Soil Sampling
Rock Sampling
Testing
In-situ tests
Laboratory tests
CE 483 - Foundation Engineering - 2. Site Investigation
21 3
BoringImplementation
30
Trial pits
CE 483 - Foundation Engineering - 2. Site Investigation
• Trial pits are shallow excavations - less than 6m deep.
• The trial pit is used extensively at the surface for block sampling and detection of services prior to borehole excavation.
• For safety ALL pits below a depth of 1.2m must be supported.
BackhoePick and shovel
Depth Excavation Method
0-2m By Hand
2-4m Wheeled Back Hoe
4-6m Hydraulic Excavator
Trial Pit6m > depth
BoringImplementation
31
Boreholes
CE 483 - Foundation Engineering - 2. Site Investigation
1. Auger Boring2. Wash Boring 3. Rotary Drilling4. Percussion Drilling
Borehole• The right choice of method depends on:
– Ground condition: presence of hard clay, gravel, rock.
– Ground-water condition: presence of high ground-water table (GWT).
– Depth of investigation– Site access
• Boreholes may be excavated by one of these methods:
BoringImplementation
32
• This is the simplest of the methods. Hand operated or power driven augers may be used.• Suitable in all soils above GWT but only in
cohesive soil below GWT.
Hand operated augers
Power driven augers
Post hole auger Helical auger
1. Auger Boring
Boreholes BoringImplementation
33
• A casing is driven with a drop hammer. A hollow drill rod with chopping bit is inserted inside the casing.• Soil is loosened and removed from the
borehole using water or a drilling mud jetted under pressure.• Wash boring is a very convenient
method for soil exploration below the ground water table provided the soil is either sand, silt or clay. The method is not suitable if the soil is mixed with gravel or boulders.
2. Wash Boring
CE 483 - Foundation Engineering - 2. Site Investigation
Boreholes BoringImplementation
34
• In this method a heavy drilling bit is alternatively raised and dropped in such a manner that it powders the underlying materials which form a slurry with water and are removed as the boring advances.
• Possibly this is the only method for drilling in river deposits mixed with hard boulders of the quartzitic type.
3. Percussion Drilling
CE 483 - Foundation Engineering - 2. Site Investigation
Boreholes BoringImplementation
35
• In this method a rapidly retaining drilling bit (attached to a drilling rod) cut the soil and advance the borehole.
4. Rotary Drilling
• When soil sample is needed the drilling rod is raised and the drilling bit is replaced by a sampler.
• This method is suitable for soil and rock.
Drilling bit
Drilling rod
Rotary Head
Movement transmitter
CE 483 - Foundation Engineering - 2. Site Investigation
Boreholes BoringImplementation
36
Boring
Trial pits
Boreholes
Sampling
Soil Sampling
Rock Sampling
Testing
In-situ tests
Laboratory tests
CE 483 - Foundation Engineering - 2. Site Investigation
21 3
SamplingImplementation
37
Soil sampling
Soil samples are recovered carefully, stored properly to prevent any change in physical properties, and transferred to laboratory for testing.
CE 483 - Foundation Engineering - 2. Site Investigation
SamplingImplementation
Samples from each type of soils are required for laboratory testing to determine the engineering properties of these soils.
• Soil Sampling equipment?• Disturbed vs Undisturbed?
38
Soil Sampling equipment
There is a wide range of sampling methods such as Split-spoon, Thin-walled Tube. The choice of method depends on:
• the requirement of disturbed or undisturbed samples• Type of soil discovered at site (Gravel, Sand, Silt, Clay)
Split-spoon Sampler
Soil sampling SamplingImplementation
Soil Sample
advancement
39
Soil sampling SamplingImplementation
Soil Sampling equipment
40
• Two types of soil samples can be obtained during sampling: disturbed and undisturbed.
• The most important engineering properties required for foundation design are strength, compressibility, and permeability. These tests require undisturbed samples.
• Disturbed samples can be used for determining other properties such as Moisture content, Classification & Grain size analysis, Specific Gravity, and Plasticity Limits.
CE 483 - Foundation Engineering - 2. Site Investigation
Soil sampling SamplingImplementation
Disturbed vs Undisturbed
41
• It is nearly impossible to obtain a truly undisturbed sample of soil.
• The quality of an "undisturbed" sample varies widely between soil laboratories. So how is disturbance evaluated?
• Quality of samples is evaluated by calculating Area Ration AR:
Sampling tube
soil
The thicker the wall of the sampling tube, the greater the disturbance.
Outer Diameter
Inner Dia.
Good quality samples AR<10% .
CE 483 - Foundation Engineering - 2. Site Investigation
Soil sampling SamplingImplementation
Disturbed vs Undisturbed
42
Area Ration AR = ----------------- =
• Samples collected in Split-spoon Sampler is usually classified as “disturbed”.
What is the Area Ration?
CE 483 - Foundation Engineering - 2. Site Investigation
Soil sampling SamplingImplementation
Disturbed vs Undisturbed
43
• Core drilling equipment?• Core recovery parameters?
Rock samples are called “rock cores”, and they are necessary if the soundness of the rock is to be established.
CE 483 - Foundation Engineering - 2. Site Investigation
SamplingImplementation
Rock Sampling (Coring)
44
• Coring is done with either tungsten carbide or diamond core bits.• Rock sampler is called “core
barrel” which usually has a single tube.• Double or triple tube core
barrel is used when sampling of weathered or fractured rock.
Core barrel: (a) Single-tube; (b) double-tube
(a) (b)
Inner barrelOuter barrel
Core barrel
Rock
Rock
Rock
Corin
g bi
t
Drill rod
Diamond Drill Bit
Rock core
Rock
Rock Sampling (Coring) SamplingImplementation
Core drilling equipment
45
• Cores tend to break up inside the drill barrel, especially if the rock is soft or fissured. • Core recovery parameters are used to describe
the quality of core.• Length of pieces of core are used to determine:
– Core Recovery Ratio (Rr)– Rock Quality Designation (RQD)
Rock cores
CE 483 - Foundation Engineering - 2. Site Investigation
SamplingImplementation
Rock Sampling (Coring)
Core drilling equipment
46
10
• Assuming the following pieces for a given core run:
S L i=L
100%
(Core run)
Rr
( L i ≥ 10 cm )(Core run)
Recovery Ratio, Rr
Rock Quality Designation, RQD
Rock Sampling (Coring) SamplingImplementation
Core drilling equipment
Core recovery (lengths of intact pieces of core)
47
• So Rock Quality Designation (RQD) is the percentage of rock cores that have length ≥ 10 cm over the total drill length (core run).
• RQD may indicate the degree of jointing or fracture in a rock mass. e.g. High-quality rock has an RQD of more than 75%.
• RQD is used in rock mass classification systems and usually used in estimating support of rock tunnels.
Core recovery parameters
CE 483 - Foundation Engineering - 2. Site Investigation
Rock Sampling (Coring) SamplingImplementation
48
Class Example
Work out Rr and RQD for the following core recovery (intact pieces), assuming the core run (advance) is 150 cm.
What is the rock mass quality based on RQD?
CE 483 - Foundation Engineering - 2. Site Investigation
Rock Sampling (Coring) SamplingImplementation
Core recovery parameters
49
• Total core recovery L = 125 cm• Core recovery ratio:
Rr = 125/150 = 83%• On modified basis (for pieces ≥ 10cm),
95 cm are counted, thus: RQD = 95/150 = 63 %
• RQD = 50% - 75% Rock mass quality is “Fair”
Solution:
CE 483 - Foundation Engineering - 2. Site Investigation
Rock Sampling (Coring) SamplingImplementation
Core recovery parameters
?
? = ? S L i
L100% = S L i
L
50
Boring
Trial pits
Boreholes
Sampling
Soil Sampling
Rock Sampling
Testing
In-situ tests
Laboratory tests
CE 483 - Foundation Engineering - 2. Site Investigation
21 3
TestingImplementation
51
In-situ tests• Introduction• Groundwater measurements• Standard Penetration Test (SPT)• Cone Penetration Test (CPT)
TestingImplementation
• Plate Load Test (PLT)• Pressure-meter Test (PMT)• Flat Dilatometer Test (DMT)• Vane shear test (VST)
PLT
In Borehole
Piez
omet
er
52
Introduction
Definition: • In-situ tests are carried out in the field with intrusive testing equipment. • If non-intrusive method is required, then it is better to use geophysical
methods which use geophysical waves – i.e. without excavating the ground.
Advantage of in-situ testing (against lab testing)• It avoids the problems of sample recovery and disturbance • some in-situ tests are easier to conduct than lab tests • In-situ tests can offer more detailed site coverage than lab testing.
Testing standards• American Society for Testing and Materials (ASTM)• British Standard (BS)
CE 483 - Foundation Engineering - 2. Site Investigation
: In-situ tests TestingImplementation
53
Groundwater measurements
Why Groundwater:• Groundwater conditions are fundamental
factors in almost all geotechnical analyses and design studies.
Types of Groundwater measurements:• Determination of groundwater levels (GWT) and
pressures. Borehole instrumented with Piezometer is used for this purpose.• Measurement of the permeability of the
subsurface materials, particularly if seepage analysis is required. The test called Pumping test.
Piezometer
CE 483 - Foundation Engineering - 2. Site Investigation
: In-situ tests TestingImplementation
Ground water level
Standpipe
54
Standard Penetration Test (SPT)
• This empirical test consists of driving a split-spoon sampler, with an outside diameter of 50 mm, into the soil at the base of a borehole.
• Drivage is accomplished by a trip hammer, weighing 65 kg, falling freely through a distance of 760 mm onto the drive head, which is fitted at the top of the rods.
• The split-spoon is driven three times for a distance of 152.4 mm (6 in) into the soil at the bottom of the borehole. The number of blows required to drive (only) the last two 152.4 mm are recorded. The blow count is referred to as the SPT-N.
760 mm
152.4 mm (6 in) x 3 timesThe first one does not count
Falling Hammer
Definition
Drive head
Slit spoon
CE 483 - Foundation Engineering - 2. Site Investigation
: In-situ tests TestingImplementation
55
• Relatively quick, simple, reasonably cheap, and suitable for most soils.• good correlation between SPT-N and soil properties.• provides a representative soil sample for further
testing.
Disadvantage• SPT does not typically provide continuous data• Limited applicability to soil containing cobbles and
boulders.• Samples obtained from the SPT are disturbed.• SPT N blow require correction
Advantage
CE 483 - Foundation Engineering - 2. Site Investigation
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
56
• Corrections are normally applied to the SPT blow count (N) to account for:– Energy loss: during the test (about only 60% of energy remains)– Equipment differences: hammer, sampler, borehole diameter, rod
Corrections for energy and equipment
• The following equation is used to compensate for these factors:
(0.75-1.0)
(1.0-1.15)
(usually 0.50-0.80)
(0.8-1.0)
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Usually this correction is made by the Site Investigation operator.
60%
57
Corrections for overburden pressure
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
CN = overburden pressure correction factor
• In granular soil (sand, gravel) the SPT blows are influenced by the effective overburden pressure at the test depth:
Many equations have been suggested for CN – see Page 86, (Das’s text book). For example:
58
Standard Penetration Test (SPT)
Correlation between N and friction angle
• There are many equations suggested. The figure shows the correlation with the angle of shearing resistance of sand (according to Pecks, 1974).
TestingImplementation : In-situ tests
Angle of shearing resistance f’ (degree)
Cor
rect
ed S
PT N
blo
w
59
The following are the recorded numbers of SPT blows required for spoon penetration of three 152.4cm (6 in) in a sand deposit:
Class example
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Depth from ground surface (m) 1.5 3 4.5 6 7.5
SPT blows (blow/ 6 in) 3, 4, 5 7, 9, 10 7, 12, 11 8, 13, 14 10, 14, 15
The ground water table (GWT) is located at a depth of 4.5m. The wet unit weight of sand above GWT is 18 kN/m3, and the saturated unit weight of sand below GWT is 19.81 kN/m3.
• Draw a sketch of the foundation showing the given details of the soil.• Determine the standard penetration number (SPT-N) at each depth.• What is the corrected (SPT-N) value? (use Seed’s equation).• Determine the friction angle at depth 4m below the footing. (Use Peck’s
Equation or Chart).
Note. Assume the above SPT blows are corrected for energy and equipment.
Z, m SPT blow N60 s0’ (kPa) CN N f’
1.5 3, 4, 5 4+5=9 1.5x18 =27 0.27 1.7 15.3 35o
3 7, 9, 10 9+10=19 54 0.54
4.5 7, 12, 11 23
6 8, 13, 14 ?
7.5 10, 14, 15
60
Only the last 2 sets of blows count
Solution
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
g =18 kN/m3
gsat=19.8 kN/m3
2
4
Z
Corrected
61
• The corrected SPT N blow can be approximately correlated to many important engineering properties of soil such as shear strength & compressibility. • This equation shows the correlation with untrained shear strength Su (or Cu)
of clay. (also with OCR = Over Consolidation Ratio).
CE 483 - Foundation Engineering - 2. Site Investigation
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Correlation between N and untrained shear strength
In C
lay
62
• The table shows the correlation corrected SPT-N with untrained shear strength Su (or Cu) of clay (according to Terzaghi et al. 1996)
CE 483 - Foundation Engineering - 2. Site Investigation
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Correlation between N and untrained shear strength
63CE 483 - Foundation Engineering - 2. Site Investigation
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Class Example
shown belowthe Figure
64
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Solution
Z, m N60 s0’ (kPa) Cu (kPa) s0’ (MPa) OCR
3 51.5x16.5+
1.5x(19-9.81) = 38.5100x0.29
x50.72 =92.338.5/1000=
0.03850.193x(5/
0.038)0.689 = 5.5
4.5 838.5+1.5x(16.5-
9.81) = 48.5 129.6 0.0485
6 8
7.5 9
9 10
OCRav = Cu -av =
65
Standard Penetration Test (SPT)
Correlation between N and Relative Density Dr
• correlation between N60 and Relative Density of Granular Soil
TestingImplementation : In-situ tests
CE 483 - Foundation Engineering - 2. Site Investigation
Copy
righ
t res
erve
d to
Dr O
. Ham
za
For Clean sand onlyGeneral
66
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
CE 483 - Foundation Engineering - 2. Site Investigation
Very loose
Loose
Medium
Dense
Correlation between N and Relative Density Dr
67
Standard Penetration Test (SPT) TestingImplementation : In-situ tests
Correlation between Modulus of Elasticity and Standard Penetration Number
• The modulus of elasticity of granular soils (Es) is important parameter in estimation the elastic settlement of foundation.
• An approximate estimation for Es was given by Kulhawy and Mayne (1990) as:
68
Cone Penetration Test (CPT)
• called also "Dutch cone test“ or “Static Penetration test”.• The test method consists of pushing an
instrumented cone, with the tip facing down, into the ground at a slow controlled rate.• Cone: 60 degree apex cone, Dia = 36 mm.
Definition
Cone
CE 483 - Foundation Engineering - 2. Site Investigation
TestingImplementation : In-situ tests
Measures
• Cone or Tip resistance (qc) or (qt)
• Sleeve friction (fs)
• Water Pore pressure (ub)
Friction Ratio, Fr = qc
fs
qc or qt
fs
Hydraulic push at rate 20 mm/s
Cone Rod (36 mm dia.)
• Other variables e.g. Shear wave velocity (vs)
69
Cone Penetration Test (CPT)
CE 483 - Foundation Engineering - 2. Site Investigation
TestingImplementation : In-situ tests
• Soil profile (stratigraphy): soil type identification• Estimation of geotechnical
parameters (strength, compressibility, permeability)• Evaluation of groundwater
conditions (pore pressure)• Geo-environmental:
distribution and composition of contaminants
Applications:
Sample data
Sleev
e fric
tion, f s
Tip re
sista
nce, q
c
Pore
Pressu
re, u
Clay
Clay
& S
iltSi
lty C
lay
Clay & Sand
Fricti
on Ratio , F
r
70
Cone Penetration Test (CPT)
TestingImplementation : In-situ tests
– High in granular soil– Low in cohesive soil
– Low in granular soil– High in cohesive soil
• Friction Ratio Fr
• Point resistance qc
Soil Identification:
• However, the cone/tip (qc) and sleeve (fs) resistance increase with increasing overburden stress s0
• for accurate identification, normalization of qc & fs by overburden stress is required. Classification Chart (Robertson et al., 1983)
71
Cone Penetration Test (CPT)
CE 483 - Foundation Engineering - 2. Site Investigation
TestingImplementation : In-situ tests
• Inability to penetrate through gravels and cobbles• Newer technology = less populated database
than SPT• Lack of sampling
Disadvantages:
• Borehole is not necessary• Almost continuous data (reading every 10mm)• Elimination of operator error (automated)• Reliable, repeatable test results
Advantages:
72
Cone Penetration Test (CPT)
CE 483 - Foundation Engineering - 2. Site Investigation
TestingImplementation : In-situ tests
• In Sand: the drained friction angle
Correlation with shear strength
where: qc = the cone (tip) (point) resistance
s’0 & s0 = effective and total overburden pressure, respectively
NK = Bearing factor depends on type of cone (varies from 11-20)OCR = Over Consolidation Ratio
• In Clay: undrained shear strength cu
(Ricceri et all’s. 2002)
73
Cone Penetration Test (CPT)
TestingImplementation : In-situ tests
Class example: Correlation with shear strength
Use equation proposed by Ricceri et all’s. 2002.
74
Cone Penetration Test (CPT)
TestingImplementation : In-situ tests
Solution:
Depth, m qc (MPa) s0’ (kPa) qc /s0’ f’ (Rad) f’ (deg)
1.5 2.06 1.5 x 16 =24 2060 / 24 = 85.8 0.690.69x180/
p=40o
3 4.23 48 88.1
4.5 6.01
6 8.18
7.5 9.97
9.0 12.42f’av =
f’av = Sf’ / 6Note. tan -1 is inverse tangent, the angle returned is in Radian.
75
Plate Load Test (PLT) TestingImplementation : In-situ tests
• The test essentially consists in loading a rigid steel plate at the foundation level and determining the settlement corresponding to each load increments.
• The ultimate bearing capacity is then taken as the load at which the plate starts sinking at a rapid rate.
• Plate load test is a field test to determine the ultimate bearing capacity of soil.
76
Laboratory tests
CE 483 - Foundation Engineering - 2. Site Investigation
TestingImplementation
77
• Basic physical properties tests (Moisture content, Specific gravity, Soil Indexes, ..)
• Particle size test (sieving, Sedimentation)• Direct shear box test• Unconfined compression test• Triaxial test• Consolidation test• Permeability test• Other lab tests: Chemical test (pH,
contamination,..)
CE 483 - Foundation Engineering - 2. Site Investigation
Laboratory tests
TestingImplementation
78
Planning
Implementation
Reporting
CE 483 - Foundation Engineering - 2. Site Investigation
Preparation of Borehole Site Investigation Report
Reporting
Sequ
ence
of S
ite In
vesti
gatio
n
79CE 483 - Foundation Engineering - 2. Site Investigation
Reporting
Preparation of Boring Logs
Initial information: Name and address of the drilling company, Driller’s name, Job description and reference number, boring information (number, type, and location of, and date of boring).
Example of a typical boring log
80CE 483 - Foundation Engineering - 2. Site Investigation
Subsurface stratification: which can be obtained by visual observation of the soil brought out by auger, split-spoon sampler, and thin-walled Shelby tube sampler.
Groundwater: Elevation of water table and date observed, use of casing and mud losses, and so on
Reporting
Preparation of Boring Logs
81CE 483 - Foundation Engineering - 2. Site Investigation
In-situ tests: Standard penetration resistance and the depth of SPT
Samples: Number, type, and depth of soil sample collected; in case of rock coring, type of core barrel used and, for each run, the actual length of coring, length of core recovery, and RQD.
Reporting
Preparation of Boring Logs
82
The following borehole is part of a site investigation (SI) carried out over a proposed location of a bridge.
Assess the subsoil conditions and ground-water conditions based on the borehole data. In particular write about:
• Soil layers: types, description, depth…• Soil properties: shear strength properties -based on SPT.• Ground water depth
Reporting
Preparation of Boring Logs
Class example
Copy
righ
t res
erve
d to
Dr O
. Ham
za
83CE 483 - Foundation Engineering - 2. Site Investigation
84CE 483 - Foundation Engineering - 2. Site Investigation
• When: After the completion of all of the field and laboratory work, a site investigation report is prepared.
• Why: for the use of the design office and for reference during future construction work.
• The report is also called soil exploration report or Geotechnical Factual report.
SITE
INVESTIGATION
Reporting
Site Investigation Report
What should be included in the site investigation report?
85CE 483 - Foundation Engineering - 2. Site Investigation
The report should contain descriptions of the followings:
• Purpose & Scope of the investigation• Site & Structure: site location, existing structures, drainage conditions,
vegetation,… and information about the structure.• Factual Details of field exploration: boreholes, samples, and testing.
For each type, quantities, method, tools should be presented.• Geological setting of the site (variation of depth and thickness of layers
as interpreted from the borings)• Subsoil and water-table conditions, (soil parameters as interpreted
from the testing results).• Design analysis & recommendations: type of foundation, allowable
bearing pressure, settlement estimation, and any special construction procedure; alternatives design solution. • Conclusions and limitations of the investigations
Reporting
Site Investigation Report
Usu
ally
giv
en in
ano
ther
repo
rt(G
eote
chni
cal D
esig
n Re
port
)
86CE 483 - Foundation Engineering - 2. Site Investigation
The following graphical presentations must be attached to the report:
1. General map showing site location 2. A plan view of the location of the borings with
respect to the proposed structures and those nearby
3. Boring logs (including in-situ tests results and samples)
4. Laboratory test results
5. Other graphical presentations (geotechnical cross section based on the boring logs, photos of the field work and soil samples,…)
Reporting
Site Investigation Report
87
Geotechnical cross section based on the boring logs
Reporting
Site Investigation Report