TOPICS & SYLLABUS:

I. Introduction and Geotechnical

Topic 1: Site Investigation Properties of Soil
Topic 2: Slope Stability II. Natural Soil Deposits and Subsoil
Exploration
Topic 3: Shallow Foundations
Topic 4: Mat (Raft) Foundations
Topic 5: Pile Foundations
Topic 6: Earth Retaining Structures

1
Civil Engineering 2022/2023
Subject: Geotechnical Design (CSE40403)

Site investigation
Part II- Natural Soil Deposits and Subsoil
Exploration
By Dr. Ning Zhang
Office: ZS928, Tel: 3400-8473
Email: ning-cee.zhang@polyu.edu.hk
Consultation hours: 15:00~17:00 Monday
2
About me

Personal website
https://www.polyu.edu.hk/cee/people/academic-staff/dr-zhang-ning/
https://sdyszn.wixsite.com/ningzhang

➢ Education

• Ph.D, Shanghai Jiao Tong University, Shanghai, China 9/2013 – 12/2019

• B.Eng., Southeast University, Nanjing, China 9/2009 – 6/2013
About my research
• Smart Shield tunneling
• Artificial intelligence
• Data-driven constitutive modeling

Ground
collapse

Damage to buildings and pipelines

Imbalanced
Earth
pressure

Expanding deep learning model

Expanding database

Data from constructed tunnels Data from constructing tunnels

prediction

Constructed Tunnel New constructing Next Tunnel

segments Tunnel segments segments

Excavation face
Main content:

I. Natural Soil Deposits

❖ Soil Origin
❖ Transported Soils
❖ Residual Soils
❖ Peats and Organic Soils

II. Subsurface Exploration

❖ Subsurface Exploration Program
❖ Boring and Sampling
❖ Field Mechanical Testing
❖ Geophysical Exploration

5
I. Natural Soil Deposits Atmosphere:
Air, wind, rain/sunny

life Rocks
Minerals

Weathering
Hydrosphere

Soils
Transported soils
Residual soils
Peats/organic soils
6
I.1 Soil origin
Most of the soils that cover the ❖ Changes in temperature result in expansion
earth are formed by the weathering and contraction of rock due to gain and loss
of various rocks. of heat.
Two general types of weathering: ❖ Continuous expansion and contraction will
result in the development of cracks in rocks.
(1) Physical weathering, is a process ⼩薄⽚
by which rocks are broken down ❖ Flakes and large fragments of rocks are split.
into smaller and smaller pieces by
❖ Frost action is another source of physical
physical forces without any change
weathering of rocks.
in the chemical composition.
❖ Water can enter the pores, cracks, and other
(2) Chemical weathering, is a
openings in the rock. Continuous freezing
process of decomposition or 溶化
and thawing will result in the breakup of a
mineral alteration in which the
rock mass.
original minerals are changed into
表⽪削落
something entirely different. ❖ Exfoliation by which rock plates are peeled
off from large rocks by physical forces.
❖ Action of running water, glaciers, wind,
ocean waves, etc.
7
I.1 Soil origin
Most of the soils that cover the
earth are formed by the weathering
of various rocks.
Two general types of weathering:
(1) Physical weathering, is a process
by which rocks are broken down
into smaller and smaller pieces by
physical forces without any change
in the chemical composition.
(2) Chemical weathering, is a
process of decomposition or
mineral alteration in which the
Common minerals in igneous rocks are quartz,
original minerals are changed into
feldspars, and ferromagnesian minerals. The
something entirely different.
decomposed products of these minerals due to
chemical weathering listed in the above Table.

8
I.1 Soil origin

Most rock weathering is a combination of physical and chemical weathering.

❖ Soil produced by the weathering of rocks can be transported by physical processes
to other places. The resulting soil deposits are called transported soils.
❖ In contrast, some soils stay where they were formed and cover the rock surface
from which they derive. These soils are referred to as residual soils.
❖ There are peats and organic soils, which derive from the decomposition of organic
materials (plant and animal detritus).

9
I.2 Transported soils
(1) Gravity transported soil
Most rock weathering is a combination of (2) Lacustrine (lake) deposits
physical and chemical weathering. (3) Alluvial or fluvial soil deposited
by running water
❖ Soil produced by the weathering of rocks
can be transported by physical processes (4) Glacial deposited by glaciers
to other places. The resulting soil deposits (5) Aeolian deposited by the wind
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.

10
 I.2 Transported soils

Landslides in HK
after a rainstorm

Summary for the

locations of landslides
in HK (1982-2004 )

11
I.2 Transported soils
(1) Gravity transported soil
Most rock weathering is a combination of (2) Lacustrine (lake) deposits
physical and chemical weathering. (3) Alluvial or fluvial soil deposited
by running water
❖ Soil produced by the weathering of rocks
can be transported by physical processes (4) Glacial deposited by glaciers
to other places. The resulting soil deposits (5) Aeolian deposited by the wind
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.

12
I.2 Transported soils
(1) Gravity transported soil
Most rock weathering is a combination of (2) Lacustrine (lake) deposits
冲积的
physical and chemical weathering. (3) Alluvial or fluvial soil deposited
by running water
❖ Soil produced by the weathering of rocks
can be transported by physical processes (4) Glacial deposited by glaciers
to other places. The resulting soil deposits (5) Aeolian deposited by the wind
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.

13
 I.2 Transported soils
辫状河流
Cross section of a braided-stream deposit

Fine sand

Gravel

Silt

Coarse sand

Levee and backswamp deposit

Formation of point bar deposits and

oxbow lake in a meandering stream

14
I.2 Transported soils
(1) Gravity transported soil
Most rock weathering is a combination of (2) Lacustrine (lake) deposits
physical and chemical weathering. (3) Alluvial or fluvial soil deposited
by running water
❖ Soil produced by the weathering of rocks
can be transported by physical processes (4) Glacial deposited by glaciers
to other places. The resulting soil deposits (5) Aeolian deposited by the wind
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.

15
I.2 Transported soils
(1) Gravity transported soil
Most rock weathering is a combination of (2) Lacustrine (lake) deposits
physical and chemical weathering. (3) Alluvial or fluvial soil deposited
by running water
❖ Soil produced by the weathering of rocks
can be transported by physical processes (4) Glacial deposited by glaciers
to other places. The resulting soil deposits (5) Aeolian deposited by the wind
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.
(e.g. in desert)

16
I.3 Residual soils

Most rock weathering is a combination of

physical and chemical weathering.
❖ Soil produced by the weathering of rocks
can be transported by physical processes
to other places. The resulting soil deposits
are called transported soils.
❖ In contrast, some soils stay where they
were formed and cover the rock surface
from which they derive. These soils are
referred to as residual soils.
❖ There are peats and organic soils, which
derive from the decomposition of organic
materials.

17
I.4 Peats and organic soils

Most rock weathering is a combination of

physical and chemical weathering.
❖ Soil produced by the weathering of rocks
can be transported by physical processes
to other places. The resulting soil deposits
are called transported soils. Major characteristics:
❖ In contrast, some soils stay where they 1) Natural moisture content may
were formed and cover the rock surface range from 200 to 300 %.
from which they derive. These soils are 2) Highly compressible.
referred to as residual soils. 3) Under loads, a large amount of
❖ There are peats and organic soils, which settlement is derived from
derive from the decomposition of organic secondary consolidation.
materials (plant and animal detritus).

18
For exam
Rocks
Minerals

Atmosphere physical ✓ Gravity transported soil

(1)? ✓ (3)?Lake deposits
Biosphere Weathering ✓ Alluvial or fluvial soil deposited
Chemical by running water
(2)?
✓ Glacial deposited by glaciers
hydrosiphere
deposited
✓ (4)?byolian wind

Residual soils Transported soils

Below horizons
✓ Topsoil
Soils
✓ (5)? completdy weathered
Peats/organic soils
✓ Highly weathered
with plant and animal detritus
✓ Moderately weathered under wads , a large ✓
amount of settlement
High water content
✓ Slightly weathered
✓ (6)? is derived from 2nd ✓ (7)?highly compressible
freshrock consolidation ✓ (8)?
19
Main content:

I. Natural Soil Deposits

❖ Soil Origin
❖ Transported Soils
❖ Residual Soils
❖ Peats and Organic Soils

II. Subsurface Exploration

❖ Subsurface Exploration Program
❖ Boring and Sampling
❖ Field Mechanical Testing
❖ Geophysical Exploration

20
II.1 Subsurface exploration program

The purpose of subsurface exploration is to obtain information that will aid the
geotechnical engineer in
❖ Selecting the type and depth of foundation suitable for a given structure.
❖ Evaluating the load-bearing capacity of the foundation.
❖ Estimating the probable settlement of a structure.
❖ Determining potential foundation problems (e.g., expansive soil, collapsible soil,
sanitary landfill, etc.).
❖ Determining the location of the water table.
❖ Predicting the lateral earth pressure for structures such as retaining walls, sheet pile
bulkheads, and braced cuts.
❖ Establishing construction methods for changing subsoil conditions

21
 II.1 Subsurface exploration program
Subsurface exploration comprises several steps:
❖ Collection of Preliminary Information ✓ Information regarding the type of
勘测 structure to be built and its general use;
❖ Reconnaissance
✓ A general idea of the topography;
❖ Site Investigation ✓ Type of soil to be encountered near and
around the proposed site.

✓ More detailed topography of the site (ditches, debris, cracks, etc.);

✓ Type of vegetation at the site (relating to the nature of the soil);
桥基
✓ High-water marks (nearby buildings and bridge abutments);
✓ Groundwater levels by checking nearby wells;
✓ Existence of any cracks in walls or other problems nearby;
分层
✓ Stratification and physical properties of the soil nearby from any
available soil-exploration reports on existing structures.

22
(High-water mark: https://en.wikipedia.org/wiki/High_water_mark)
II.1 Subsurface exploration program
Subsurface exploration comprises several steps:
❖ Collection of Preliminary Information
❖ Reconnaissance
❖ Site Investigation

钻孔
✓ It consists of planning, making test boreholes, and collecting soil samples
at desired intervals for subsequent observation and laboratory tests.
✓ The approximate required minimum depth of the borings should be
predetermined.
✓ There are no hard-and-fast rules for borehole spacing. Spacing can be
increased or decreased, depending on the condition of the subsoil. If
various soil strata are more or less uniform and predictable, fewer
boreholes are needed than in nonhomogeneous soil strata.
23
 F
II.1 Subsurface exploration program q = F/(B*L)
Subsurface exploration comprises several steps:
❖ Collection of Preliminary Information
❖ Reconnaissance
❖ Site Investigation

(For a simple shallow foundation)

Rule of ASCE to determine the approximate minimum depth of boring
✓ Determine the net increase in the effective stress Ds’ under a foundation with depth.
✓ Estimate the variation of the initial vertical effective stress s’0 with depth.
✓ Determine the depth D1 at which Ds’= 0.1*q (q= net stress on the foundation).
✓ Determine the depth D2 at which Ds’/s’0 = 0.05.
✓ Choose the smaller of the two depths (D1 & D2), just determined as the approximate
minimum depth of boring required, unless bedrock is encountered. 24
II.1 Subsurface exploration program
Subsurface exploration comprises several steps:
❖ Collection of Preliminary Information
❖ Reconnaissance
❖ Site Investigation Depth of
boring Number of
Some empirical formulations and requirements: stories

(1) For light steel or narrow concrete buildings Db = 3S 0.7

(2) For heavy steel or wide concrete buildings Db = 6S 0.7
(3) When deep excavations are anticipated, the
depth of boring should be at least 1.5 times Approximate Spacing of Boreholes
the depth of excavation.
(4) The minimum depth of core boring into the
bedrock is about 3 m in the case of the
bedrock being considered as foundation.

25
Exercise

The purpose of subsurface exploration:

✓ Type and depth of foundation, load-bearing capacity, settlement;
✓ ???; potentialfoundation problems ,
water table

✓ ???; lateralearthpressure constreection method

,

Subsurface exploration comprises several steps:

✓ Collection of Preliminary Information
✓ ??? Reconnaissance
for subsequent observation and laboratory tests
✓ Site Investigation Boreholes (for what?)
✓ ??? minimumdepth of borings
✓ ??? borehole
spacing

26
 II.2 Boring and Sampling
Exploratory Borings in the Field
螺旋钻
❖ Auger boring is the simplest method of making exploratory boreholes.
❖ Two types of hand auger (< 3 to 5 m): the posthole auger and the helical auger.
❖ Electrical continuous-flight augers are probably the most common method used
for advancing a borehole (up to 60~70 m):
- Rotary drilling, for soils not too hard;
- Percussion drilling, for hard soil and rock.

Posthole Helical
auger auger

27
II.2 Boring and Sampling
Sampling of soils
Two types of soil samples during subsurface exploration: disturbed and undisturbed.

Disturbed samples can generally be used for:

❖ Grain-size analysis
❖ Determination of liquid and plastic limits
❖ Specific gravity of soil solids
❖ Determination of organic content

Undisturbed soil samples can be used for:

❖ Consolidation (oedometer) test
❖ Hydraulic conductivity (permeability) test
❖ Shear strength tests (direct, triaxial…)

28
II.2 Boring and Sampling
Sampling of soils

Four typical sampling methods:

(1) Split-Spoon Sampling
(2) Sampling with a Scraper Bucket
(3) Sampling with a Thin-Walled Tube
(4) Sampling with a Piston Sampler

29
II.2 Boring and Sampling Exercise
AR ?
[1] Split-Spoon Sampling
Split-spoon samplers can
be used in the field to
obtain soil samples that
are generally disturbed,
but still representative.

How to estimate the degree of disturbance for a soil sample?

AR = Area ratio (ratio of disturbed area to total area of soil)

D −D
2 2
AR ( % ) = o
2
i
100 Do = Outside (or outer) diameter of the sampling tube
Di Di = Inside (or inner) diameter of the sampling tube

When the area ratio is 10% or less, the sample

generally is considered to be undisturbed.
30
II.2 Boring and Sampling
[2] Sampling with a Scraper Bucket
卵⽯
When the soil deposits are sand mixed with pebbles, obtaining samples by split-spoon
with a spring core catcher may not be possible because the pebbles may prevent the
springs from closing. In such cases, a scraper bucket may be used to obtain disturbed
representative samples.

31
II.2 Boring and Sampling
[3] Sampling with a Thin-Walled Tube
❖ Thin-walled tubes are made of seamless steel and are frequently used to obtain
undisturbed clayey soils.
❖ The most common dimension: outside diameter of 50.8 mm or 76.2 mm.
❖ The bottom end of the tube is sharpened.

Sharpened end

Exercise
A thin-walled tube with 50.8 mm outside diameter has a wall thickness of 1.63 mm.
How is the degree of disturbance?

32
 II.2 Boring and Sampling
[4] Sampling with a Piston Sampler
When undisturbed soil samples are very soft
or larger than 76.2 mm in diameter, they tend
to fall out of the sampler. Piston samplers are
particularly useful under such conditions.
❖ Initially, the piston closes the end of the
tube. The sampler is lowered to the
bottom of the borehole, and the tube is
pushed into the soil hydraulically, past the
piston.
❖ Then the pressure is released through a
hole in the piston rod.
To a large extent, the presence of the piston
prevents distortion in the sample by not
letting the soil squeeze into the sampling
tube very fast and by not admitting excess
soil. Consequently, samples obtained in this
manner are less disturbed than those 33
obtained by Shelby tubes.
II.2 Boring and Sampling
⽔压计
Observation of Water Tables
❖ If water is encountered in a borehole during
a field exploration, that fact should be
recorded.
❖ In soils with high hydraulic conductivity (e.g.
in sand), the level of water in a borehole will
stabilize about 24 hours after completion of
the boring.
❖ In highly impermeable layers (e.g. in clay),
the water level in a borehole may not
stabilize for several weeks. A piezometer
should be used with periodic checking until
the water level stabilizes.

34
 Exercise
Exploratory Borings in the Field
hand
✓ ??? augers (< 3 to 5 m): the posthole auger and the helical auger.
electrical continuous flight
-

✓ ??? augers (up to 60~70 m): rotary drilling (soft), percussion drilling (hard)

Sampling of soils
physical
✓ Disturbed samples, used for tests of ??? properties
✓ Undisturbed samples, used for ??? properties
hydro -
mechanical

Four typical sampling methods

√ or not???
✓ Split-Spoon Sampling: for clayey soils, disturbed
√
✓ Sampling with a Scraper Bucket: for sand mixed with pebbles, disturbed or not???
✓ Sampling with a Thin-Walled Tube: for clayey soils, disturbed or not???
√
✓ Sampling with a Piston Sampler: for very soft clays or large-diameter tube, disturbed or
not???
√
Observation of Water Tables
24
✓ In sandy soils, directly measure the water level in ??? h after borehole completion
✓ In clayey soils, use piezometer to ??? check the water level 35
periodic
II.3 Field Mechanical Testing ✓ sample disturbance
Why need field mechanical testing? ✓ size effect
✓ boundary effect
Limitations of lab tests:
✓ expensive and time consuming

Typically, five field testing methods are used:

Blow Penetrate Expand Expand Rotate wading
method

SPT CPT DMT PMT VST

Pressurem-
Standard Cone Dilatometer eter Test Vane
Penetration Penetration Test Shear
Test Test Test
36
 https://en.wikipedia.org/wik
II.3 Field Mechanical Testing i/Standard_penetration_test

[1] Standard Penetration Test (SPT)

❖ During Split-Spoon Sampling, the sampler is driven
into the soil by hammer blows to the top of the drill
rod. The standard weight of the hammer is 622.72 N.
Becausethe soilisconsidered to be disturbed the
❖ The number of blows required for a spoonaction by
7

of boring
penetration of three 152.4 mm intervals are a nole
recorded. The number of blows required for the last
two intervals (why?) are added to give the standard
penetration number, N, at that depth.
Input energy = effective energy + energy dissipated Average energy ratio:
Actual hammer energy to the sampler Effective energy
Er ( % ) = 100
Input energy
❖ The N-value to a Er of 60%, noted as N60, is used for
correlating mechanical properties of soils.
N60 = standard penetration number
 H B S R N N = measured penetration number
N 60 = H = hammer efficiency (%)
60
B = correction for borehole diameter
622.72 N = 140 Pound S = sampler correction 37
152.4 mm = 6 inch R = correction for rod length
 II.3 Field Mechanical Testing H = hammer efficiency (%)
B = correction for borehole diameter
[1] Standard Penetration Test (SPT)  H B S R N S = sampler correction
N 60 =
60 R = correction for rod length

38
II.3 Field Mechanical Testing

Some correlations by N60

atmospheric pressure
(=101.325 kN/m2)
Undrained shear strength of clay cu = 0.29 N 600.72 pa

0.689
Overconsolidation ratio, OCR of clay  N 60 
OCR = 0.193  
s 
 0 
Effective vertical stress
Unconfined compression strength (UCS) of clay (in MPa)
consisteney index
 7
w −w 
 CI = L 
 wL − wp 
waterotent
」

of soil

39
II.3 Field Mechanical Testing Correction coefficient. For example,
Liao and Whitman’s relationship (1986)
Some correlations by N60
pa atmospheric
 = CN N 60 CN =
Correction for N60 in Granular Soil N 60 s 0
pressure
(101.325 kN/m2)
Effective vertical
stress
Relative Density of Granular Soil uniformity coefficient

(Kulhawy and Mayne 1990)

‘
(Meyerhof 1957)

‘
(Cubrinovski and Ishihara 1999)

40
II.3 Field Mechanical Testing Correction coefficient. For example,
Liao and Whitman’s relationship (1986)
Some correlations by N60
pa
 = CN N 60 CN =
Correction for N60 in Granular Soil N 60 s 0

Friction Angle of Granular Soil ‘ ‘

(Wolff 1989)
‘

(Kulhawy and Mayne 1990)

‘ (Hatanaka and Uchida 1996)

Elastic Modulus of Granular Soil

‘ (Kulhawy and Mayne 1990)

41
II.3 Field Mechanical Testing

Compactness and consistency of soil (GeoGuide 3, HK)

(Blows/300 mm penetration, not N60)

Approximate relation
between N and Dr of
soil (GeoGuide 3, HK)

42
 https://en.wikipedia.org/wiki/Shear_vane_test
II.3 Field Mechanical Testing
[2] Vane Shear Test (VST)
The VST is used during the drilling operation
to determine the in-situ undrained shear
strength of clay soils—particularly soft clays.
only
Testing procedure:
(1) The vanes of the apparatus are pushed
into the soil at the bottom of a borehole
without disturbing the soil appreciably.
(2) Torque is applied at the top of the rod to
rotate the vanes at a standard rate (0.1⁰/sec).
This rotation will induce failure in a soil of
cylindrical shape surrounding the vanes.
(3) The maximum torque, T, applied to cause
failure is measured. The undrained shear
strength is estimated by
T  D2 H  D 
cu = K=  1 +  (why?) 43
K 2  3H 
II.3 Field Mechanical Testing
T
[2] Vane Shear Test (VST)
T  D2 H  D  (why?)
cu = K=  1 + 
K 2  3H 
Three failure surfaces: side of cylinder, top and bottom

Part 1: side of cylinder D

T1 =  DHcu
2

Part 2: top and bottom

D 2

T2 = 2  2 r  dr  cu  r
0
dr
( D 2)
D 2 3
 D3
= 4 cu  r 2 dr = 4 cu = cu r
0
3 6
In total:
D  D3 T  D2 H  D 
T = T1 + T2 =  DHcu + cu  cu = with K =  1 + 
2 6 K 2  3H  44
 ⾃⼰算 PI = Wc -

Wp
II.3 Field Mechanical Testing
[2] Vane Shear Test (VST)
The cu is overestimated by VST. (Morris and Williams 1994)
In real design cu needs to be
corrected: cu = cu (VST) * VST=field

(Bjerrum 1972)

Preconsolidation pressure of clay

s c = 7.04 ( cu )
0.83

Overconsolidation ratio of clay cu

OCR = 
s 0
(Mayne and Mitchell 1988)

(Hansbo 1957)

(Larsson 1980) 45
 https://en.wikipedia.org/wiki/Cone_penetration_test
II.3 Field Mechanical Testing
[3] Cone Penetration Test (CPT)
❖ The test is also called the static penetration test,
and no boreholes are necessary to perform it.
❖ In the original version, a cone with a base area of
10 cm2 was pushed into the ground at a steady rate
(20 mm/sec). Friction
load cell
❖ Two measures by the CPT can be obtained:
(a) the cone resistance (qc) to penetration developed
by the cone, which is equal to the vertical force
applied to the cone, divided by its horizontally
projected area;
(b) the frictional resistance (fc) which is equal to the
vertical force applied to the sleeve, divided by its
surface area—actually, the sum of friction and
adhesion.

Cone
46
load cell
47
 II.3 Field Mechanical Testing
[3] Cone Penetration Test (CPT)
Friction ratio (Fr) is defined as

Frictional resistance f c
Fr = =
Cone resistance qc

Empirical formulations by
Anagnostopoulos et al. (2003):

mean particle
diameter of the soil
Typical results of CPT
Attention: not always applicable! 48
II.3 Field Mechanical Testing
[3] Cone Penetration Test (CPT)
(Kulhawy and Mayne 1990)
Relative density of sand

49
II.3 Field Mechanical Testing
[3] Cone Penetration Test (CPT)

Drained Friction Angle of sand

(Kulhawy and Mayne 1990)

(Ricceri et al. (2002)

(Lee et al. 2004)

horizontal effective stress

50
II.3 Field Mechanical Testing
Attention: total vertical stress, not effective
[3] Cone Penetration Test (CPT)
(Robertson and Campanella 1983)
Undrained Shear Strength

Preconsolidation pressure

Overconsolidation ratio

51
II.3 Field Mechanical Testing
[3] Cone Penetration Test (CPT) (Anagnostopoulos et al. 2003)
Correlation between qc and N60

52
 https://en.wikipedia.org/wiki/Pressuremeter_test
II.3 Field Mechanical Testing
[4] Pressuremeter Test (PMT)
❖ The PMT is an in-situ test conducted in a borehole. It
was originally developed by Menard (1956) to measure
the strength and deformability of soil.
❖ The PMT consists of a probe with three cells (top and
bottom guard cells, the middle measuring cell).
❖ The common dimension of probe has a diameter of 58
mm and a length of 420 mm.
❖ The probe cells can be expanded by liquid/gas. The
guard cells are expanded to reduce the end-condition
effect on the measuring cell (V0 = 535 cm3).
❖ During the expansion, the soil around the borehole is
first pushed back into the initial state (with an
incremental volume v0), and then continues to expand.
❖ The soil is considered to have failed when the total
volume of the expanded cavity is about twice the
volume of the original cavity (V = 2*(V0 + v0)). 53
II.3 Field Mechanical Testing
[4] Pressuremeter Test (PMT)
Zone I represents the reloading
portion during which the soil
around the borehole is pushed back
into the initial state (i.e., the state it
was in before drilling). The pressure
p0 represents the in-situ total
horizontal stress.
Zone II represents a pseudoelastic
zone in which the cell volume
versus cell pressure is practically
linear (with a pressuremeter
modulus Ep). The pressure pf
represents the yield pressure.
Zone III is the plastic zone. The
pressure pl represents the limit
pressure.

54
II.3 Field Mechanical Testing
[4] Pressuremeter Test (PMT)

Pressuremeter modulus
shear modulus

 Dp 
>

G = (Vo + vm )  
 Dv 
E p = 2 (1 + m s ) G ms = Poisson’s ratio (~ 0.33)

Preconsolidation pressure
(Kulhawy and Mayne 1990) s c = 0.45 pl

Undrained shear strength of clay pl − p0

cu =
(Baguelin et al. 1978) Np
 Ep 
N p = 1 + ln  
3c
 u
Coefficient of in-situ Pore water pressure
p −u
earth pressure at rest K0 = 0 0 55
s 0 In-situ vertical effective stress
Appendix: Cavity expansion analysis for PMT

56
 Exercise

Field testing methods Measures For clayey soils For sandy soils Applied by

Standard Penetration Test (SPT) N60 Ca ,OCR , UESRr ,

P ,
Es Blow

Cu Cu 6d
'

OCR NA Rotate
Vane Shear Test (VST) , . .
.

Cone Penetration Test (CPT) Ee , f:

Ca ,
6c .
ocR 2r p , Penetrate
Pressuremeter Test (PMT) Po ,
Pf ,
P,oVCa, 6 'd ,
Ko . Lp Ko , EP Expand
Dilatometer Test (DMT)
http://geoinvention.com/teaching_site.html

59
II.4 Geophysical Exploration
Three typical geophysical exploration techniques:
✓ Seismic refraction survey
✓ Cross-hole seismic survey
✓ Resistivity survey
Advantages: rapid evaluation, large areas, less expensive than field testing.
Drawbacks: definitive interpretation is difficult, thus only for preliminary work.
(problem of accuracy)

60
II. Subsoil Exploration Report
General requirements of a Report:
1) A description of the scope of the investigation
2) A description of the proposed structure for which the subsoil exploration has been
conducted
3) A description of the location of the site, including any structures nearby, drainage
conditions, the nature of vegetation on the site and surrounding it, and any other
features unique to the site
4) A description of the geological setting of the site
5) Details of the field exploration—that is, number of borings, depths of borings, types of
borings involved, etc.
6) A general description of the subsoil conditions, as determined from soil specimens and
from related laboratory tests, standard penetration resistance and cone penetration
resistance, etc.
7) A description of the water-table conditions
8) Recommendations regarding the foundation, including the type of foundation
recommended, the allowable bearing pressure, and any special construction procedure
that may be needed; alternative foundation design procedures should also be
discussed in this portion of the report
67
9) Conclusions and limitations of the investigations
II. Subsoil Exploration Report
Necessary attachments to the report:
1) A site location map
2) A plan view of the location of the borings with
respect to the proposed structures and those
nearby
3) Boring logs
4) Laboratory test results
5) Other special graphical presentations

68