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GEOTECHNICAL CHARACTERIZATION
THROUGH PRESSUREMETER AND
LABORATORY TESTING FOR ALLUVIAL SOILS
Year: 2014
ZUBAIR MASOUD
2006-PhD-CIVIL-06
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF ENGINEERING AND TECHNOLOGY
LAHORE, PAKISTAN
GEOTECHNICAL CHARACTERIZATION THROUGH
PRESSUREMETER AND LABORATORY TESTING FOR
ALLUVIAL SOILS
Year: 2014
ZUBAIR MASOUD
2006-PhD-CIVIL-06
INTERNAL EXAMINER EXTERNAL EXAMINER
Prof. Dr. Aziz Akbar Dr. Tahir Masood
CHAIRMAN DEAN
Civil Engineering Department Faculty of Civil Engineering
Thesis submitted in partial fulfillment of the requirements for the Degree of Doctor of
Philosophy in Civil Engineering
DEPARTMENT OF CIVIL ENGINEERING
UNIVERSITY OF ENGINEERING AND TECHNOLOGY
LAHORE, PAKISTAN
i
Dedicated to
My Parents
ii
ACKNOWLEDGEMENTS
I would like to express my heartiest gratitude to Professor Dr. Aziz Akbar, who
supervised this research. His precious knowledge and vast experience in this research area
made this research successful. The support and encouragement he provided made the
years of research with him memorable.
My heartiest thanks are due to Prof. Dr. A.S. Shakir, Prof. Dr. Muhammad Ilyas for their
guidance and suggestions.
Special thanks are due to Professor Dr. Khalid Farooq, Associate Prof. Dr. Ammad
Hassan Khan for their constructive guidance and suggestions.
I have achieved this work with the prayers of my parents and my wife. Due to their
support, love and encouragement, I worked hard during my research.
Zubair Masoud
2014
iii
ABSTRACT
Geotechnical characterization of soils for its use in any project is conducted through a
programme that comprises in-situ and laboratory tests. The main in-situ tests include
pressuremeters (PMT), Dilatometer (DMT), Standard Penetration Test (SPT), Cone
Penetrometer (CPT). Among these, prebored pressuremeter tests are performed in pre-
drilled boreholes. The drilling methods such as hand augering and rotary drilling rig are
recommended by the ASTM D-4719 for the prebored pressuremeter testing. The vertical
and constant diameter boreholes are the basic requirement for the prebored pressuremeter
testing to obtain quality tests curves. The verticality and constant diameter for the
boreholes are difficult to be achieved by these two methods as the hand auger has no
control on the vertical movement and rotary rig induces vibrations to the walls of the
borehole during rotation of the bit.
A cost effective mechanical drilling system (MDS) has been developed locally for the
drilling of vertical and constant diameter shallow boreholes to about 10 m depth. The
prebored pressuremeter test curves obtained in boreholes drilled by the MDS, hand auger
and rotary rig were compared and found that the quality of the test curves obtained in
boreholes drilled by the MDS was better than the hand auger and rotary rig.
The site selected for the detailed study comprised alluvial soils (CL-ML and ML). In
addition to prebored PMT testing, field testing comprised, SPT, CPT and laboratory
testing included Triaxial testing, Resonant Column along with classification tests.
The sophisticated laboratory testing like resonant column tests, isotropically consolidated
undrained (CIU) and isotropically consolidated drained (CID) triaxial tests with unload-
reload loops were conducted for the determination of shear modulus of soils. The unload,
reload and unload-reload shear moduli from triaxial unload-reload tests were compared
with those determined from pressuremeter tests. The correlations of geotechnical
parameters obtained from laboratory testing and in-situ testing have been established.
The precise determination of the in-situ horizontal stress is difficult by the traditional
prebored PMT testing technique. A new technique has been developed for the estimation
of in-situ horizontal stress keeping in mind the least disturbance/relaxing of the in-situ
stresses.
iv
GEOTECHNICAL CHARACTERIZATION THROUGH PRESSUREMETER AND
LABORATORY TESTING FOR ALLUVIAL SOILS
TABLE OF CONTENTS
Description Page
Dedication i
Acknowledgements ii
Abstract iii
Table of contents iv
List of symbols viii
List of figures ix
List of tables xiii
Chapter-1 Introduction
1.1 General 1
1.2 Objectives 3
1.3 Scope of research 3
1.4 Thesis overview 4
Chapter-2 Geotechnical characterization of alluvial soils
2.1 Introduction 6
2.2 Geotechnical Characterization 6
2.2.1 Soil Deposits 6
2.2.1.1 Alluvial Deposits 6
2.2.1.2 Aeolian Deposits 7
2.2.1.3 Glacial Deposits 7
2.2.1.4 Marine Deposits 8
2.3 Steps of Geotechnical Characterization 8
2.3.1 Drilling for undisturbed /disturbed sampling 8
2.3.2 In-situ and laboratory testing 8
2.3.3 Comparison of In-situ tests 9
2.4 Pressuremeter Testing 12
2.4.1 Definition 12
2.4.2 History of Pressuremeters (PBP, SBP and PIP) 12
v
2.4.3 Main Features of Pressuremeters 13
2.4.4 Types of Pressuremeters 15
2.4.4.1 The prebored pressuremeter 15
2.4.4.2 The Self Boring Pressuremeter 16
2.4.4.3 The Pushed-in Pressuremeters (PIP) 18
2.4.5 Installation techniques 19
2.4.5.1 The Prebored pressuremeter (PBP) 19
2.4.5.2 Self-boring Pressuremeters (SBP) 25
2.4.5.3 Pushed-in Pressuremeters (PIP) 26
2.4.6 Pressuremeter Test Curve 27
2.4.7 Calibrations 30
2.4.7.1 Calibration of Displacement Transducer 30
2.4.7.2 Calibration of Pressure Transducer 30
2.4.7.3 Calibration of Membrane for Stiffness 30
2.4.8 Prebored Pressuremeter Test Procedure 31
2.5 Shear Modulus 32
2.5.1 Shear Modulus from Pressuremeter 32
2.5.2 Non-linear Stiffness Profile 34
2.5.3 Degradation of Shear Moduli 35
2.6 Measurement of In-situ Horizontal Stress (h) 37
2.6.1 Lift-off method 39
2.6.2 Method based on Shear Strength 41
2.7 Determination of Shear Strength of Soil 42
2.8 Determination of Limit Pressure (PL) 43
2.9 Laboratory Testing 44
2.9.1 Soil Classification Tests 44
2.9.2 Strength Tests 45
2.9.2.1 Isotropically Consolidated Undrained (CIU) 45
Triaxial Test
2.9.2.2 Isotropically Consolidated Drained (CID) 46
Triaxial Test
2.9.2.3 Stiffness of Soil from CIU and CID 46
Triaxial Test
vi
2.9.2.4 Comparison of Stiffness from PMT and 48
Triaxial Tests
2.9.2.5 Comparison of static and dynamic stiffness 50
2.9.2.6 Resonant Column Testing 51
2.9.2.7 Unconfined Compression Test (UCT) and 52
Direct Shear Tests
2.9.2.8 Correlations Developed by other Researchers 52
2.10 Summary 53
Chapter-3 Development of Drilling System, In-situ Testing and
Laboratory Testing
3.1 Introduction 55
3.2 Development of Mechanical Drilling System (MDS) 55
3.2.1 Salient Features of Mechanical Drilling System (MDS) 55
3.2.2 Drilling with the MDS 57
3.3 Drilling With Hand Auger 60
3.4 Drilling With Rotary Rig 60
3.5 Verticality of Boreholes 60
3.6 Smoothness of Diameter of Boreholes 63
3.7 Development of New Technique for the Determination of 64
In-situ Horizontal Stress
3.8 In-situ Testing Plan 69
3.9 In-situ Testing 71
3.9.1 Pressuremeter Testing 71
3.9.1.1 Pressuremeter Calibrations 73
3.9.1.2 PMT Test Methodology 77
3.9.1.3 PMT Test Results 79
3.9.2 Cone Penetration Testing (CPT) 80
3.9.2.1 CPT Apparatus 80
3.9.2.2 CPT Test Methodology 80
3.9.3 Standard Penetration Testing (SPT) 81
3.10 Laboratory Testing 82
3.10.1 Preservation of Samples 82
3.10.2 Undisturbed Specimen Preparation 82
vii
3.10.3 Triaxial Tests 85
3.10.4 Triaxial Tests with Unload-reload Loops 86
3.10.5 Resonant Column Tests 88
3.10.6 Unconfined Compression Tests 90
3.10.7 Direct shear tests 90
3.10.8 Soil Classification Tests 90
3.10.9 Soil Profile 95
3.11 Summary 95
Chapter-4 Analysis and Discussion on Results
4.1 Introduction 97
4.2 Comparison of Quality of PMT Curves 97
4.3 Shear Modulus 101
4.3.1 Secant Shear Moduli (Gur , Gu and Gr) from PMT 101
4.3.2 Secant Shear Moduli (Gur , Gu and Gr) from Triaxial 104
4.3.3 Comparison of Shear Moduli from PMT and Triaxial 109
Tests
4.4 Correlations of PMT and Resonant Column Data 113
4.5 Limit Pressure 116
4.6 In-situ Horizontal Stress (ho) 120
4.6.1 Comparison of Traditional and New Techniques for ho 122
4.7 Shear Strength 124
4.8 Summary 125
Chapter-5 Conclusions and Recommendations
5.1 Introduction 126
5.2 Conclusions 126
5.3 Recommendations for Future Research 129
References 130
Appendix A (CPT Profiles) 136
Appendix B (SPT Profiles) 143
Appendix C (Resonant Column Tests - G/Gmax and Damping Ratio) 146
viii
LIST OF SYMBOLS
A list of all the special symbols used in this thesis along with their brief description is
given below:
Symbol Description
CPT Cone penetration test
c Cohesion of soil
′ Angle of internal friction of soil (effective)
DH Borehole diameter
Eur Unload-reload Modulus of elasticity
G Shear modulus
Gmax Maximum shear modulus
Gr Reload shear modulus based on reloading curve
Gs Secant shear modulus
Gu Unload shear modulus based on unloading curve
Gur Unload-reload shear modulus based on unload-reload loop slope
HET Hall effect transducer
N Standard penetration test blow count, Blows/ft
NMC Natural Moisture Content
NP Non-plastic
PBP Prebored pressuremeter
PIP Pushed-in Pressuremeter
p′ Effective stress at the start of unloading
PL Limit pressure
plm Ménard limit pressure
Rf Friction Ratio
SBP Self-boring pressuremeter
SPT Standard penetration test
Su Undrained shear strength
Su(UCT) Undrained shear strength from unconfined compression test
Su(PMT) Undrained shear strength from pressuremeter test
ε Strain
εc Cavity strain
εcurr Current cavity strain
ν Poisson‟s Ratio
σ′ Mean effective stress
σho Total horizontal in-situ stress
ix
LIST OF FIGURES
Chapter-2 Page
Figure 2.1 Types of in-situ and laboratory tests (after Clarke, 1995) 9
Figure 2.2 Definition of Pressuremeter (after Clarke, 1995) 12
Figure 2.3 Main features of pressuremeter (after Clarke, 1995) 13
Figure 2.4 Details of probe (prebored pressuremeter) 14
Figure 2.5 The control unit and pressure supply 15
Figure 2.6 Types of prebored pressuremeters (a) a tricell probe 16
(b) a monocell probe (after Clarke, 1995)
Figure 2.7 Self-boring pressuremeter (SBP) (after Clarke, 1995) 17
Figure 2.8 Pushed-in pressuremeter (PIP) (after Clarke, 1995) 18
Figure 2.9 Typical expansion curves for the pressuremeters 28
(a) the prebored pressuremeter (b) the self-bored pressuremeter and
(c) the pushed-in pressuremeter (after Clarke, 1995).
Figure 2.10 The unload-reload loop showing the lines to calculate the 32
Gu, Gr and Gur.
Figure 2.11 The elastic limit of clays on unloading for pressuremeter test curve 33
Figure 2.12 Elastic limit of sands on unloading of the pressuremeter test curve 34
Figure 2.13 Variation of secant moduli with strain from unload-reload loops of 35
PMT
Figure 2.14 The variation of secant shear modulus with strain for PMT in 36
London clay
Figure 2.15 The reference datum on PIP, SBP and PBP test curves 38
Figure 2.16 A typical PBP curve showing reference datum and insitu horizontal 39
Stress
Figure 2.17 Shapes of initial portion of the SBP curves due to drilling techniques 40
Figure 2.18 Pressuremeter curves based on different reference datum points 41
Figure 2.19 Determination of Su from SBP pressuremeter test in clay 43
(after Clarke, 1995)
Figure 2.20 A typical PBP curve showing the limit pressure 44
Figure 2.21 Stress-strain curve q Vs in monotonic triaxial test with 47
unload-reload loop
Figure 2.22 Unloading-reloading modulus of soil in triaxial compression test 48
x
Figure 2.23 Comparison of secant moduli determined from pressuremeter and 50
triaxial
Chapter-3
Figure 3.1 Mechanical Drilling System (MDS) 56
Figure 3.2 Slotted type sampler 58
Figure 3.3 Helical type sampler 58
Figure 3.4 Regular diameter and smooth surface borehole drilled by MDS 59
Figure 3.5 Longitudinal section of borehole 59
Figure 3.6 Inclinometer and MDS apparatus at site 61
Figure 3.7 Setting of Inclinometer Apparatus 62
Figure 3.8 Inclinometer testing at site 62
Figure 3.9 Displacement of borehole walls from vertical drilled by MDS, RR 63
and HA
Figure 3.10 Typical profile of diameter of boreholes drilled by MDS, RR and HA 64
Figure 3.11 Stain-less steel casing with toothed end for insertion 67
Figure 3.12 The PMT probe inserted in casing from upper end 67
Figure 3.13 The sampler being inserted in casing for drilling of borehole 68
Figure 3.14 The PBP probe being inserted in casing for test 68
Figure 3.15 Typical PMT test curves at different depths by New Technique 69
Figure 3.16 Test points location plan 70
Figure 3.17 Prebored pressuremeter apparatus (Rehman, 2010) 72
Figure 3.18 Details of Electronic Box 72
Figure 3.19 Details of pressure regulating system 73
Figure 3.20 Pico Logger Connections 73
Figure 3.21 Calibration of pressure transducer for different degrees of attenuation 74
Figure 3.22 Calibration of Hall Effect Transducer (HET) 75
Figure 3.23 Calibration of membrane for stiffness 76
Figure 3.24 Pressuremeter Testing at Site 78
Figure 3.25 Typical PMT curves from 1m to 3m depths 79
Figure 3.26 Typical PMT curves from 4m to 10m depths 80
Figure 3.27 Disturbed sample from SPT sampler 81
Figure 3.28 Split mould with membrane attached vacuum system 84
xi
Figure 3.29 Assembled split mould with base collar and cutter 84
Figure 3.30 Mechanical extruder with mould and cut piece of Shelby tube 85
Figure 3.31 The Triaxial test in progress 86
Figure 3.32 Typical stress-strain curves of CIU triaxial test with unload-reload 87
loops for CL-ML soil
Figure 3.33 Typical stress-strain curves of CID triaxial test with unload-reload 87
loops for ML soil
Figure 3.34 Resonant column apparatus used for testing 88
Figure 3.35 Resonant column test in progress 89
Figure 3.36 Typical resonant column test data 89
Figure 3.37 Soil profile at site 95
Chapter-4
Figure 4.1 Phases of a good quality prebored pressuremeter curve 98
Figure 4.2 Typical PMT curves in CL-ML soil by RR, MDS and HA 99
Figure 4.3 Typical PMT curves in ML soil by RR, MDS and HA 99
Figure 4.4 Method for the calculation of secant moduli Gsu(PMT) and Gsr(PMT) 102
Figure 4.5 Typical unload–reload loops (1 & 2) of PMT for CL-ML soil at 102
3m depth
Figure 4.6 Typical unload–reload loops (1 & 2) of PMT for ML soil at 9m depth 103
Figure 4.7 Profiles of Gur (PMT) 104
Figure 4.8 Typical unload-reload loops (1, 2, 3 & 4) of static triaxial (CIU) test 106
for CL-ML soil at 2m depth
Figure 4.9 Typical unload-reload loops (1, 2, 3 & 4) of static triaxial (CID) test 107
for ML soil at 4 m depth
Figure 4.10 Profile of Gur (TXL) 108
Figure 4.11 Gur (PMT) & Gur (TXL) vs. shear strain for CL-ML soil 109
Figure 4.12 Gur (PMT) & Gur(TXL) vs. shear strain for ML soil 110
Figure 4.13 Gu (PMT) & Gu (TXL) vs. shear strain for CL-ML soil 110
Figure 4.14 Gr (PMT) & Gr (TXL) vs. shear strain for CL-ML soil 111
Figure 4.15 Gu (PMT) & Gu (TXL) vs. shear strains for ML soil 111
Figure 4.16 Gr (PMT) & Gr (TXL) vs. shear strain for ML soil 112
Figure 4.17 Gmax(RC) vs. effective stress for CL-ML soils 114
Figure 4.18 Gmax(RC) vs. effective stress for ML soils 114
xii
Figure 4.19 Correlation of Gmax from resonant column and Gur from PMT for 115
CL-ML soils
Figure 4.20 Correlation of Gmax from resonant column and Gur from PMT for 115
ML soils
Figure 4.21 Determination of limit Pressure from PMT curve 116
Figure 4.22 Profiles of limit pressures 117
Figure 4.23 Correlation of PL(PMT) and Gur(TXL) for CL-ML soil 117
Figure 4.24 Correlation of PL(PMT) and Gur(TXL) for ML soil 118
Figure 4.25 Correlation between Qc from CPT and limit pressure from PMT for 118
CL-ML soils
Figure 4.26 Correlation between Qc from CPT and limit pressure from PMT for 119
ML soils
Figure 4.27 Correlation between PMT limit pressure and SPT N value for 119
CL-ML soils
Figure 4.28 Correlation between PMT limit pressure and SPT N value for 120
ML soils
Figure 4.29 The plots of loading portion of PMT curve at different datum strains 121
at 4m depth
Figure 4.30 In-situ horizontal stress of CL-ML and ML soils 122
Figure 4.31 PMT test curves by traditional and new technique 123
Figure 4.32 ho from Traditional Technique (TT) and New Technique (NT) 124
Figure 4.33 Correlation of Su(PMT) and Su(UCT) 125
xiii
LIST OF TABLES
Chapter-2 Page
Table 2.1 The applicability and usefulness of in-situ tests 11
(after Robertson, 1986 and Wroth, 1984)
Table 2.2 Applicability of pressuremeters to different ground conditions 19
Table 2.3 Standard methods for creating test pockets for pressuremeter 21
(after Finn et al., 1984, ASTM D4719-87, Amar et al., 1991)
Table 2.4 Parameters obtained from different pressuremeter tests 29
Table 2.5 Empirical relations between undrained shear strength and net limit 42
pressure for different soils (after Clarke, 1995)
Chapter-3
Table 3.1 Schedule of In-situ tests and UDS 71
Table 3.2 Summary of Soil Classification, NMC, Dry Density, Unconfined 91
Compression and Direct Shear Test Results (Location 1)
Table 3.3 Summary of Soil Classification, NMC, Dry Density, Unconfined 92
Compression and Direct Shear Test Results (Location 2)
Table 3.4 Summary of Soil Classification, NMC, Dry Density, Unconfined 93
Compression and Direct Shear Test Results (Location 3)
Table 3.5 Summary of Soil Classification, NMC, Dry Density, Unconfined 94
Compression and Direct Shear Test Results (Location 4)
Chapter-4
Table 4.1 Comparison of Different Modes of Drilling in Soil 100
Chapter-5
Table 5.1 Correlations proposed 128
CHAPTER-1
1
INTRODUCTION
1.1 GENERAL
The geotechnical characterization is a process of diagnosis of soils to discover the
properties of certain strata by in-situ and laboratory testing. The geotechnical
characterization of soils is the basic requirement for the planning, geotechnical design,
management of operations for the construction project and long term performance of the
structures. The soil properties are needed to be explored for the assessment of behaviour
of soil during and after completion of construction. Site characterization includes soil
investigation through drilling, sampling, field testing, laboratory testing and establishing
correlations of geotechnical parameters determined from different tests. Hight and
Leroueil (2003) have described that the level of precision of geotechnical site
characterization depends upon the previous experience of the site, design objectives; risk
involved in geotechnical investigation and funds available.
The present research includes drilling, sampling, in-situ testing and laboratory testing for
the geotechnical characterization of alluvial soils. Alluvial soils consist of a broad
spectrum of soils regarding the types and the conditions at site. As the alluvial soils are
frequently found in the world, hence the geotechnical characterization of the alluvial soils
and establishing the correlations between geotechnical parameters for alluvial soils is
very important.
The first step is the assessment of expected soil stratigraphy of the site to be characterized
by the survey of the site. This assessment may be conducted with the help of observations
from the previous studies of the site. The expected stratigraphy helps in choosing the
mode of drilling and the drilling equipments. After the collection and evaluation of
available information about the site, the field exploration methods, frequency of
sampling, frequency and type of field tests are planned according to the need of the
project design. The investigation plan is prepared for the locations of the test points. The
drilling equipment is shifted on site and the drilling activities are planned. The drilling
points are marked at site according to the need of the design for different structures to be
built at site. The number and depth of boreholes along with minimum spacing between
CHAPTER-1 INTRODUCTION
2
the boreholes depends upon the type of the structure and expected variability of the strata.
The number of boreholes may vary according to the condition of the recovered samples.
If there is large extent of variability in the strata, the depth and the number of boreholes
may be increased to collect maximum data of the site for precise geotechnical design. The
drilling plans are always flexible and are immediately changed according to the variations
encountered in the strata.
Undisturbed sampling of soil is the most important step for the precise and quality
laboratory testing. The undisturbed samples are used to determine the strength and
stiffness of soil in resonant column, triaxial and direct shear tests. Thin-walled Shelby
tubes are used for the sampling of cohesive soils. The sample tubes are then transported
with great care so that the samples may not be disturbed during transportation to the
testing laboratory. The samples are placed in a room with controlled humidity so that the
natural moisture content of the soil samples may not vary. The costly and large extent of
inaccuracies may be encountered in geotechnical design of structures if the soil samples
from the site are not recovered, transported and stored according to standards. The depth
and frequency of the recovery of undisturbed samples depend upon the nature of the
structure to be constructed at site.
The in-situ testing is conducted along with the drilling activities. The in-situ tests can be
used to obtain the profiles of geotechnical properties at site. For economic reasons the in-
situ testing plays very important role in large construction projects where time is an
important factor for feasibility of the project. As regards the cost of in-situ testing and the
total cost of the project, the in-situ tests are preferred especially at those sites where the
undisturbed sampling of the subsurface is difficult. The in-situ investigation techniques
are used for the evaluation of geotechnical properties of soils in relatively undisturbed or
in-situ conditions of strata. Some times construction of the embankments is monitored by
the in-situ tests and the results of these tests can be used frequently at site to save the
precious time of the project.
The pressuremeter testing is very precise mode of in-situ testing which is used to evaluate
shear modulus, undrained shear strength, angle of internal friction, insitu horizontal stress
and limit pressure of soils. Other popular geotechnical insitu tests like CPT and SPT may
also be conducted on site to validate the parameters obtained from the pressuremeter tests.
CHAPTER-1 INTRODUCTION
3
The performance of standard laboratory soil testing is time consuming which delays the
projects for considerable time. Although the laboratory testing is very necessary for
precise determination of geotechnical parameters but it is very costly. It can be conducted
for the validation of results obtained from in-situ testing and for the development of
correlations between sophisticated laboratory testing and standard in-situ tests like PMT,
CPT and SPT so that the soil strata may be characterized in the field without proceeding
to costly and time consuming processes like drilling, sampling, transportation of samples,
precise sample preparation procedures and sophisticated laboratory testing.
1.2 OBJECTIVES
The objectives of the research were set as follows
a) To develop a mechanical drilling system for making the shallow depth vertical
boreholes in soil.
b) To test the pressuremeter as Prebored pressuremeter in alluvial soils.
c) To perform laboratory testing on the undisturbed and disturbed soil samples extracted
from boreholes.
d) To develop correlations of geotechnical parameters based on in-situ pressuremeter
testing and laboratory testing.
1.3 SCOPE OF RESEARCH
To achieve objectives of the research work stated above, following scope of work was
undertaken:
Literature survey related to the geotechnical characterization of alluvial soils from
books on geotechnical investigations and fabrication of geotechnical instruments.
The mechanical drilling system was fabricated using resources available in the local
market. The main features incorporated in mechanical drilling system were verticality
during the drilling and to ensure constant diameter of the borehole. Slotted type and
helical samplers of special sizes were also fabricated for drilling boreholes.
CHAPTER-1 INTRODUCTION
4
The site comprising alluvial soils was selected for the study. In-situ tests including
pressuremeter testing, CPT and SPT were conducted at the site and the laboratory
tests including triaxial (CIU and CID) tests with unload-reload loops, resonant column
tests, direct shear tests, unconfined compression tests and classifications tests were
conducted on the samples recovered from the boreholes in thin-walled tubes.
A comparison has been made of the results of the pressuremeter tests conducted in the
boreholes drilled by MDS with hand auger and rotary drilling rig.
An apparatus was also fabricated for the determination of in-situ horizontal stress
using a new technique during prebored pressuremeter testing.
The shear modulus degradation curves of triaxial and pressuremeter tests were
compared and the correlations between static tests (triaxial and pressuremeter) have
been established.
Correlations between static test (pressuremeter test) and dynamic test (resonant
column test) have also been established.
1.4 THESIS OVERVIEW
The research work is presented in five chapters. A brief description of each chapter is
given below:
Chapter-1 presents the importance of geotechnical characterization, tests to be carried out
at site and laboratory for the characterization of soils. Objectives and scope of research
work are also included in this chapter.
Chapter-2 presents the detailed literature study for the methods of geotechnical
characterization including in-situ and laboratory testing. The different types of
pressuremeters with installation techniques in soils are described. The methods of
interpretation of geotechnical parameters from prebored pressuremeter are described in
detail.
Chapter-3 presents the methodology and results of in-situ and laboratory tests. The in-situ
tests include prebored pressuremeter tests with traditional and new techniques, cone
penetration tests (CPT) and standard penetration tests (SPT). The laboratory tests include
CHAPTER-1 INTRODUCTION
5
triaxial (CU and CD) tests with unload-reload loops, resonant column tests, direct shear
tests, unconfined compression tests and classification tests.
Chapter-4 presents the analysis, comparison and development of correlations between
pressuremeter and laboratory testing data. Discussions on the in-situ and laboratory
results are also included in this chapter.
Chapter-5 presents conclusions of research work and recommendations for future
research.
Appendix–A includes CPT profiles.
Appendix–B includes SPT profiles.
Appendix–C includes Resonant Column Tests (G/Gmax and Damping Ratio).
CHAPTER-2
6
GEOTECHNICAL CHARACTERIZATION OF ALLUVIAL SOILS
2.1 INTRODUCTION
Soils can be categorized based on the results of field tests (e.g. pressuremeter, CPT and
SPT) and laboratory tests (e.g. triaxial tests with unload-reload loops, resonant column
dynamic test, direct shear test, unconfined compression tests and classification tests). This
chapter describes details of the field and laboratory methods including interpretation of
the results in order to understand the state and type of soils at a particular project.
2.2 GEOTECHNICAL CHARACTERIZATION
The first step in geotechnical design is to know the soil properties of soils at a site for the
specific purpose. Basically the soils are classified in two groups i.e. cohesive and
cohesionless soils. The cohesionless soils comprise sands, silts and gravels. The cohesive
soils comprise clays and plastic silts. Geotechnical characterization for soils is conducted
for the assessment of variations in ground type, soil properties determined in laboratory
from index tests, shear strength tests, soil dynamic tests and soil properties determined
from in-situ tests like pressuremeter test, standard penetration tests and cone penetration
test. Fig.2.1 shows the common in-situ (field) and laboratory tests used to characterize
the ground strata.
2.2.1 Soil Deposits
The soil deposits which have similar origin and mode of depositions, show comparable
geotechnical properties which can be used for the structures to be built on these deposits.
The major soil deposits are described as below.
2.2.1.1 Alluvial Deposits are formed due to the soil sedimentation caused by the
flowing water. The alluvial soils can be deposited by lake or river and are found all over
the world. Alluvial soils are usually fine grained silty-clay / clayey silt, silt, clay and fine
to medium sands.
The alluvial deposits formed due to the flood water are floodplain deposits. The
floodplain deposit includes point bar, channel fill and back swamp. The point bar is
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
7
formed by alternate deposits of ridges and swales. The ridges are composed of sand and
silt and swales consist of clay. The point bar soils show favorable foundation conditions.
Channel fill are composed primarily of clay and are formed in meander loops due to the
course shortening process of the river. The silty and sandy soils in the channel fill
deposits are also found at the upstream and down stream points. Fine-grained soils of
channel fill show compressible nature.
The back swamp is the sedimentation due to flood water in flood basins. The nature of
this deposit is generally clay. The deposition of the soil is usually uniform in horizontal
direction.
The alluvial terrace deposits are flood-plain deposits formed by entrenchment of the river.
They also show favorable foundation conditions. Alluvial-lacustrine deposits are formed
within lakes consisting of clay at the mid of the lake and the sandy/ silty nature at the
boundary of the lake. The alluvial-lacustrine deposits are generally very uniform in the
horizontal direction. The deltaic deposits are formed at the mouth of the river and consist
of fine-grained compressible soils.
If a deposit comprises clay and silt layers, it is called as varved clay. Alluvial soils
generally show compressibility as these are usually soft soils.
2.2.1.2 Aeolian Deposits are formed by the soil which is transported and deposited by
wind. Aeolian deposits are of two types; loess and dune sands. Loess comprises silts or
sandy silts or clayey silts. Loess shows collapsible structure but composed of uniform
deposition. The dune sands are mounds and ridges of uniform fine sands. The main
characteristic is the uniform grain size. The dune sands are in relatively loose condition.
2.2.1.3 Glacial Deposits are formed by the soils transported and deposited by the
glaciers or by melting water of glaciers. The glacial deposits are of three types; glacial
till, glacio-fluvial deposit and glacio-lacustrine deposit. The glacial till is the debris which
is collected at the side or beneath the glacier and consists of soil of all sizes ranging from
boulders and gravels to clay. The glacio-fluvial deposits are formed by the streams of
melt water and consist of coarse and fine-grained material. The glacio-lacustrine deposits
are formed in lakes by melt water of glaciers.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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8
2.2.1.4 Marine deposits are formed by soils transported and deposited by ocean waves.
These deposits are laid in shore and offshore areas. The deposits formed by waves on the
shoreline consist of sands and/or gravels. The depositions of organic and inorganic fine-
grained material are called as marine clays.
2.3 STEPS OF GEOTECHNICAL CHARACTERIZATION
Following are the main steps for characterization of soils:
Drilling for undisturbed/disturbed soil sampling.
In-situ and laboratory testing.
2.3.1 Drilling for undisturbed /disturbed sampling
The rotary drilling is the common drilling technique used for the undisturbed sampling of
soils. The rotary rig is shifted on site with the accessories related to the sampling of soil
expected to be encountered i.e. clay, sand etc. For clayey and sandy strata, thin walled
tubes are used for the recovery of undisturbed samples. The samples are transported from
site to laboratory according to ASTM recommended procedures. The boxes for the
preservation of the sample tubes are also fabricated according to ASTM procedure.
Disturbed samples are commonly recovered by standard penetration tests. These samples
are preserved in plastic jars with proper identification on the jars. The jars are sealed and
transported to the laboratory for the classification tests and chemical test as these tests can
be conducted on the disturbed samples. The number of disturbed samples recovered by
SPT is more than the undisturbed samples. Hence the extent of characterization tests is
very important on disturbed samples.
2.3.2 In-situ and laboratory testing
There are different in-situ and laboratory methods of determining geotechnical properties
of soils. The in-situ tests conducted in the boreholes include pressuremeters,
penetrometers and geophysical methods. The laboratory testing includes triaxial,
unconfined, and direct shear tests which are frequently conducted for the soil
characterization.
Following is the detailed scheme of in-situ and laboratory tests for the geotechnical
characterization of soils (Fig. 2.1).
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
9
Fig.2.1: Types of in-situ and laboratory tests (after Clarke, 1995)
2.3.3 Comparison of In-situ tests
Robertson (1986) and Wroth (1984) described the usefulness and the applicability of the
in-situ tests. Table 2.1 shows the comparison of different in-situ tests in different types of
soils and shows a variety of field tests for a wide range of ground strata i.e. hard rock to
peat and geotechnical parameters obtained from these tests are also mentioned.
It is observed from Table 2.1 that pressuremeter is the only instrument that can be used
for a wide range of strata. The penetrometers are not suitable for use in hard rocks. The
only prebored pressuremeter among the series of all pressuremeters can be used in hard
rock as it is very difficult for the self boring pressuremeter to drill into the hard rock. The
prebored pressuremeter can also be used in gravel. In sand, silt, clay and peat strata,
almost all types of pressuremeters can be used.
Laboratory In-situ
Tests
Element Model Non
Destructive Full Scale Borehole
Triaxial
Direct
Shear
Computer
Centrifuge
Surface Pile tests
Instrumented
embankments
Penetrometers Pressuremeter
Static cone
Dynamic cone
DMT
Menard
PBPM
SBPM
FDPM
Permeability Others Instrumentation
Falling Head
Constant head Vane
Cross-hole Geophysics
Plate
Piezometer
Spade Cells
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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10
Among the penetrometers, SPT is widely used in variety of soils although the number of
parameters obtained from SPT are less than other penetrometers. The seismic cone
(SCPTU) and piezocone (CPTU) are very sophisticated and important techniques by
which large number of geotechnical parameters can be obtained in a variety of soils.
Hence, the in-situ tests can provide variety of geotechnical parameters in variety soils
which is very important aspect in geotechnical investigations as almost all types of soils
can be investigated in-situ. The simulation of in-situ conditions in the laboratory is costly
and time consuming. Hence the in-situ testing at site is preferable.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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11
Table 2.1 The applicability and usefulness of in-situ tests (after Robertson, 1986 and Wroth, 1984)
Group Device Parameters Ground Type
Soil Profile u Φ′
su
Dr mv cv k G σh OCR σ ε
Har
d R
ock
Soft
rock
Gra
vel
San
d
Sil
t
Cla
y
Pea
t
Penetrometers Dynamic C A - C C B - - - C C C - C B A B B B
Mechanical B A - C C B C - - B C C - C - A A A A
Static (CPT) B A C C B C - - B C C - - C - A A A A
Piezocone (CPTU) A A A B B A B A B B C A B C - A A A A
Seismic (SCPTU) A A A B B A B A B A B A B - C - A A A A
Flat Dilatometer
(DMT) B A C B B C B - B B B B - C A A A A
Acoustic Probe C B - C C B C - - C - C C - A A A A
SPT B B - C C B - - - - - - C B A A A A
Resistivity Probe B B - B C A C - - C - - - C - A A A A
Pressuremeters PBP B B - C B C B C - B C C C A A B B B A B
SBP B B A A A A A A B A A A A - A - B A A A
PIP A B B C B C C A B A C C C - - - B A A B
Cone PIP C B B C B C C A B A C C C - - A A A A
Others Vane B C - - A - - - - - - - - B A B
Screw plate C C C B B B C C A C B B - - - A A A A
Plate C - - C B B B C C A C B B B A B B A A A
Borehole permeability C - A - B A - - - - A A A A A A B
Hydraulic Fracture - B - - - - C C - B - B B C C B A C
Crosshole/downhole/
surface seismic C C - - - - - A - - B A A A A A B A
Applicability: A high; B-moderate; C-low; - not.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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12
2.4 PRESSUREMETER TESTING
2.4.1 Definition
Pressuremeter is a cylindrical probe for the application of uniform pressure on the
borehole walls by a flexible membrane (Clarke, 1995) as shown in Fig. 2.2.
Pressuremeter is one of the premier tests used world wide to assess the in-situ shear
stiffness (G) of soils (Clarke, 1995). The pressuremeter membrane is expanded when the
pressuremeter is installed in the borehole at any desired level of depth for the
determination of geotechnical parameters. The portion comprising membrane is called
test module whereas control system is on the ground surface. The data logger is attached
with the control system. The control cable and the hose for the gas pressure are attached
with the probe.
Fig.2.2: Definition of Pressuremeter (after Clarke, 1995)
2.4.2 History of Pressuremeters (PBP, SBP and PIP)
The first evidence of pressuremeter is from Kogler in 1933. Modern pressuremeter was
first developed by Louis Menard in 1955 and was known as Menard pressuremeter. It was
first used in Chicago (Menard, 1957). The Menard pressuremeter is the prebored
pressuremeter (PBP) and is still widely used in geotechnical investigations in the world
for the determinations of ground properties. Louis Menard also developed design method
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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13
based on the pressuremeter which is unique. This approach is also called as Menard‟s
method. Menard also developed design charts for the pressuremeter results Clarke, 1995).
According to Jezequel et al. (1968), a method should be devised to install the
pressuremeter probe without altering the geotechnical properties of the ground. For this
purpose the self boring pressuremeter (SBP) was developed. Pushed-in pressuremeters
(PIP) were introduced in 1980s to overcome the difficulties of installation of SBP.
2.4.3 Main Features of Pressuremeters
The main features of a pressuremeter are shown in Fig. 2.3, which are common to all
pressuremeters. The pressuremeter consists of three main parts i.e. probe, control unit and
cable with connections.
Fig.2.3: Main features of pressuremeter (after Clarke, 1995)
Section “A” is the probe which includes the installation section (D), test section (E) and
the section “F” which can be void or drilling module. Section “B” is the control unit
which includes the data logger and electronics box. Section “C” consists of drill rods and
control cable. The detailed section of the probe is shown in Fig.2.4. The protective sheath
is provided to protect the membrane. The membrane rings are used to clamp the
membrane.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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14
Fig.2.4: Details of probe (prebored pressuremeter)
The membrane of the pressuremeter probe during the test is expanded to stress the walls
of the borehole uniformly. If the voids or cracks encounter in the strata during the test, the
membrane expands in the void or crack and bursts. To avoid this burst, a protective
sheath of metal strips is installed on the membrane to conduct the test in non-uniform or
layered strata having much difference in stiffness. Corrections are applied to the stress for
membrane and sheath separately. The outward movement of the membrane is measured
by the radial displacement transducer i.e. Hall effect transducer (HET) in case of radial
displacement type pressuremeter, and by measuring the volume of the water or oil forced
into the probe in case of volume displacement type pressuremeter. The hydraulic hose is
used for pressurized gas to enter into the probe. Core tube is the steel tube on which the
membrane is installed. The installation section is a hollow closed end cylinder.
The control unit consists of pressure control system, data logger and electronics box
(measuring unit) as shown in Fig. 2.5. The pressure control system further comprises
pressure control valves, pressure regulators and pressure delivery pipes. The electronics
box consists of electronic circuits with voltage variable system. The data logger transmits
the data to the computer where the pressure and displacement readings are displayed and
stored in the computer. The pressuremeter tests may be stress controlled or strain
controlled. In stress controlled tests, the strain or volume of the membrane is measured
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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15
and in case of strain controlled tests, the pressure of the gas is measured. Usually the
pressurized nitrogen gas is available in cylinders.
Fig.2.5: The control unit and pressure supply
2.4.4 Types of Pressuremeters
There are three main types of pressuremeters i.e. PBP, SBP and PIP depending upon the
installation techniques as shown in Figs. 2.6, 2.7 and 2.8.
2.4.4.1 The Prebored Pressuremeter (PBP) is the most common type of pressuremeters
which is easy to use at site. The prebored pressuremeter is placed in the borehole
predrilled for this purpose. The first prebored pressuremeter is Menard pressuremeter. It
has three expanding cells hence it is known as tricell probe (Fig. 2.6). The central cell is
called as test section which is of volume expansion type and the other two cells are guard
cells expanded to ensure the cylindrical shape of the test section. The Menard
pressuremeter is lowered in the borehole whose diameter is slightly larger than the outer
diameter of the pressuremeter probe. There is stress relief to the walls of the borehole
after drilling before installation of the prebored pressuremeter. Additional interpretation is
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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16
necessary for the consideration of installation effects of PBP. In 1950s the single cell or
mono cell pressuremeter was developed by OYO Corporation of Japan.
Fig.2.6: Types of prebored pressuremeters (a) a tricell probe (b) a monocell probe
(after Clarke, 1995)
Prebored pressuremeters can be used in any ground conditions from soft to stiff or dense
soils. In rocks, the prebored pressuremeters are used as the predrilled borehole is required
for this purpose.
2.4.4.2 The Self Boring Pressuremeter (SBP) was proposed to be an effective
instrument for the measurement of true response of relatively undisturbed ground in-situ
by Jezequel et al. (1968). The principle of the SBP is that there should be no change of
stress at the leading face of the self boring probe so that there may be least disturbance to
the soil surrounding the probe.
(a)
(b)
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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17
Fig.2.7: Self boring pressuremeter (SBP) (after Clarke, 1995)
A typical SBP is shown in Fig. 2.7. The test section may be volume or radial
displacement type. Different self boring systems have used which include drilling, jetting
or replacing type. The fluid passes through the hollow core tube. The core tube also
transmits the vertical force to provide the downward thrust for drilling. The drilling head
attached to the probe is an internally chamfered shoe for the drilling purpose. The SBP
was developed to be used in soils but it can also be used in weak or soft rocks if the
drilling system of the probe is sufficiently robust. This type of pressuremeter was
extensively used in France and UK.
There is minimum disturbance to the ground during the installation of the SBP. The SBP
theoretically causes no disturbance to the surrounding soil hence the parameters
determined by this instrument are the properties of soil which are much less affected by
Probe drilled into test pocket
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
18
the installation technique and these properties can be used in any precise geotechnical
analysis. It is very difficult to install the SBP, as much care and expertise are required for
this purpose.
2.4.4.3 The Pushed-In Pressuremeters (PIP) are pushed into the soil (Fig. 2.8) and the
test is conducted at different depths. If the soil is fully displaced during pushing of the
probe, the pressuremeter is called as full displacement pressuremeter (FDP).
The pushing phenomenon is like the penetrometers. The jacking force required to
penetrate the pressuremeter into the soil depends upon the friction of the probe with soil
and the resistance of the cone attached at the lower end in case of full displacement type.
Jezequel et al. (1982) developed a pressio-penetrometer for testing of off-shore soils. A
10cm2 piezocone was attached with this pressuremeter consisting of volume displacement
type monocell probe having pressure capacity of 2.5MPa and 100% volumetric strain.
Withers et al. (1986) proposed a FDP of 44mm diameter and 1m long probe.
A Chinese lantern consisting of stainless steel strips is used to protect the membrane as
the resistance of the soil with membrane causes damage or burst of the membrane. The
PIP is used in soil because penetration even in weak rocks is very difficult.
Fig.2.8: Pushed-In pressuremeter (PIP) (after Clarke, 1995)
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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19
2.4.5 Installation Techniques
Different installation techniques are applied for the three types of pressuremeters (PBP,
SBP and PIP). The correct installation techniques are most important for the reliable
results of pressuremeter testing. The minimum disturbance level during pressuremeter
testing is required for reliable and quality test curves which can only be achieved by the
use of suitable and correct installation technique for different pressuremeter probes. The
soil is disturbed due to preboring in case of PBP and due to pressing of soil strata during
penetration in case of PIP. The minimum soil disturbance is observed in case of SBP as
the soil cuttings are removed by the flushing mud and the membrane of the pressuremeter
is almost in touch with the borehole walls. Hence the installation technique adopted by
SBP is well suited for the precise determination of in-situ horizontal stress. However PBP
is well suited for strong rocks as compared with SBP.
Applicability of PMT for different ground types is given in Table 2.2. Standards for the
detailed procedures of site operation are ASTM D-4719-87 and Clarke and Smith (1992).
Table 2.2: Applicability of pressuremeters to different ground conditions
Ground Type PBP SBP PIP
Soft clays A A A
Stiff clays A A A
Loose sands B with support A A
Dense sands B with support B C
Gravels C by driving N N
Weak rock A B N
Strong rock A N N
A, very good; B, good; C, moderate; N, not possible (after Clarke, 1995)
The above table shows that the pressuremeter can be used in any type of ground with
variable conditions.
2.4.5.1 The Prebored Pressuremeter (PBP) can be used in almost all ground types as
mentioned in Table 2.1. The setup of the PBP is shown in Fig. 2.6. The PBP can cause
some disturbance to walls of the predrilled borehole. The walls of the borehole are
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
20
relaxed after drilling as these are not supported by any casing. This stress relief causes the
walls to move inside the borehole due to which the total in-situ stress is changed. The
stress on the wall of borehole will be zero or equal to the pressure of the bentonite mud
being used for drilling. The walls of the borehole are eroded during drilling and the pieces
of the soil fall into the borehole and the soil can fail in extension. This may cause collapse
of the borehole. The pore water pressure of the soil adjacent to the borehole walls
dissipates and the mud softens the walls of the borehole causing disturbance to the fabric
of the soil of the walls. When the drilling bit rotates in the borehole, the vibration and
eccentricity of the drilling bit causes the disturbance to the walls.
The main consideration during the pressuremeter testing is that borehole should be
prepared for the pressuremeter tests only. The borehole diameter is selected according to
the size of the probe. The drilling method is selected keeping in view the expected soil
strata at site. The drilling method should cause the minimum disturbance during up and
down movement of the drilling rods and bit. The resultant diameter of the hole should be
as precise as possible.
Table 2.3 shows that the borehole can be drilled by many drilling equipments/ methods
for the pressuremeter testing. These methods are recommended by ASTM D-4719. The
borehole drilling techniques for clays, silts, sands, gravels and rocks have been described
with suitability of different methods for different strata with different consistency.
The first most task for the prebored PMT is to ascertain the soil profile. By the use of soil
profile, correct drilling technique can be chosen. For this purpose the log of the first
borehole is prepared very carefully at site and the preliminary analysis of the
pressuremeter tests should be conducted at site so that approximate properties of the
ground can be assessed. This assessment is very important for the approximate
application of the pressure and assessment for the readings of the strain.
Hand auger with mud flush is recommended for drilling of boreholes in clays and silts as
the mud flush retains shape of the borehole. For loose soils thick mud flush is used so as
to avoid caving of the borehole walls.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
21
Table 2.3 Standard methods for creating test pockets for pressuremeter (after Finn et al., 1984, ASTM D4719-87,
Amar et al., 1991)
Soil Type Hand
auger
Hand
auger
with
mud
Flight
auger
Driven
sampler
Driven
slotted
tube
Pushed
sampler
Pilot
hole and
pushed
sampler
Pilot
hole and
shaving
Core
barrel
Rotary
percussion
Open
hole
drag
bit
Clays:
Soft 2B 1 NR NR NR 2B 2 2 NR NR 2B
Firm to stiff 1B 1 1B NR NR 1 2 2 NR NR 1B
Stiff to hard NA NA 1B 2 NR 2 1 1 1B NR 1
Silts: Above GWL 1 2 NR 2 NR 2B 2 2B NR NR 1B
Under GWL NR 1 NR NR NR NR NR 2B NR NR 1B
Sands:
Loose and above GWL 2 1 2 2 NR NR NR 2 NA NR 1B
Loose and below GWL NR 1 NR NR NR NR NR 2 NA NR 1B
Medium to dense 1 1 2 2 NR NR NR 2 NR 2B 1B
Sand and
gravel:
Loose NA NA NA NR 2 NA NA NA NA 2 2
Dense NA NA NR NR ID NA NA NA NA 2 NR
Rock: Weathered NA NA NA 1 NR NA 2B NA 1 2 1
Strong Rock NA NA NA NA NA NA NA NA 1 2B 2B
1, recommended; 2, acceptable; NR, not recommended; NA, not applicable; B, conditional; D, pilot hole drilled first.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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22
Continuous flight augers are usually used in stiff clays. These augers should be used with
care so that the upward lifting of the auger may not cause disturbance to the walls of the
borehole. It should be ensured that the soil is cut and not pushed to the side. Very careful
movement of the auger is required. During upward lifting, the auger should be rotated in
the same direction as was being adopted during drilling.
Percussive bits form irregularities in the walls of the borehole; hence these are not
suitable in clays, silts and sands. These bits can be used for rapid drilling of boreholes
between the test points after which other method of drilling may be applied for drilling of
test cavity.
Core barrel can not be used in clays, silts and sands but can be used in sand and gravels
and in rocks. The core barrel can make the precise diameter borehole and the size of the
cuttings is very small which can be flushed with mud very easily.
Pushed samplers can be used in clays to form the test cavities. These can be used in clays
and sands (above ground water table). Pushed sample tubes can be used to form a cavity
at the bottom of the borehole in soils which are self-supporting.
The PBP tests can be conducted in gravelly soil if a slotted casing is inserted into the
gravelly soil and pressuremeter probe is placed in this slotted casing (Baguelin et al.,
1978).
Boreholes can be prepared by hand auger method upto 5m depth (Clarke, 1995).
According to ASTM D-4719 (2000), Iwan type hand auger is recommended for drilling
of shallow boreholes for prebored pressuremeter testing up to maximum depth of 6m in
clayey soil (firm to stiff), silty soils (above GWL), sandy soils (loose and above GWL)
and sandy soils (medium to dense). The hand augering is time consuming but low cost
technique.
When a borehole is drilled with rotary drilling rig, the vibration or eccentric loading of
the moving bit may disturb the walls of the borehole (Clarke, 1995). The cost of drilling
of boreholes by rotary rig is very high as compared to hand augering. The time required
for the transportation for rotary drilling rig, setting of the rig at the drilling point, point to
point shifting and finally the time consumed in drilling of borehole is much more as
compared to hand augering.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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23
There are two methods of installation of the PBP probe in the borehole to conduct the
test. In the first method complete borehole is drilled up to the maximum depth and then
the probe is installed at the specified depth intervals and the tests are conducted. This
method has disadvantages as the borehole walls become soften and pieces of the walls fall
in the borehole resulting in the disturbed surface of the borehole walls. In second method,
the borehole is drilled for one test only and after the test has been conducted, the drilling
of borehole is advanced. The second method has advantage as the freshly drilled soil can
be tested which results in good quality pressuremeter test data. By adopting the second
method, the PBP test can be conducted within 15 minutes of borehole drilling (Mair and
Wood, 1987) to minimize the effects of softening and collapsing of the borehole walls.
Recommended methods for preparation of good quality boreholes are described by
Baguelin et al. (1978), Finn et al. (1984). Boreholes can be drilled by rotary rig, hand
auger, flight auger, percussive method and core barrel. Following are the factors which
affect the selection of the drilling technique for PBP test:
a) Diameter of the borehole
b) Verticality of the borehole
c) Possibility for the collapse of the borehole due to uncased wall.
d) Erosion of the borehole walls due to upward movement of drilling mud.
e) Softening of walls due to water absorbed from drilling mud.
f) Presence of gravels which can cause irregular surface of the wall of borehole.
g) Spacing and depth of PBP tests in the borehole.
The minimum spacing between the test points is usually 1.5 times the probe length so it
may be selected as 1 to 2 m.
The quality of installation of the probe affects results of the pressuremeter. As the pocket
diameter increases or decreases from the ideal range, most of the required information
from the result (test curve) is lost. Hence undersized and too large pockets are considered
as result of low quality drilling. The drilling of quality borehole / pocket is the first step
for the best quality PMT results.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
24
The preparation of the good quality borehole is the basic necessity for quality prebored
pressuremeter tests. The borehole is designed according to the criteria required for hole
size and minimum disturbance. Pressuremeter test can be conducted in prebored
boreholes for obtaining stress-strain pressuremeter curve when the wall of the borehole is
stressed laterally by an expandable flexible membrane. Good quality predrilled borehole
is required for obtaining precise and good quality test curve pressuremeter testing hence
the borehole should be shaped carefully before the test is conducted in the borehole
(Suyama et al. 1982, Briaud and Gambin, 1984, Amar et al. 1991, Clarke 1995, Bowles,
1996, Tarnawski, 2004). The pressuremeter test should be performed within 15 minutes
after the borehole preparation for a quality test curve (Mair & Wood, 1987). Less
magnitude of scatter of the stress and strain readings indicates the good quality test curve
for prebored pressuremeter test (ASTM D4719).
According to (ASTM D4719), two conditions are necessary to be fulfilled for the
preparation of borehole to conduct the pre-bored pressuremeter test and to obtain good
quality prebored pressuremeter test curve:
(1) The diameter of the borehole should be according to the tolerances which are
specified for the pre-drilling of bore hole for pressuremeter test. The borehole should
meet the condition of 1.03D < DH < 1.20D, where D is the diameter of the probe and
DH is the diameter of the borehole.
(2) To stress the undisturbed strata of the wall of borehole, the equipment and the method
adopted for drilling of the borehole should cause minimum disturbance to the walls so
that the quality stress–strain curves can be achieved.
GOST (standard for pressuremeter testing) referring to 76-127 mm diameter
pressuremeter probes describes that the maximum tolerance for the diameter of the cavity
is 2mm. ISRM describes the procedure that the borehole diameter should 0.5-3mm
greater than the diameter of the PBP probe.
The tool for the drilling at site should be selected in such a way that the walls of the
resulting borehole should be smooth and the diameter, DH, of the test cavity should be as
constant as possible because if DH varies significantly along the length of the probe or if
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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25
the drilled borehole is non-cylindrical, the quality of the test will be much affected as
described in ASTM D-4719.
Verticality of the borehole is very critical and important factor before conducting the
pressuremeter test (Clarke, 1995). During hand augering, resultant borehole may not be
regular in diameter and verticality. Burst of membrane may occur in too large cavities due
to irregular drilling by hand augers. This problem is likely to arise in soft clay and loose
sand. Drilling of good borehole in soft clay and very loose sand is very difficult task
(ASTM D4719). The verticality of the boreholes can be determined by the use of
inclinometer. Inclinometer is defined as a device for monitoring deformations normal to
the axis of the pipe by means of a probe passing along the pipe (Dunnicliff. 1988). The
probe contains a gravity-sensing transducer designed to measure the inclination with
respect to the vertical. The pipe may be installed either in a borehole or in a fill, and in
most applications is installed in a nearly vertical alignment so that the inclinometer
provides data for defining subsurface horizontal deformation. Inclinometers are also
referred to as the slope indicators (Dunnicliff. 1993).
2.4.5.2 Self-boring Pressuremeters (SBP) use the self drilling technique (rotary type)
to remove the soil by rotating cutter attached at the lower end of the probe. Fig. 2.7 shows
the setup of the SBP. All the self boring systems use the similar methods for the removal
of soil. The soil cut by the rotary technique is flushed out of the hole by the use of drilling
fluid (e.g. bentonite mixed with water). The SBP probe is attached to the outer drilling
rods which are used to transmit the thrust to the probe. A hydraulic motor is used to rotate
the inner rods. These outer drilling rods are also used to take the flushing fluid to the
ground surface. Ground anchors are used to provide reaction against the friction between
the probe and the soil and to provide force for pushing the cutting shoe into the ground
during drilling. The penetration force required for the soft soils is much less than stiff
soils.
The five drilling parameters can be changed during drilling with the SBP; rate of
penetration during drilling, speed of the cutting shoe, thrust of drilling rig on the probe,
pressure of drilling fluid and the rate of flow of the drilling fluid. These drilling
parameters are to be changed with depth and type of soil strata. A good balance between
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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26
these parameters is to be maintained so that smooth drilling may be ensured with
minimum disturbance to walls of the borehole.
The SBP can drill continuously the soil to reach to the suitable location for test but
continuous drilling is not possible in rock. The cutter attached to the self boring probe
cuts the soil usually at the average speed of 50 rev / minute (Clarke, 1995). The speed of
penetration controls the size of the chippings. The speed of penetration in soft clays and
sands is one meter per 3 minutes. In stiff clays the time for one meter drilling may be one
hour because this type of soil blocks the water and reduces the speed of drilling.
The pressure capacity of the SBP probe is limited hence the strength of the soil
determines the choice of the probe. The friction on the probe depends on effective
horizontal stress and the interface friction between the soil and the probe. In case of clays,
the speed of the probe during drilling is constant and the reaction required for the
penetration increases with depth. But in case of sands, the force on the probe is increased
up to the stage of shearing of sand and the when the probe moves, the force is reduced.
During drilling with the SBP, all the particles pass through the probe. The soil particles
pass through the probe easily but the gravels cannot pass hence the drilling in gravels is
not possible. In sands the SBP is blocked due to the settling of sand out of suspension.
The SBP tests can be conducted at 1 to 2m depth interval but the borehole should be
cased to avoid the collapse of the borehole walls. The SBP is drilled until the flow of the
returning fluid starts. The SBP should be withdrawn after the test and the borehole is
advanced with rotary rig because the total borehole is not drilled with the SBP probe. The
suitable drilling depth by the SBP is 30m.
2.4.5.3 Pushed-in Pressuremeters (PIP) penetrate into the ground by the application
of force. Normally these pressuremeters are used for the ground conditions where it is
possible to push the probe into the ground. Fig. 2.8 shows setup of the PIP. Usually the
speed of penetration of PIP is 2cm/second (Clarke, 1995). The size of the cone
pressuremeter is greater than conventional cone hence larger forces are required for
penetration of PIP in soil. For the larger required forces, the reaction system is often the
limiting aspect.
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2.4.6 Pressuremeter Test Curves
There are three types of pressuremeters based on the installation methods i.e. Prebored
(PBP), pushed-in (PIP) and self bored (SBP). Prebored pressuremeters are placed in
prebored holes for testing. Pushed-in pressuremeters are inserted in the ground which
displace the soil during insertion. Self-bored pressuremeters have drilling system attached
to the probe due to which the soil is replaced and the borehole walls are least disturbed
(Clarke, 1995).
.The pressuremeter test curve can be used to derive in-situ horizontal stress, shear
strength and stiffness of soil. The geotechnical parameters derived from the test depend
upon the in-situ soil conditions, type of test and type of pressuremeter probe. The results
also depend upon the probe installation technique.
The PBP, SBP and PIP probes generate three distinct types of tests curves as shown in
Fig. 2.9. The PBP test curve is S-shaped. The first part OA is the expansion of the
membrane in the borehole before touching the borehole wall. The second part AB is the
deformation of the disturbed portion of the borehole wall. The third part BC of the test
curve shows measure of the elastic behaviour of soil. At point C, yielding of the soil
adjacent to the borehole wall starts (Clarke, 1995).
The SBP test curve has two portions, BC and CD. The applied pressure at point B shows
beginning of the expansion of the membrane and can be taken as the in-situ horizontal
stress. At point C, the ground starts yielding. From C to D, the ground shows plastic
failure.
The PIP test curve shows that the point C is yield point and from C to D the ground
shows the plastic failure.
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Fig.2.9: Typical expansion curves for the pressuremeters (a) the prebored pressuremeter
(b) the self-bored pressuremeter and (c) the pushed-in pressuremeter (after
Clarke, 1995).
Many types of pressuremeters are available now a day. These pressuremeters can be used
in a variety of soil conditions i.e. soft organic clays to hard rocks. The geotechnical
parameters which are obtained from the test curves of the pressuremeters depend upon
method of installation, testing analysis and interpretation (Clarke, 1995). To obtain good
results from pressuremeter tests, it is important to know the details of different
pressuremeter probes, installation methods and interpretation methods and the type of
ground for which these probes are suitable. Table 2.4 shows the parameters obtained from
three types of pressuremeter tests in the range of soft clay to strong rocks (Clarke, 1995).
O
B
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Table 2.4 Parameters obtained from different pressuremeter tests
Parameter Clay Sand Gravel Rock
Soft Stiff Loose Dense Weak Strong
PBP SBP PIP PBP SBP PIP PBP SBP PIP PBP SBP PIP PBP SBP PIP PBP SBP PIP PBP SBP PIP
σh A CE C A CE B C C N N N
su BE A BE BE A BE CE B N CE N N
c′ B N N N
Φ′ B B CE A CE CE A CE CE N N B N N N
Gi A A A A N N B N N N
Gur A A A A A A A A A A A A C N N A A N A N N
pl BE A BE BE A BE CE A CE CE A CE CE N N CE B N CE N N
ch B A A B A A
A, excellent; B, good; C, possible; N, not possible; E, empirical
σh, total horizontal stress; su, undrained shear strength; c′, cohesion; Φ′, angle of shearing resistance; Gi, initial shear modulus; Gur, secant shear
modulus from an unload/reload cycle; pl, limit pressure; ch, coefficient of consolidation.
(after Clarke, 1995)
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2.4.7 Calibrations
It is necessary to calibrate a PMT before and after the testing. The calibrations should be
conducted precisely and correctly so that the true response of the soil strata may be
recorded. In case of strain arm type pressuremeter, the calibrations are conducted for the
Hall Effect Transducer (HET), pressure transducer and the membrane stiffness.
2.4.7.1 Calibration of Displacement Transducer is applied on the displacement
readings of the membrane from the outer surface of the pressuremeter probe. The
sensitivity of the displacement transducer changes with the change in the length of the
cable if the voltage is used for the signals. The displacement transducer is calibrated with
the help of micrometer. One strain arm is fixed and the other is opened up to the full
range. The probe is connected to the control system. The readings in mV (millivolt) are
recorded for each 3 to 5% or 1mm opening of the strain arm. During testing in the field,
the readings of the displacement of the membrane in mV are converted to % expansion of
the membrane. The readings are taken up to the full range of the expected expansion of
the membrane and then the decrements down to zero in same interval of 1mm are also
recorded. The sensitivity is recorded as mV/mm and the ratio of change in displacement
with the outer diameter of the pressuremeter probe is termed as cavity strain.
2.4.7.2 Calibration of Pressure Transducer is applied on the pressure readings recorded
during the pressuremeter test. The pressure transducer show the change in pressure which
is measured in mV. The pressure transducer is operated with the same power supply
which is used for the displacement transducer. The pressure transducer is fitted on the
Budenberg dead weight tester. The static pressure is applied on the tester. The reading of
the pressure measured by the pressuremeter is noted in mV.
2.4.7.3 Calibration of Membrane for Stiffness is conducted so that the net cavity
pressure applied on the soil may be determined. The membrane is installed on the probe
and the probe is attached with control unit. The membrane is expanded and the readings
for the pressure and displacement of the membrane from the surface of the probe are
recorded. The pressure-displacement data are plotted and the resultant equation of this
pressure-displacement data is applied for the correction of the displacement in tests.
Membrane stiffness is not much important in strong ground conditions but it is very
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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31
critical in soft ground conditions where the strength of soil is very low and the membrane
correction becomes very significant.
2.4.8 Prebored Pressuremeter Test Procedure
ASTM D-4719 provides standard procedure for the prebored pressuremeter test. The
pressuremeter test is of two types i.e. stress controlled and strain controlled. The borehole
is prepared by any method recommended by ASTM-4719 (2000). The time between the
preparation of the borehole and performance of the test should be standardized so that the
repeatable disturbance can be achieved at the whole site. The control unit and the pressure
system are attached with probe and the probe is lowered in the borehole. The test is
started immediately so that less time may be allowed to the walls of the borehole to relax.
After the installation of the probe in the borehole, the membrane of the pressuremeter is
expanded enough to test the undisturbed soil around the probe. The membrane is
expanded by increasing the pressure. Software can be used to record the pressure-
displacement readings. When the membrane is expanded sufficiently, it is then unloaded
and the initial portion of this unloading is considered elastic for certain range of stress.
The test is terminated at the three conditions i.e. maximum displacement capacity of the
membrane, maximum pressure capacity of the system and the burst membrane. The burst
membrane can happen during the test due to soft layer of the strata, loose clamping of the
membrane on the probe surface or much greater diameter of the borehole than the probe
diameter. The readings of the pressure and displacement are recorded usually in mV and
then converted to the engineering units. The pressure is applied in increments. The
pressure at each increment is maintained constant for 60 seconds. The unload-reload
loops are also conducted for the determination of shear moduli of soil being tested. The
corrections for pressure, displacement and the membrane stiffness are applied to the
recorded data and the pressure versus cavity strain curve is plotted for the interpretation
of shear modulus, shear strength, in-situ horizontal stress and limit pressure.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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2.5 SHEAR MODULUS
The stiffness of soil is an important parameter for the prediction of deformation of soil
strata. The shear modulus is defined as the ratio of shear stress to shear strain.
2.5.1 Shear Modulus from Pressuremeter
The determination of shear modulus (soil stiffness) is the most important task in
pressuremeter testing as the shear modulus (G) is very important parameter in
geotechnical designs. For the determination of G, the small unload–reload loops can be
conducted in the elastic range as proposed by Wroth (1982). Different types of moduli are
determined from pressuremeter test.
Fig. 2.10 The unload-reload loop showing the lines to calculate the Gu, Gr and Gur.
It is evident from Fig. 2.10 that the value of shear modulus depends upon the strain range
hence the shear modulus should be given with strain and stress amplitudes and the stress
and strain values at which the modulus was measured. The Gur can be calculated from the
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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slope of the line joining the apices of the loop. Upper apex of the loop shows the
maximum stress and strain values for the determination of unload secant modulus Gu and
the lower apex of the loop shows the minimum stress and strain values for the calculation
of reload secant modulus Gr. The Gu, Gr and Gur are not the shear moduli of an element
of the tested soil but show the average stiffness response of the soil around the probe. For
radial displacement type PBP probes, the Gur = ½(Δp/Δєc) where Δp and Δєc are the
difference of pressure and cavity strain between the two apices of the loop of PMT curve.
Fig. 2.11 The elastic limit of clays on unloading for pressuremeter test curve (after Wroth,
1982).
In Fig. 2.11 the portion AB of the PMT test curve of clay soil shows that the soil fails at
point B, the membrane is further expanded up to point C at which the soil is unloaded.
This unloading is elastic until the soil fails in extension at point D. The soil is reloaded at
point D and the curve rejoins the previous trend at point E. The elastic limit of unloading
in clayey soils is 2Su (the unconfined compressive strength of the ground) and beyond this
limit the soil will fail in shear. After failure in the clayey soil, the test remains undrained
and the effective stress is not changed hence the Gu values in this case remain same if the
stress and strain amplitudes remain unchanged.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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Fig. 2.12 Elastic limit of sands on unloading of the pressuremeter test curve (after Wroth,
1982)
The limit for the elastic range in the unloading portion of the unload-reload loop of PMT
test curve in sand is shown in Fig. 2.12. The elastic range of behaviour of sands is
[2sin′sin′p′beyond which the sands fail in extension. The p′ is the effective
stress. The pressuremeter tests in sands are drained so the effective stress increases as the
cavity strain increases resulting in the increase of Gur. As the angle of internal friction
(′of sands is usually unknown at the time of pressuremeter testing at site hence the
estimated value of ′i.e. 350 is taken for the assessment of unloading in pressuremeter
tests in sands. Using this angle, unloading amplitude of pressure comes to be 0.72 (p - uo)
max where (p - uo) is the effective stress. Fahey (1992) suggested that the amplitude of
pressure should be taken equal to half of this value so that the hysteresis of the loop may
be reduced.
2.5.2 Non-linear Stiffness Profile
It was proposed by Reid et al. (1982) that the stress and strain range should be specified
for G determined from the PMT. For precise determination of G from the PMT, strain
elastic theory should be applied to unload-reload loop (Schnaid, 1990).
The unload-reload loop in pressuremeter test always shows some extent of hysteresis
even if the loop is conducted in the elastic limit of any soil (Clarke, 1995). Unload and
reload secant shear moduli are normalized by the effective pressure at which the soil was
(2 sin ′) p′
1 + sin ′
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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35
unloaded. The Poisson's ratio used in Menard pressuremeter (MPM) tests is 0.33 (Clarke,
1995).
Fig. 2.13 shows that the relationship of the reciprocal of the stiffness (Euo and Ero moduli
of elasticity from unload and reload portions respectively of the loop) and strain is a
straight line, hence the stiffness can also be shown as hyperbolic function of strain
(Briaud et al., 1983a).
Fig. 2.13 Variation of secant moduli with strain from unload-reload loops of PMT (after
Briaud et al., 1983a)
2.5.3 Degradation of Shear Moduli
In pressuremeter testing, the secant shear moduli (unload and reload) decrease with
increase in strain. Fig. 2.14 shows that unload and reload moduli from PMT decrease with
increase in strain. The shear moduli degradation curves are very useful in geotechnical
design as the shear moduli at different strain levels can be assessed. Instead of
determining single value of shear modulus (Gur) from the unload-reload loop of the
pressuremeter test, the secant moduli (unload and reload) can be determined from the
PMT loop for the corresponding strains. These moduli can be used in geotechnical
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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36
designs where specific strains are very important to be considered for the selection of
shear moduli.
The shear modulus from the unload-reload loop of the pressuremeter is almost
independent of the initial disturbance due to the installation of the pressuremeter probe
(Hughes, 1982; Wroth, 1982; Powell and Uglow, 1985; Houlsby and Withers, 1988;
Lacasse et al. 1990; Powell, 1990).
Fig. 2.14 The variation of secant shear modulus with strain for PMT in London clay
(after Clarke, 1993)
Figure 2.14 shows variation of secant shear modulus normalized with effective horizontal
stress versus current cavity strain for the PMT tests in London clay. After the yield point
during pressuremeter test, the change in mean effective stress is minor in clayey strata
(Wroth, 1982). Hence in clay, the shear modulus is independent of the strain level at
which the unload-reload loop was conducted (Clarke, 1995).
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The current cavity strain, ourr, is calculated by using the values of maximum cavity strain
for the unloading portion of the loop and the minimum cavity strain for the reloading
portion of the loop.
um
umo
1ourr 2.1
The reloading stiffness response is independent of the stress and strain levels at which it
is determined during the pressuremeter test but the unloading stiffness is different from
loop to loop and also from the reloading stiffness even measured in the same loop of the
PMT test curve. The variation of unloading stiffness may be due to consolidation taking
place during unloading. Clarke (1993) described that the reloading curve gives more
consistent results of stiffness than unloading curve. The significance of the unload-reload
loop for the evaluation of non-linear stiffness profile was recognized by Muir-Wood
(1990).
2.6 MEASUREMENT OF IN-SITU HORIZONTAL STRESS (h)
The in-situ horizontal stress is the horizontal stress of soil on the membrane of the
pressuremeter when the soil around the probe is at its natural position.
The point ao is the reference datum for PBP, SBP and PIP test curves (Fig. 2.15) at which
the stress acting on the probe membrane is in-situ horizontal stress (σh). The SBP is the
ideal test to determine σh correctly. When the SBP probe is installed in the ground, the
diameter of the cavity is equal to the outer diameter of the probe. The membrane is in
contact with the walls of the pocket, hence if the membrane is expanded, it lifts off from
the probe and this lift off pressure is equal to σh. It is not possible to directly determine σh
from PIP test curves as the pressure of the soil on the membrane exceeds σh during the
installation of the membrane.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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Fig. 2.15 The reference datum on PIP, SBP and PBP test curves.
The diameter of the borehole at the in-situ horizontal stress is taken as the reference
datum. The interpretation of the PMT curve depends on the reference datum. In Fig. 2.16,
a PBP test curve is shown. It is difficult to determine datum from PBP curve. The
pressure inside the membrane is increased and at point A, it becomes equal to the
membrane stiffness plus pressure of mud. Further by increasing the pressure, the
curvature of the curve changes at point B where rate of increase of pressure is more. If the
membrane is expanded further up to point C to compress the softened material of the
pocket walls, the slope of the curve becomes linear. At point C, the membrane is in touch
with pocket walls and the pressure at this point is po, which is not equal to σh as the pocket
walls were unloaded after drilling. By increasing the pressure up to the point D, the datum
point ao is reached where the pocket walls have attained the natural position, as was
before drilling. At point D, the pressure is equal to σh.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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Fig.2.16 A typical PBP curve showing reference datum and insitu horizontal stress.
Following are some methods for the determination of σh. These methods are applicable to
the use of different probes.
(1) the lift-off method
(2) methods based on shear strength
(3) methods based on test procedure
(4) fitting functions to the test curve
(5) empirical correlations with other data
The lift-off method and the method based on shear strength are described here. The detail
of other methods is given in Clarke (1995).
2.6.1 Lift-off method
For the correct in-situ measurement of the horizontal stress, the SBP was developed. The
lift-off pressure method is applicable to all self boring radial or volume displacement type
probes in which the membrane is supported by the body of the pressuremeter probe at the
beginning of the test. When the membrane lifts-off from the probe surface, the pressure is
equal to σh. For the determination of σh, the initial portion of the test curve is considered
i.e. 0 to 0.5% cavity strain.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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The membrane lifts-off at the pressure equal to its stiffness. The membrane deviates
clearly from the initial stress-strain trend at the lift-off pressure. The calibration of the
membrane for stiffness is conducted to find out the lift-off pressure in air. Clarke (1993)
described that disturbance of the walls of borehole up to 0.5% cavity strain is observed
even by the use of SBP. Newman (1991) proposed that the good quality PMT in sands
can be conducted for the determination of σh when the disturbance of the borehole walls is
less than 0.2%.
The shapes of the self boring pressuremeter test curves are shown in Fig. 2.17 which
shows that there may also be some disturbance to the walls of the borehole during drilling
by the SBP which may cause deviation of the test curves from the ideal shape. The causes
for these deviations are under drilling, over drilling and the moving axis of the probe as
shown in Fig. 2.17. The ideal curve for the SBP is also shown in Fig. 2.17 and it can be
concluded by keeping in view the shapes of the curves that during the PBP test the
disturbance to the walls of the borehole causes the inability to directly measure the in-situ
horizontal stress as the shape of test curve similar to the SBP cannot be achieved by
traditional drilling mode for the direct determination of the in-situ horizontal stress. The
traditional drilling modes, for the prebored pressuremeter testing, cause the soil to relax
after the drilling tool is withdrawn from the borehole.
Fig. 2.17 Shapes of initial portion of the SBP curves due to drilling techniques.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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2.6.2 Method based on Shear Strength
Denby (1978) and Fahey and Randolph (1984) have described a method for the
determination of in-situ horizontal stress in clayey soils and sands. According to this
method, in-situ horizontal stress for the cohesive and cohesionless soils can be
determined by following steps.
a) Several reference data for the pressuremeter test curve are selected.
b) The strains of the PMT test curve are corrected for each reference datum strain (RDS)
c) The applied pressure versus ln (cavity strain) is plotted for the clayey soils for
different reference datum points.
d) The ln (applied pressure) versus ln (cavity strain) is plotted for the cohesionless soils
for different reference points.
e) The reference datum for which longest straight line (as shown in Fig. 2.18) is obtained
will represent the initial cavity diameter against which the in-situ horizontal stress can
be determined from PMT curve for clayey as well as cohesionless soils.
f) The pressure against the chosen initial diameter of the cavity, are determined from the
pressuremeter curve. This pressure is taken as in-situ horizontal stress.
Fig.2.18 Pressuremeter curves based on different reference datum points.
Reference datum
of this line is used
to obtain ho
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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2.7 DETERMINATION OF SHEAR STRENGTH OF SOIL
Determination of shear modulus and horizontal stress is independent from the drainage
conditions but the shear strength determination depends upon the drainage conditions
during PMT test (Clarke, 1995).
It is more common to find out the shear strength from the PBP test curve using empirical
methods (Table 2.5).
Table 2.5 Empirical relations between undrained shear strength and net limit
pressure for different soils (after Clarke, 1995)
Undrained Shear strength
(Su)
Clay type References
(Plm - h) / k K=2 to 5 Menard (1957d)
(Plm - h) / 5.5 Soft to firm clays
Amar and Jezequel (1972) (Plm - h) / 8 Stiff to very stiff clays
(Plm - h) /15 Firm to stiff clays
(Plm - h) /6.8 Stiff clays
Marsland and Randolph
(1977)
(Plm - h) / 5.1 All clays
Lukas and LeClerc de
Bussy (1976)
(Plm - h) / 10 + 25 Amar and Jezequel (1972)
(Plm - h) / 10 Stiff clays Martin and Drahos (1986)
Plm / 10 + 25 Soft and stiff clay Johnson (1986)
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A test curve of self boring pressuremeter is shown in Fig. 2.19. The pressure is plotted
against ln (cavity strain) for the loading curve data and it is obvious that the resultant plot
produces a best fit straight line. The slope of this straight line is equal to undrained shear
strength (Su). The data for plotting should be taken after 3.5% strain due to probe
installation disturbance. This method can also be used for the prebored pressuremeter
testing if sufficient expansion of the pressuremeter membrane is achieved. Also for the
application of this method to the PBP, suitable reference datum is also required for
determination of precise value of Su.
Fig. 2.19 Determination of Su from SBP pressuremeter test in clay (after Clarke, 1995).
2.8 DETERMINATION OF LIMIT PRESSURE (PL)
Limit pressure defined as “the maximum pressure reached during a pressuremeter test at
which the cavity will continue to expand indefinitely” is very useful parameter to estimate
strength and stiffness of soils. In reality, indefinite expansion of membrane is not possible
as the expansion measurement is restricted. However, its value can be estimated by
extrapolating the pressuremeter curve to infinity.
Menard described that the pressure required to double the initial volume of the cavity for
MPM (Menard Pressuremeter) during the test is called as limit pressure (PL). Double of
the initial volume of the cavity is equivalent to 41% strain (Clarke, 1995). The limit
pressure depends upon the extent of disturbance during the drilling process, the
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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44
installation technique and the properties of ground strata. A typical BPB curve is shown
in Fig. 2.20 in which limit pressure is shown at 41% cavity strain.
0
200
400
600
800
1000
1200
0 5 10 15 20 25 30 35 40 45
Cavity strain, %
Ca
vity p
ressu
re,
kP
a
Fig. 2.20 A typical PBP curve showing the limit pressure.
2.9 LABORATORY TESTING
Following laboratory tests are commonly conducted for the geotechnical characterization
of soils in the laboratory.
2.9.1 Soil Classification Tests
For the grain size distribution of the soil, sieve analysis and hydrometer analysis are
conducted. Sieve analysis is performed for the grain size determination of gravel and
sand. For the silt and clay soils, the hydrometer test is performed for obtaining gradation
curve.
Liquid and plastic limit (Atterberg‟s limits) tests are performed for the evaluation of the
plasticity index of cohesive soil. The plasticity index, determined from liquid and plastic
limits, can be used in correlations related to the strength properties of soil (Bowles, 1996).
Assessment of consolidation depends on the liquid limit. Unified Soil Classification
System is usually used for classification of soil on the basis of particle size distribution,
liquid limit and plastic limit results.
Limit pressure at 41% cavity strain = 1066 kPa
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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2.9.2 Strength Tests
Shear strength is the resistance of soil mass against deformation. This resistance is
developed by rolling, sliding and crushing of soil particles during the process of
deformation (Bowles, 1996). The shear strength is measured by interparticle cohesion “c”
and resistance against the slip between the soil particles called as angle of internal friction
“”. The effect of resistance of soil particles to rolling and grain crushing is also covered
by “c” and “”.
Triaxial compression test can be used for the determination of modulus of elasticity (E).
The direct shear test can be used to determine angle of internal friction (′ of non-
cohesive soils and unconfined compression test can be used for the determination of
undrained shear strength (su) of cohesive soils.
2.9.2.1 Isotropically Consolidated Undrained (CIU) triaxial test is a strength test
which is conducted on cohesive soils (ASTM D-4767). Careful triaxial sample
preparation method is vital for the quality triaxial test and results. The tubes are cut in
small pieces by hand using hacksaw. The samples are extruded as soon as possible to
conduct the triaxial test so that the soil disturbance at the periphery of the tube may be
avoided. The undisturbed sample extruded from the tube is in cylindrical shape. The
sample is then transferred in the split mould in which the membrane is already stretched
by applying the negative pressure (vacuum) of about 15 kPa. The sample along with split
mould is installed on the lower platen of the triaxial cell, the membrane is stretched on the
lower platen and the O-rings are fixed on the membrane. When the upper platen comes in
contact with the upper end of the mould, the membrane is stretched on the upper platen
and the O-rings are fixed on the membrane. The split mould is untied in two portions and
removed from the cell. The cell (made of Perspex) is assembled and about 3/4th
of the cell
is filled with water on which the cell pressure is applied. The sample is saturated at least
upto B = 0.98. Then the sample is consolidated by applying the effective consolidation
pressure with the drainage lines open. After the drainage is complete and all the pore
water pressure developed by applying the consolidation pressure is dissipated, the sample
is ready for the shear stage. The rate of shearing in clay and sand is different. Very slow
rate of shearing is applied in case of clays so that the changes in pore water pressure
developed during the shear stage may be noted precisely as in clays the significant time is
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
46
required for the pore water to travel from sample to the pore pressure transducer. The all
around pressure in the triaxial cell is maintained constant i.e. isotropic condition during
the test. The speed of shearing can be assessed from the time required for the
consolidation of the test. The shear strength parameters “c” and “” are determined from
this test.
2.9.2.2 Isotropically Consolidated Drained (CID) Triaxial Test is a strength test
conducted on cohesionless soils. Drained shear strength parameter ′ is evaluated from
this test. The saturation and consolidation stages are same as in CIU triaxial test. The only
difference is that the drainage lines are open during shear stage so that the pore water
pressure developed during the shear stage may be dissipated simultaneously.
2.9.2.3 Stiffness of Soil from CIU and CID Triaxial Test can be determined by
performing unload-reload loops during triaxial tests as shown in Fig. 2.21. Unload-reload
modulus (Eur) of soil can be determined by conducting the unload-reload loops in triaxial
compression tests (Duncan & Chang, 1970). Modulus obtained from unload-reload loop
is proportional to the effective confining stress in triaxial test (Duncan & Chang, 1970).
The value of Eur is affected by the change of deviator stress in unload-reload loop in
triaxial test (Makhlouf & Stewart, 1965). The deformation during unload-reload loop of
triaxial test in sand can be approximately considered as elastic (Holubec, 1968; Duncan
and Chang, 1970; Coon and Evans, 1971; Lade and Duncan, 1975). A criterion has been
described by Lade and Duncan (1976) for the modes i.e. primary loading, unloading and
reloading in triaxial compression testing.
The unload-reload cycles in the triaxial test are static as the frequency of unload-reload
cycles does not fall in the frequency range of 1/6 to 10 Hz described by Bowles (1996)
which is required to generate dynamic moduli. Fig. 2.22 shows static triaxial test with
unload-reload loops.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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47
Fig. 2.21 Stress-strain curve q vs. in monotonic triaxial test with unload-reload loop
Fig. 2.21 shows that as the deviator stress increases, the axial strain also increases. An
unload-reload loop is shown in the loading curve. The unload and reload portions of the
loop have been shown with downward and upward arrows respectively. The upper apex
of the loop is the point of intersection of the unload and reload curve. The lower apex of
the loop is the point of minimum deviator stress. The unload-reload modulus of elasticity
(Eur) is determined from the slope of the line between these apices. Fig. 2.21 shows that
the reload curve again attains the trend of loading curve showing that if the unload-reload
loop is conducted in elastic limits, then the loading trend of the curve is not affected. This
type of unload-reload loops can be conducted more than once in the same loading curve
for the evaluation of effect of stress and strain amplitude on the unload-reload modulus as
the variation in strain and stress amplitude changes the Eur value.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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48
Fig. 2.22 Unloading-reloading modulus of soil in triaxial compression test (after
Duncan and Chang, 1970)
The unload-reload modulus of elasticity increases with increase in effective stress
(Duncan and Chang, 1970). During the primary loading in triaxial test, the deformation is
not affected by the previous unload-reload cycles conducted on the lower stress level than
the present stress level (Makhlouf & Stewart, 1965). The shear strength or the angle of
internal friction is not affected by the stress history of the sand deposit from which the
sample has been taken for the triaxial test (Lade and Duncan, 1976).
2.9.2.4 Comparison of Stiffness from PMT and Triaxial Tests is very important as
both tests are static. Pressuremeter test is a field test and triaxial test is a laboratory test
which is time consuming. The significance of unload-reload cycle for the non-linear
stiffness profile was described by Muir-Wood (1990). Jardine (1991) compared the PMT
results with KoTC and UU triaxial tests for the Cannons Park site London (Fig. 2.23)
based on the PMT data of the unloading curves. The pressuremeter results lie below
triaxial as shown in Fig. 2.23 but this can be due to difference of initial stress, stress rate
and strain rate in PMT and triaxial tests. Fig. 2.23 shows the infinite stiffness and
maximum stiffness is difficult to be assessed from these curves.
3820 kg/cm2
0.6
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
49
If the shear modulus from pressuremeter and the triaxial (TXL) test are determined, the
shear moduli values are comparable. It can also be observed that pressuremeter results lie
below triaxial tests in graphs of shear moduli from PMT and TXL (Jardine, 1991).
According to Muir & Wood (1990) the shear modulus values from pressuremeter and
triaxial test were not comparable. Jardine (1992) developed a transformed strain approach
to calculate the shear moduli in pressuremeter tests to compare with the shear moduli
determined from triaxial tests.
Muir & Wood (1990) proposed that the modulus and the non-linear stiffness profile can
be determined from the unload-reload loops. Shear modulus degradation characteristics of
soils have been evaluated in triaxial tests by Jovicic and Coop (1997), Yamashita et al
(2000), Wang and Ng (2005) and in pressuremeter tests at in situ conditions by Wood
(1990), Jardine (1991, 1992), Ferreira (1992), Robertson and Ferreira (1993), Ng and
Wang (2001), O‟ Rourke McGinn (2006). Non-linear shear modulus degradation
characteristics can be used in geotechnical problems which include deformations of the
ground during earthquakes and deep excavation in clay (Yu Wang & Thomas D.
O‟Rourke, 2007). Unloading stiffness varies between different cycles and it is also
different from reloading stiffness of an unload-reload cycle in pressuremeter test (Clarke,
1995). In the pressuremeter tests conducted in clay the reloading stiffness is more
consistent (Clarke, 1993).
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
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50
Fig. 2.23 Comparison of secant moduli determined from pressuremeter and triaxial (after
Jardine, 1991)
2.9.2.5 Comparison of static and dynamic stiffness is very important for the
geotechnical designs. During cyclic loading, the secant stiffness determined from the
stress-strain curve is called dynamic stiffness. The static stiffness is determined from the
first stress-strain curve of triaxial test. The difference between the static and dynamic
moduli is the magnitude of strain at which these moduli are measured. The dynamic and
static moduli are determined at very small and large strain amplitudes respectively
(Wichtmann and Triantafyllidis, 2009).
The small strain stiffness is very important for designing the foundations which are
subjected to the vibratory loads such as machine foundations (Wichtmann and
Triantafyllidis, 2009).
The dynamic shear modulus values determined from the resonant column tests are 1.75
times higher than static shear modulus determined from pressuremeter tests. The shear
stiffness measured in the resonant column test is underestimated because the in-situ stress
conditions and the fabric can not be truly adopted in the laboratory.
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
51
The modulus (Es or G′) is called as “dynamic modulus” when cycles are performed at low
amplitude and the frequency range is 1/6 to 10 Hz.
2.9.2.6 Resonant Column Testing is most commonly conducted to determine the
dynamic shear modulus (Gmax) at low shear strains. The dynamically derived parameters
are very important in geotechnical designs. An important parameter Gmax is used in
variety of geotechnical applications. Gmax has a significant role in solution of small strain
(< 10-3
%) problems relating to effects of earthquake, wind loading, traffic vibrations and
machine vibrations (Bates, 1989).
In resonant column test the G is determined by the application of torsional vibrations.
The specimen is installed in a pressure cell between the two platens which hold the
specimen. One is the passive-end platen which is fixed and the other is active-end platen.
The sine wave generator, which is an electric instrument, is the part of resonant column
apparatus for producing sinusoidal current with the facility to adjust the frequency. The
sinusoidal excitation device (the electromagnet system) is attached to the active-end
platen where the specimen is vibrated at certain frequency of excitation and amplitude.
The vibration excitation is torsional. The transducers are used to measure the vibration
amplitude at the active end platen. The mass and the rotational inertia of the active end
platen along with the parts of the electromagnet system which are in motion with it are
already known before the test is conducted. The G values determined from resonant
column test depend upon the strain amplitude of vibration, void ratio of soil sample and
the applied effective stress (ASTM D-4015). For torsional motion, the shear strain is an
average value for the entire diameter of the specimen. The shear strain value is zero at the
axis of rotation of the specimen installed in resonant column device. The shear strain
value increases from axis of rotation to a maximum value at the perimeter of the
specimen, hence the average value of shear strain ( is taken and used in calculations.
The average can be taken at the radius equal to 80% of the radius of the cross section of
the specimen.
The undisturbed sample tube is cut into pieces according to the length of the specimen
required. The specimen is extruded from the cut piece of the sample tube by the use of
extruder. The specimen is taken in the mould in which membrane is already fixed. The
specimen is placed in the pressure cell. The end platens are attached to the specimen with
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
52
special care so that the sample disturbance may be minimized and also particular care is
necessary for the attachment of vibration excitation device to the active end platen. The
cell is attached with the saturation and pressure panel. For the application of isotropic
stress to the specimen, the liquid media is used in pressure cell. The specimen is
saturated by introducing the water from one end of the sample. After saturation stage, the
sample is consolidated at the certain effective stress (e.g. 100 kPa). The applied frequency
is adjusted so that the resonance condition is achieved at the stage where the sinusoidal
excitation force in phase with the velocity of the active end platen attached to the upper
end of the specimen. The amplitude is increased with increase in voltage and the reading
of amplitude is noted from the voltmeter. At resonance condition, the frequency and the
amplitude are used to determine shear modulus, G. The sample is again consolidated at
higher effective stress (e.g. 200 kPa). The frequency is increased from the previous stage
and the resonance condition is created again for the certain frequency and amplitude of
vibration. Commonly the frequency and amplitude of vibration for the four stages of
effective stress (i.e. 100 kPa, 200 kPa, 300 kPa and 400 kPa) are determined. The shear
modulus, G, determined from resonant column test depends upon the amplitude of strain,
effective stress and void ratio of the soil specimens being tested (ASTM D-4015).
2.9.2.7 Unconfined Compression Test (UCT) and Direct Shear Tests are performed
for the determination of su and ′ respectively. Unconfined compression test is conducted
on cohesive soils to determine the unconfined compressive strength (qu). Undrained shear
strength (su) can be calculated as su = qu /2. Direct shear test is performed on
cohesionless soils to determine the angle of internal friction “′”. The shear strength ()
determined from the direct shear test is = tan′ where is the normal stress applied
during the test.
2.9.2.8 Correlations Developed by other Researchers between pressuremeter,
laboratory testing and standard penetration testing are as follows:
Yagiz et al. (2008) developed correlation between limit pressure (pL) and SPT blows
(Ncor) for medium to very stiff sandy silty clay.
7.21945.29 corL Np 2.3
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
53
Tschebotarioff (1973) developed correlation between undrained shear strength (su) and
SPT blows (Ncor) for very soft to stiff clays.
coru Ns 86.7 2.4
where su is in kPa.
Wieringen (1982) developed correlation between cone tip resistance (qc) and limit
pressure (pL) for clays where qc and pL are in kPa.
Lpqc 3 2.5
Rehman (2010) developed correlation between cone tip resistance (qc) and limit pressure
(pL) for soft to very stiff clays
Lc pq 5.8 2.6
where qc (cone tip resistance) and pL are in units of kPa.
Amar and Jezequel (1972) developed correlation between undrained shear strength (Su),
limit pressure (pL) and in-situ horizontal stress ( ho ).
hoLu ps 1818.0 2.7
where all parameters are in units of kPa.
2.10 SUMMARY
Geotechnical characterization of soils is conducted by in-situ and laboratory testing. The
common in-situ tests include pressuremeter test, CPT and SPT. The frequently conducted
laboratory tests include triaxial, direct shear, unconfined compression and classification
tests. The sophisticated laboratory tests like resonant column and unload-reload triaxial
tests on alluvial soils are conducted for the determination of stiffness of soil.
There are two steps of soil characterization; drilling and soil testing (in-situ and
laboratory). Three types of pressuremeters; prebored pressuremeters (PBP), self boring
pressuremeters (SBP) and pushed-in pressuremeters (PIP) are used worldwide for the
determination of strength, stiffness and in-situ horizontal stress of the soil. Self boring
pressuremeters are most suitable for the determination of in-situ horizontal stress. The
CHAPTER-2 GEOTECHNICAL CHARACTERIZATION OF
ALLUVIAL SOILS
54
pressuremeter mainly consists of probe, control system and control cable with pressure
supply system. The pressuremeter is very suitable for soil characterization as compared
with other in-situ tests.
The two conditions for the drilling of boreholes for pressuremeter testing are very
important i.e verticality of boreholes and constant diameter of borehole. The shear
modulus (G) is most important geotechnical parameter which is determined from
pressuremeter testing. The unload, reload and unload-reload shear modulus can be
determined from the unload-reload loops of the pressuremeter test curves.
The shear modulus of soil determined from pressuremeter tests and laboratory testing can
be compared. The dynamic shear modulus of soil can be determined from resonant
column test.
CHAPTER-3
55
DEVELOPMENT OF DRILLING SYSTEM, IN-SITU TESTING AND
LABORATORY TESTING
3.1 INTRODUCTION
The geotechnical characterization of alluvial soils comprises in-situ and laboratory
testing. The first and most important step for the quality in-situ testing is high quality
drilling of boreholes. For this purpose, a mechanical drilling system (MDS) for vertical
and constant diameter boreholes has been developed. This chapter presents salient
features of the MDS and drilling of boreholes with MDS. Pressuremeter tests were
conducted in the boreholes drilled by Hand Auger (HA), Rotary Rig (RR) and MDS for
the comparison of quality of pressuremeter test curves.
During this research, in-situ testing has also been performed using pressuremeter, CPT
and SPT for the determination of geotechnical properties of soils at field conditions. The
field stress conditions have been simulated in the laboratory to compare the results of
field and laboratory testing. Financial impact of each drilling system along with the
quality of test curves has also been included in this chapter.
3.2 DEVELOPMENT OF MECHANICAL DRILLING SYSTEM (MDS)
The drilling systems recommended by ASTM D4719 for the drilling of boreholes for
pressuremeter testing include common methods like hand auger and rotary drilling rig.
The rotary rig and hand auger have limitation for the vertical and constant diameter
borehole. Hence there was a need to develop a drilling system for achieving the vertical
and constant diameter borehole with cost effectiveness. A mechanical drilling system was
developed for this purpose.
3.2.1 Salient Features of Mechanical Drilling System (MDS)
Main features for the development of mechanical drilling system (MDS), considered
necessary, were the verticality and constant diameter during drilling so that testing quality
with pressuremeter could be enhanced. Fig. 3.1 shows a pictorial view of the drilling
system developed.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
56
The MDS was developed on the basis of operation of rotary drilling rig. The base plate
and the rods (fixed in jaws) are at right angle to each other. A wheel applies the torque
manually resulting in the rotation of the rods which are attached in the jaws assembly.
The upper end of the hollow pipe is attached with static weight pan and the lower end is
attached to the jaws assembly.
A gear assembly has been incorporated to increase the output of the applied force. Two
guiding rods ensure the vertical movement of the hollow pipe and eliminate the effect of
eccentric loading of the static weights placed in the pan. The head contains two toothed
rings. One is attached with the shaft of gear assembly and the other is attached with the
hollow pipe. Hence the applied force from the wheel is transferred to the hollow pipe for
the rotation of drill rod.
Fig. 3.1: Mechanical drilling system (MDS)
The jaws assembly provides the facility to fix the drill rods in position. The sliding
assembly has been attached with the base plate of the system to incorporate the sliding
Jaws assembly
for fixing rods
Slotted sampler
Sliding
assembly
Wheel for
torque
Pan for static
weights
Static weights Leg of tripod
Base plate
Drill rod
Guiding rod
Leveler
Gear assembly
Anchor
points
Hollow pipe
Head
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
57
facility for to and fro motion of the system for attachment and removal of the samplers
from rods before and after drilling respectively. The sliding assembly provides facility to
remove the sample from the sampler easily and protects the sample from falling into the
borehole.
A static weight pan is a special feature of this system. The static weights are placed on the
pan to increase the penetration force during drilling in stiff clay or dense sand. It is
necessary to place the weights uniformly on the pan to avoid eccentricity. The rods are
added or removed by pulling up with the conventional rope and pulley system attached
with the light weight tripod.
Slotted and helical type samplers were fabricated to drill the boreholes of 48.2 mm
diameter. The attachment of these samplers with the MDS is shown in Figs. 3.2 and 3.3
respectively. The diameter of the samplers was selected such that the diameter of the
drilled borehole is slightly greater than the diameter of the pressuremeter probe
(Tarnawski, 2004).
3.2.2 Drilling with the MDS
For drilling, the MDS was placed at the test location such that the centre of jaws assembly
was exactly above the borehole location. The MDS was leveled at site by placing the
leveler on the base plate for horizontal leveling which resulted in the vertical leveling of
hollow pipe. The drill rod of 1m length was inserted from the hole in the static weight pan
into the hollow pipe. Sampler was attached at the lower end of the drill rod. Sampler
attached with the drill rod was put on the borehole location and the drill rod was tightened
in the jaws assembly.
Torque was applied through the wheel in clockwise direction to rotate the drill rod.
Suitable static weights were placed on the weight pan to increase the rate of penetration
of sampler.
Refusal in penetration during drilling showed the filling of the sampler with soil. The rods
along with sampler were pulled up by the rope and pulley system attached with the tripod.
When the sampler containing soil sample reached the ground surface, the MDS was
moved back manually in the horizontal direction by sliding assembly. The sampler was
removed from the drill rod and the sample was taken out from it. The sampler was again
fixed with drill rod for further drilling. In this way, each borehole was drilled up to 10m
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
58
depth. A pictorial view of the borehole drilled by the MDS is shown in Figs.3.4 & 3.5.
Constant diameter and smooth surface of the borehole is evident from the pictures.
Fig. 3.2 Slotted type sampler.
Fig. 3.3 Helical type sampler.
Slotted type
sampler Precise
diameter
borehole
Jaws assembly
Drill rod
Soil sample
Tripod
Helical
sampler
with soil
sample
Precise
diameter
borehole
Pre-bored
pressuremeter
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
59
Fig. 3.4 Regular diameter and smooth surface borehole drilled by MDS
Fig. 3.5 Longitudinal section of borehole
Borehole
Smooth
surface of
borehole
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
60
3.3 DRILLING WITH HAND AUGER
The hand auger is recommended in ASTM D-4719 for the drilling of boreholes for the
PMT. The hand auger was used for the drilling of boreholes according to the procedure
described in ASTM D-1452. Iwan type auger (tubular type hand auger), as recommended
in ASTM D-4719, was used for drilling. The hand auger was attached with rod and
handle for the rotation of the auger. The borehole was drilled by rotating the hand auger
with the downward pushing force manually. The disturbed sample was recovered by the
rotating action of the auger. The samples were labeled and preserved in plastic jars for the
specific depths from where the samples were required for the laboratory testing. The
additional rods were attached as the depth of borehole increased.
3.4 DRILLING WITH ROTARY RIG
Drilling of boreholes by RR was carried out for the pressuremeter testing as
recommended in ASTM D-4719. For drilling with RR, a rig attached with specially
designed and fabricated roller bit of 48.2 mm diameter was used. The average speed of
the bit was 50 rpm. Bentonite mud of high viscosity was used during drilling. The rate of
penetration of bit was maintained around 20 mm per minute with vertical pressure up to
150 kPa. The torque was applied upto 0.20 kN-m. These drilling parameters were
maintained for the smooth drilling.
3.5 VERTICALITY OF BOREHOLES
For the assessment of verticality of the boreholes drilled by HA, RR and MDS, an
inclinometer was used for the measurement of deviation of the boreholes from the
vertical. Biaxial inclinometer probe, Sinco-1000 (Slope Indicator Company Seattle
Washington), having two biaxial sensors A and B was used as shown in Fig. 3.6. The
depth intervals of 0.5m were already marked on the cable. As shown in Fig.3.6, the two
sets of wheels are attached to the inclinometer. One accelerometer gives the measure of
the tilt of the inclinometer or the borehole in the plane of the wheels which is assigned as
the reading “A”. The second accelerometer gives the tilt readings in the direction
perpendicular to the plane of the wheels which is assigned as reading “B”. From the tilt
angles, the deviation of the borehole has been calculated as:
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
61
Deviation of Borehole from vertical = L × sin
Where = Angle of tilt measured by inclinometer.
L = Measured interval.
The measured interval was taken equal to the distance between the wheels of the probe
for calculating the lateral displacement.
Fig. 8: Inclinometer apparatus at site
Fig. 3.6 Inclinometer and MDS apparatus at site.
The setting of inclinometer apparatus is shown in Fig. 3.7 and the inclinometer testing at
site is shown in Fig. 3.8.
Inclinometer probe
Cable with depth
interval markings
Read out unit
A & B
Electronic circuit
for Inclinometer
Stand
Mechanical drilling system
Pressuremeter
Pressure system for
pressuremeter
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
62
Fig. 3.7 Setting of Inclinometer apparatus
Fig. 3.8 Inclinometer testing at site
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
63
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
-5.0 0.0 5.0 10.0
Dep
th i
n m
ete
rs
Displacement in mm
MDS RR HA Vertical
Fig. 3.9 Displacement of borehole walls from vertical drilled by MDS, RR and HA.
A comparison of tilt measured by the inclinometer of boreholes drilled by the MDS, RR
and HA is shown Fig.3.9. Inclinometer survey of the boreholes shows that the boreholes
drilled by the MDS remain nearly vertical compared to the boreholes drilled with RR and
HA. Furthermore, with the MDS, the deviation of the borehole walls from the vertical
also remains within the allowable pocket size for the prebored pressuremeter testing. The
allowable diameter of the pocket is 52mm for reduced pressuremeter (RPM). The RPM is
a prebored type of pressuremeter of Cambridge In-situ having 47mm diameter
(Cambridge In-situ Ltd., 2013).
3.6 SMOOTHNESS OF DIAMETER OF BOREHOLES
In order to check uniformity of the hole diameter, the diameter of the boreholes was
measured at 0.5m depth interval in each borehole by the pressuremeter probe. The strain
at which the membrane touches the walls of the borehole was measured. This strain was
used to calculate expansion of the membrane in millimeters. The expansion of the
membrane up to the point it touched the walls of the borehole was added to outer
Vertical Line
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
64
diameter of the probe to find diameter of the borehole. The diameter values of boreholes
drilled by MDS, RR and AH are shown in Fig. 3.10.
A comparison of diameter of boreholes at different depths shows that the diameter of the
borehole drilled by MDS remains nearly constant while control on diameter in AH is
least. The accuracy of diameter by the RR lies in between that by the MDS and AH.
Fig. 3.10 Typical profile of diameter of boreholes drilled by MDS, RR and HA
3.7 DEVELOPMENT OF NEW TECHNIQUE FOR THE DETERMINATION
OF IN-SITU HORIZONTAL STRESS
In the prebored drilling method, stress on the walls of the hole is relaxed when the
sampler is removed from the hole. This relief of stress causes the disturbance in the soil
of the walls and the determination of the in-situ stress becomes difficult by prebored
technique (Clarke, 1995). Further, the initial portion of the elastic stress-strain curve is
also disturbed due to the disturbed zone of the walls. For this purpose, the self-boring
pressuremeter was developed. In self boring technique, the sampler remains in touch with
the walls of the borehole due to which the walls are not relaxed inward. Hence the precise
value of the in-situ stress can be determined in self-boring technique. The cost of the self-
boring technique is much more than the preboring technique. The self-boring technique is
0
2
4
6
8
10
46 48 50 52 54 56
Diameter of borehole (mm)
Dep
th (
m)
MDS RR HA
Initial diameter of borehole = 48.2mm
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
65
complicated, time consuming and requires special experts for the drilling and
pressuremeter testing with the same equipment. There was a need to develop a new
technique of drilling for PBP testing which could produce the same quality results as by
SBP by saving the cost many times.
The New Technique adopted for determining the in-situ horizontal stress comprised the
following steps:
i. The stainless steel (SS) casing with special toothed end was selected for use in
drilling (Fig. 3.11). The movement of deflated probe in stainless steel (SS) casing was
checked (Fig. 3.12). The membrane was inflated in air for achieving 49.5mm
diameter. The pressure required for this extent of inflation was recorded. The drilling
was conducted by the MDS along with insertion of the stainless steel (SS) casing
simultaneously. The sampler was inserted in the casing for drilling (Fig. 3.13). A
special SS casing having internal diameter of 49mm with 0.5mm thick walls was used
for pressuremeter testing.
ii. The SS casing has been provided with sharp teeth at the lower end so that the
diameter of the borehole may remain equal to the outer diameter of the casing with
minimum disturbance to the walls of the borehole.
iii. The casing was inserted with the rotational movement manually. The force for the
rotation was applied at the upper end of the casing.
iv. After one meter drilling, the soil from the internal surface of the casing was wiped
out with circular shape brush.
v. The outer surface of the PBP membrane was slightly lubricated and inserted in the
casing (Fig. 3.14).
vi. The PBP probe was placed at the end of the boreholes.
vii. The cavity pressure inside the PBP membrane was increased until the membrane just
touched the walls of the casing. Let this pressure be denoted by P1.
viii. Before the casing is pulled up, the cavity pressure is increased from P1 to P2 so that
during pulling up of the casing the membrane acquires the inner diameter of the
borehole. The surface of the membrane touched the walls of the borehole
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
66
simultaneously until the whole membrane was in-touch with the walls of the
borehole. Both the processes i.e. pulling up of the casing and the expansion of the
membrane are simultaneous. The casing is pulled up easily as there is very little
resistance between the surface of the membrane and the internal walls of the casing.
During this process very little time is available for the relaxation of the walls of the
borehole.
ix. Now the pressuremeter test was started. The membrane was further expanded to
stress the borehole walls. The pressure at which cavity expansion started was noted as
in-situ horizontal stress.
x. As minimum thickness of the SS tube is selected in this technique hence provision of
threads for joining of the casing pieces was not possible. Due to this consideration,
the casing pieces of 1m, 2m, 3m, 4m and 5m lengths were fabricated for the
pressuremeter tests at 1m, 2m, 3m, 4m and 5m depths respectively.
xi. For the second test, the borehole up to the depth of first test is reamed by the sampler
having diameter 50mm so that the insertion of the casing for the second test may not
encounter friction of the borehole walls up to 1m. In this way the casing had to face
the friction of only 1m soil strata in every test during insertion and pulling up of the
casing.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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67
Fig.3.11 Stain-less steel casing with toothed end for insertion
Fig.3.12 The PMT probe inserted in casing from upper end.
PMT Probe SS casing
SS casing Toothed
end
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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68
Fig.3.13 The sampler being inserted in casing for drilling of borehole
Fig.3.14 The PBP probe being inserted in casing for test
SS casing
PBP probe
SS casing
PBP probe
Sampler
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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69
The pressuremeter test curves obtained for different depths are shown in Fig.3.15 where
the lift-off pressure of the membrane is evident from the curves. The lift pressures of the
test curves as determined from New Technique are given in Fig. 4.32 (chapter-4) and
compared with traditional technique.
0
200
400
600
800
1000
0 10 20 30 40 50
Cavity strain %
Ca
vit
y p
res
su
re,
kP
a
Fig. 3.15 Typical PMT test curves at different depths by New Technique
3.8 IN-SITU TESTING PLAN
A site comprising alluvial soils was selected at 18 km Multan Road, near Lahore city of
Pakistan for this study. Field testing including prebored pressuremeter tests (PMT), cone
penetration tests (CPT) and standard penetration tests (SPT) at four locations, each to 10
m depth. The pressuremeter testing at points designated as PMT(A) have been conducted
by New Technique up to 5m depth. Undisturbed samples were also taken from four
boreholes. The site plan with test locations is shown in Fig. 3.16.
Lift-off
pressure
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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70
Location-1 Location-2
Location-3 Location-4
Fig. 3.16 Test points location plan
Boreholes for the recovery of undisturbed samples (UDS) were drilled by rotary drilling
rig. The UDS were recovered by thin walled Shelby tubes (ASTM D1587) using rotary
drilling rig. The UDS samples were recovered from the field according to the schedule
given in Table- 3.1 which also provides information about the depth and number of
undisturbed soil samples.
CPT
SPT
PMT (A)
UDS
PMT
1m
1m
1m
1m
CPT
SPT
PMT (A)
UDS
PMT
1m
1m
1m
1m
CPT
SPT
PMT (A)
UDS
PMT
1m
1m
1m
1m
CPT
SPT
PMT (A)
UDS
PMT
1m
1m
1m
1m
30m
m
100m
m
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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71
Table 3.1: Schedule of In-situ tests and UDS
Depth
(m)
Location #1 Location #2 Location #3 Location #4
PMT/CPT/SPT UDS PMT/CPT/SPT UDS PMT/CPT/SPT UDS PMT/CPT/SPT UDS
1
2
3
4
5
6
7
8
9
10
3.9 IN-SITU TESTING
Various in-situ testing techniques applied during field testing included PMT, CPT and
SPT. These techniques are common for the soil characterization and are used worldwide
for insitu testing. The details of these techniques are described in succeeding sections.
3.9.1 Pressuremeter testing
The PMT apparatus as shown in Fig. 3.17 was used in the present research. This
pressuremeter was initially developed by Akbar (2001) during his PhD research in the
University of Newcastle Upon Tyne, UK and later modified/improved by Rehman (2010)
during his PhD research at the University of Engineering and Technology, Lahore,
Pakistan. Stress controlled pressuremeter testing was conducted by this prebored
pressuremeter of 305 mm length and 48.2 mm outer diameter probe. The pressuremeter is
strain arm type. Hall Effect Transducer (HET) has been used for the measurement of
displacement of the membrane from the surface of the probe. Two pressure regulators are
installed in this system i.e. high pressure and low pressure regulators. The details of the
electronics system, pressure regulating system and Pico logger are shown in Figs. 3.18,
3.19 and 3.20 respectively.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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72
Fig. 3.17 Prebored pressuremeter apparatus (Rehman, 2010)
Fig. 3.18 Details of electronics box
Output to
data logger
Input from
HET
Input from
Pressure
Transducer
Selector for
Attenuation
Output to
multimeter
Pressuremeter
Electronics Box
Pressure Control
System
Data Logger
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73
Fig. 3.19 Details of pressure regulating system
Fig. 3.20 Pico logger connections
3.9.1.1 Pressuremeter Calibrations for the measurement of pressure and radial
expansion of the membrane are required prior to the start the pressuremeter testing at any
site. The calibration of pressure transducer has been performed for the correct
Signals received
from electronics
box
Signals transmitted
to computer
Connection to
gas cylinder
Low pressure
regulator
High pressure
regulator
Pressure
transducer
Valves to close
pressure lines
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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74
measurement of pressure inside the membrane cavity. The calibration of Hall Effect
Transducer (HET) has been performed for the correct measurement of displacement of
membrane from the outer surface of the probe. The membrane has also been calibrated for
the stiffness so that this stiffness may be subtracted from the observations of stiffness of
soil. The calibrations of pressure transducer, HET and membrane are shown in Figs. 3.21,
3.22 and 3.23 respectively.
Calibration of pressure transducer was conducted before, during and after the testing at
site. The pressure transducer was calibrated by the use of Budenberg dead load tester. The
pressure transducer was installed on the tester and was also attached with electronics box.
A voltmeter was attached with the electronics box for the receiving the signals (in mV)
for increase in pressure. The dead loads were placed on the Budenberg tester in the order
to produce pressure of 100 kPa in each increment. The corresponding signal of pressure
transducer in mV was measured from voltmeter. The plots of change in pressure
transducer voltage (mV) versus pressure measured by Budenberg tester are shown in Fig.
3.21 from which the pressure values can be compared for different degrees of attenuation.
The Fig. 3.21 shows that the attenuation at 5V was used for the low pressures and the
attenuation of 0.5V was used for the high pressures required for the testing of soil sample
from deep levels. As the level of required pressure was increased, the attenuation was
selected corresponding to high pressures. The attenuation can be selected prior to the start
of test.
y = 0.46x
R2 = 1.00
y = 0.7285x
R2 = 1
y = 1.1683x
R2 = 0.9999
y = 3.5049x
R2 = 0.9999
0
500
1000
1500
2000
2500
0 500 1000 1500 2000 2500 3000 3500
Change in Pressure Transducer Voltage, mV
Pre
ssu
re b
y B
ud
en
berg
Gau
ge, kP
a
5V
3V
2V
0.5V
Fig. 3.21 Calibration of pressure transducer for different degrees of attenuation
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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75
Calibration of Hall Effect Transducer (HET) for the radial expansion of the pressuremeter
membrane was conducted by the use of height vernier. When the arms of the expansion
system move outward for the radial expansion of the membrane, the output of the HET is
changed. Hence the HET calibration is required before, during and after the site work.
Before the membrane is fixed on the probe, the HET is calibrated. The HET and the
multimeter were attached with the electronics box. The height vernier was placed on the
table and the expansion arms in a closed position with one arm facing down and the other
upward were set with the height vernier. As the position of the moving part of height
vernier is changed, the expansion arms are opened correspondingly. The expansion of the
arms produces change in the output of the HET which was measured in mV by the use of
multimeter. The HET calibration curve is shown in Fig. 3.22.
y = -5E-05x2 + 0.1196x
R2 = 0.9998
0
5
10
15
20
25
30
35
40
45
50
0 100 200 300 400 500 600
Change in HET output (mV)
Rad
ial
exp
an
sio
n,%
Fig. 3.22 Calibration of Hall Effect Transducer (HET)
Calibration of membrane for stiffness was conducted for the net pressure measurement
during expansion of membrane at certain levels of radial expansion in pressuremeter
testing. The calibration was conducted in following steps:
1. The membrane was installed on the probe.
2. The probe was attached with electronics box.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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76
3. To record the output of the HET and pressure transducer on computer, the electronics box
was attached with the computer through Pico logger.
4. The pressure system was attached with the probe.
5. The pressure transducer was fitted with the pressure system to measure the pressure of the
gas entering the membrane.
6. The membrane was inflated by nitrogen gas.
7. The pressure inside the membrane was increased and the membrane started expanding.
8. Due to the expansion of the membrane, the output of the HET and pressure transducer is
changed which is measured by computer. Two types of readings are measured by the
computer; the output of pressure transducer in mV and the output of HET in mV.
9. The readings of output of HET and pressure transducer recorded in mV were converted to
% expansion and kPa respectively.
10. The plot of the membrane expansion (%) and the pressure (kPa) is shown in Fig.3.23.
The equation of this calibration plot was applied to all the test curves of pressuremeter
testing. The readings of radial expansion were recorded for inflation and deflation.
y = 53.888x0.261
R2 = 0.9911
0
20
40
60
80
100
120
140
160
0 10 20 30 40 50
Radial expansion, %
Cavit
y P
ressu
re, kP
a
Fig.3.23 Calibration of membrane for stiffness
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77
3.9.1.2 PMT Test Methodology covers the set up of PMT apparatus and pressuremeter
testing method. Setup of PMT apparatus was the first step for the prebored pressuremeter
testing at site. The membrane was installed on the pressuremeter probe. Probe was
attached with the electronics box through the cable for the input of HET signals to the
electronics box. The hose pipe of the probe was attached with the pressure regulating
system so that gas may enter the probe to inflate the membrane. Both the regulators (high
pressure and low pressure) were turned to initial position so that the passage of the gas is
cut-off before the start of the test and the pressure of gas may be increased from zero
level. The valves of the pressure lines were also closed. The pressure regulating system
was attached with the nitrogen (N2) gas cylinder. The valves of the gas cylinder were
closed to avoid any sudden increase of pressure in the pressure lines. The electronics box
was attached with the computer through the Pico logger to record the output of the
pressure transducer and the HET. The Pico Log software was installed on the computer to
be used for the testing. The two types of readings are recorded by the Pico Log software;
the pressure inside the probe and the expansion of the membrane. The system was
checked for the leakage of the gas from the probe seals, membrane clamping points,
pressure pipe connected with the probe, regulators, valves of the pressure regulating
system and the point of pressure transducer installation. For this purpose, the probe was
placed in a metal tube of 55mm diameter. The pressure from the cylinder was released
into the system and the low pressure regulator was turned slowly to allow the passage of
gas to the probe. The increase in pressure was monitored from computer. At appropriate
level of pressure, keeping in view the expected level of pressure at site, the valves of the
pressure regulating system were closed and the gas supply was cut off. Waited for five
minutes and checked the loss of pressure by noting the reading of pressure on computer.
When there was almost no loss of pressure, the probe was considered ready for the use.
The membrane was deflated and the valves were again closed. The gas leakage test was
conducted so that the loss of gas and damage to the borehole wall may be avoided. The
gas leakage points were also considered critical for the entrance of water in to the probe
when the membrane is deflated. By conducting the leakage check, the working of the
pressure transducer and HET was also checked which is very important prior to start the
pressuremeter testing in the borehole.
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78
Pressuremeter testing was conducted in the boreholes drilled by two types of techniques;
traditional technique and the New Technique. Firstly, the pressuremeter testing was
conducted in the boreholes drilled by the traditional technique. These boreholes are
shown in the testing plan by „PMT‟. Stress controlled pressuremeter tests were conducted
within 15 minutes after the completion of drilling as recommended by Clarke (1995) so
that the walls of the borehole may not be relaxed. The probe was lowered in borehole in
such a manner that the middle point of the probe was at 1m depth. The low pressure
regulator was turned slowly to increase the pressure in the probe to inflate the membrane.
The pressure (in mV) and the expansion (in mV) of the membrane were monitored on
computer. Readings of pressure and cavity expansion were recorded at 1 second interval
by Pico data logger so that shear modulus at small strain level could be obtained.
Secondly, the pressuremeter testing was conducted in the boreholes drilled by New
Technique. These boreholes are shown in the testing plan as „PMT (A)‟. The boreholes
were drilled with care so that the walls of the boreholes may not be disturbed. The probe
was lowered at the desired depth and the casing was withdrawn up to the upper level of
the probe. The remaining steps of the procedure were same as for traditional technique.
The pressuremeter testing at site is shown in Fig. 3.24.
Fig. 3.24 Pressuremeter testing at site
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79
3.9.1.3 PMT Test Results in the form of cavity strain (%) and cavity pressure (kPa) are
shown in Figs. 3.25 and 3.26. The typical PMT test curves for CL-ML soil up to 3m
depth are shown in Fig. 3.25. Test curves for ML soil from 4m to 10m are shown in Fig.
3.26. The test curves at different depths show different cavity pressures, which is due to
the different overburden pressure at different depths. The difference in cavity pressures is
also due to the difference of moisture content and density at four locations of the site.
The cavity pressure was increased up to the limit where the cavity strains up to 41% were
achieved. The achievement of cavity strain of 41% during pressuremeter testing was
necessary so that the pressuremeter test curves may be used for the determination of limit
pressure, which is determined at 41% cavity strain (Clarke, 1995). The pressure and
cavity strain readings were taken at 1 second time interval. In Figs. 3.25 and 3.26, some
readings have been omitted so that the data points of the test curves may be seen clearly.
0
100
200
300
400
500
600
700
0 5 10 15 20 25 30 35 40 45
Cavity strain,%
Cavit
y p
ressu
re,K
Pa
1m 2m 3m
Fig. 3.25 Typical PMT curves from 1m to 3m depths
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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80
0
200
400
600
800
1000
1200
1400
1600
1800
0 10 20 30 40 50
Cavity Strain, %
Cav
ity P
res
su
re,
KP
a
4m 5m 6m 7m 8m 9m 10m
Fig. 3.26 Typical PMT curves from 4m to 10m depths.
3.9.2 Cone Penetration Testing (CPT)
The CPT were performed using electrical piezocone as per ASTM D5778. The CPT were
conducted for the determination of cone tip resistance (Qc) by the penetration of conical-
shaped penetrometer, Sleeve friction (fs) of a cylindrical shaped sleeve located behind the
cone and friction ratio (Rf) which is the ratio of fs to Qc.
3.9.2.1 CPT Apparatus comprised Pagani cone penetration apparatus. The cone
attached with the sleeve is connected to the data logger and computer for recording the
data. The sensors for the pore water pressure and inclination of the sleeve with respect to
the vertical were also attached with the cone and sleeve assembly. The CPT apparatus
was calibrated before the start of the field testing.
3.9.2.2 CPT Test Methodology The rig to conduct the CPT at site was installed on
location to be tested. Heavy anchors were installed in to the ground to balance the upward
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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81
reaction of the rig during the penetration of the cone. The electrical piezocone was
penetrated at the steady rate of 2cm/second to obtain continuous profiles of soil
resistance. The CPT readings were recorded at 1cm depth interval.
The continuous profiles of Qc, fs and Rf are shown in Appendix-A.
3.9.3 Standard Penetration Testing (SPT)
Standard penetration tests were performed in boreholes drilled by rotary drilling rig at one
meter depth interval according to ASTM-D-1586. The tripod for the performance of SPT
was set at the borehole location. The split spoon sampler was attached at one side of the
rod and other rods were also attached according to the depth at which the test was to be
conducted. The mass of the hammer used was 63.5 kg for the SPT blows. The drill rod,
which was exposed above the ground level, was marked at three locations each 150mm
apart. The guide rod was attached to the upper part of the rod above ground level. The
guide rod was marked at 760mm for dropping the hammer manually. The SPT blows
were counted for the penetration of 450mm (150mm x 3). The blows for 300mm
penetration were taken as SPT blows for the strata of that particular depth. The test was
terminated according to the criterion given in ASTM D1586. The disturbed samples were
recovered by split spoon sampler from one meter depth interval up to 10m depth from
four locations as shown in Fig. 3.27. The SPT profiles of the boreholes at 4 locations are
shown in Appendix-B.
Fig. 3.27 Disturbed sample from SPT sampler
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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82
3.10 LABORATORY TESTING
The laboratory testing for the present research comprised resonant column tests, triaxial
tests, direct shear tests, unconfined compression tests and classification tests. For the
strength tests, the preservation and preparation of the specimen by sophisticated technique
is most important task for best quality results.
3.10.1 Preservation of Samples
The preservation of the samples is very important task in laboratory testing. The samples
recovered from the boreholes by the Shelby tubes were waxed at both ends of the tube by
placing circular thin wooden pieces at the end so that the sample may not move inside the
tube. The tubes were placed in boxes in vertical position of the sample as was in-situ. The
samples were placed the in the controlled humidity and temperature room to protect the
samples from drying as the temperature and humidity variation can cause change in the
natural moisture content of the samples and the minor change in the moisture content can
cause change in the strength properties of the soil.
3.10.2 Undisturbed Specimen Preparation
To avoid the disturbance incorporated during the sample preparation, the undisturbed
specimens were prepared in the following steps:
i. The split mould of 38mm internal diameter and 76mm height for preparation of
specimens for triaxial and unconfined compression testing and split mould with
50mm internal diameter and 100mm length for resonant column testing was selected.
ii. The split mould was screwed and the membrane was set inside the mould as shown in
Fig. 3.28.
iii. The sample cutter was attached at one side of the split mould.
iv. The Shelby tube containing the sample was cut into pieces according to the lengths
required for the tests like resonant column, triaxial and unconfined compression tests.
v. The cut portion of the Shelby tube was fixed in the mechanical extruder of variable
speed.
vi. The mould with collar and the cutter were positioned in the mechanical extruder as
shown in Fig. 3.29.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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83
vii. The vacuum system was attached with split mould so that the membrane may not be
folded and assured to remain fully in touch with the internal surface of the mould.
This vacuum (negative pressure) application protects the specimen from disturbance.
viii. The sample was pushed up very slowly at the rate of 1cm/minute to allow the sample
to enter in to the mould (Fig. 3.30).
ix. The mould with collar and cutter was removed from the extruder.
x. After removing collar and cutter, the soil from the both ends was trimmed. The
specimen with 38mm diameter and 76mm length was prepared by this procedure.
xi. The specimen was placed on the lower end platen of the cell along with the screwed
mould.
xii. The upper end platen was placed on the top face of the specimen.
xiii. The membrane from both sides of the mould was stretched on the lower and upper
end platen.
xiv. The membrane was tightened on the platens with O-rings.
xv. The vacuum lines were detached from the mould and the vacuum was applied from
the lines of lower and upper end platens.
xvi. The split mould was unscrewed and removed.
xvii. The cell was filled with water and the air pressure applied up to 15 kPa
simultaneously as the vacuum was removed.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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84
Fig. 3.28 Split mould with membrane attached vacuum system
Fig.3.29 Assembled split mould with base collar and cutter.
Collar Membrane
Split mould
Cutter Vacuum lines
Cutter
Split mould
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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85
Fig. 3.30 Mechanical extruder with mould and cut piece of Shelby tube.
3.10.3 Triaxial Tests
Twenty (20) triaxial (CIU and CID) tests with unload-reload loops were conducted. The
samples were installed in the triaxial cells and then subjected to saturation phase. The
samples were saturated by applying back pressure technique for CL-ML and ML samples.
Both CL-ML and ML samples were saturated up to B = 0.98 where B is the Skempton‟s
pore pressure parameter and then subjected to effective consolidation stress ((c′)) equal
to the overburden stress which was determined from the depth from where the samples
were recovered. The setup of triaxial test apparatus during the test is shown in Fig. 3.31.
Undrained condition for isotropically consolidated undrained (CIU) triaxial tests and
drained condition for isotropically consolidated drained (CID) triaxial tests were
maintained throughout the shearing phase of CL-ML and ML samples respectively. The
samples were sheared up to 20% strain. CIU tests were performed on CL-ML samples
according to (ASTM D-4767) and CID tests were performed on ML samples according to
(ASTM D-7181), strain controlled in each case. Monotonic loading was applied
throughout the shearing phase. The pressuremeter test is a static test hence to compare
unload, reload and unload-reload stiffness, the unload-reload loops were included in CIU
Vacuum lines
Split mould
Shelby tube
Mechanical
Extruder
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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86
and CID triaxial tests. The loops were performed by decreasing and increasing the
deviator stress. The conditions of selecting the extent of unload pressure; the criterion
used for the pressuremeter tests, was applied for the unload-reload loops of the triaxial
tests for CL-ML and ML samples.
Fig. 3.31 The triaxial test in progress
3.10.4 Triaxial Tests with Unload-reload Loops
Typical stress-strain curves of triaxial tests (CIU and CID) with unload reload loops
obtained in CL-ML and ML soils at different effective stress are shown in Figs.3.32 and
3.33.
The Fig. 3.32 shows the test curves for CIU tests for the samples taken from CL-ML soil.
The samples were tested at different effective stresses as shown in the Fig. 3.32. The Fig.
3.33 shows the test curves for CID tests for the samples taken from ML soil. The samples
were tested at different effective stresses as shown in the Fig. 3.33.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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87
0
50
100
150
200
250
0 5 10 15 20 25
Axial strain, %
Devia
tor
str
ess, K
Pa
Effective stress = 18 KPa Effective stress = 35 KPa Effective stress = 55 KPa
Fig. 3.32 Typical stress-strain curves of CIU triaxial test with unload-reload loops for
CL-ML soil.
0
100
200
300
400
0 5 10 15 20 25
Axial strain, %
De
via
tor
str
ess
, K
Pa
Effective stress = 65 KPa Effective stress = 80 KPa
Effective stress = 125 KPa
Fig. 3.33 Typical stress-strain curves of CID triaxial test with unload-reload loops for
ML soil.
Increase in
Deviator
Stress
Increase in
Deviator
Stress
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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88
3.10.5 Resonant Column Tests
The resonant column tests were performed on both cohesive (CL-ML) and cohesionless
(ML) soils. The specimens were prepared as described in section 3.10.2.
Fig. 3.34 Resonant column apparatus used for testing.
The details of the electromagnet system of resonant column apparatus are shown in Fig.
3.34 and the complete apparatus used during the testing is shown in Fig. 3.35. The
samples were saturated by applying back pressure technique. The specimens were
consolidated in four stages. In every stage the effective stress is increased and the sample
was drained at that effective consolidation stress. The effective consolidation stresses
were selected as 100 kPa, 200 kPa, 300 kPa and 400 kPa. In four stages the Gmax values
were evaluated at small shear strains of 10-4
%. After the 4th
stage of confining pressure,
the amplitude of vibration was gradually increased due to which the strain was increased.
It has been observed that by increasing the strain, the shear modulus is decreased. The
typical resonant column test data for ML soils is shown in Fig. 3.36. This decrease in
shear modulus shows the degradation of dynamic shear modulus.
Soil specimen
Pressure panel
Electromagnet
system
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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89
Fig.3.35 Resonant column test in progress
20
40
60
80
100
0.0001 0.001 0.01 0.1
Dynamic shear strain (), %
Dy
na
mic
sh
ea
r m
od
ulu
s(G
) (
Mp
a)
Fig.3.36 Typical resonant column test data
The damping ratio can also be determined from resonant column tests at the same shear
strain level at which the G values are determined. The results of G/Gmax and damping
P′=400 kPa
Decrease in
Shear Modulus
P′=300 kPa
P′=200 kPa
P′=100 kPa
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
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90
ratio determined from resonant column tests for CL-ML and ML soils are given in
Appendix-C.
3.10.6 Unconfined Compression Tests
The unconfined compression (UC) tests were performed according to the ASTM D-2166.
UC tests were conducted on undisturbed samples taken from thin walled tubes by placing
the cut portion of the tube in the hydraulic extruder to transfer the sample from thin
walled tubes to the mould of 38mm diameter and 76mm length. The sample from the
mould was recovered by a small extruder. This extrusion along with trimming of the extra
annulus with sharp edge knife was performed with much care. The upper and the lower
surface of the sample was trimmed carefully so that these surfaces may be exactly at right
angle to the longitudinal axis of the sample for assurance of uniform distribution of stress
during shearing. Then the sample was installed on unconfined compression machine for
the performance of test.
The results are shown in the summary of test results in Tables-3.2, 3.3, 3.4 and 3.5.
3.10.7 Direct shear tests
Direct shear tests were conducted on cohesionless (ML) soils. The tests on each sample
were conducted for three normal stress values. The middle normal stress value was taken
equal to overburden stress calculated on the basis of depth of the sample in-situ. The
angle of internal friction values were determined from the results of direct shear test.
The results are shown in the summary of test results in Tables-3.2, 3.3, 3.4 and 3.5.
3.10.8 Soil Classification Tests
The soil classification tests i.e. grain size analysis (ASTM-422) and liquid & plastic limit
(ASTM D-4318) tests were conducted on the disturbed samples recovered from SPT split
spoon sampler. Dry density (ASTM D-698) and natural moisture content (NMC) (ASTM
D- 2216) were determined from undisturbed soil samples (UDS). The soil was classified
according to Unified Soil Classification System (ASTM D-2487) as CL-ML and ML. The
results are shown in the summary of test results in Tables-3.2, 3.3, 3.4 and 3.5.
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
91
Table 3.2 Summary of Soil Classification, NMC, Dry Density, Unconfined
Compression and Direct Shear Test Results (Location 1)
Location
No Depth
Soil Classification Symbol Dry
density NMC Su(UCT)
Direct
Shear
Test
Gravel Sand Silt Clay LL PL PI g/cm3 % kPa ′
m % % % % % % % deg
1 1 2 8 70 20 26 20 6 CL-ML 1.567 11.92 71.2
2 3 7 65 25 26 19 7 CL-ML 1.582 12.11 83.3
3 0 10 71 19 25 19 6 CL-ML 1.561 12.21 64.3
4 0 24 68 8 NP ML 1.532 10.52 26.5
5 0 22 71 7 NP ML 1.527 9.13 26.7
6 0 26 67 7 NP ML 1.519 8.81 27.3
7 1 29 65 5 NP ML 1.548 9.64 29.1
8 0 33 62 5 NP ML 1.552 8.37 28.6
9 0 36 60 4 NP ML 1.567 8.42 29.7
10 0 38 57 5 NP ML 1.591 10.88 30.2
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
92
Table 3.3 Summary of Soil Classification, NMC, Dry Density, Unconfined
Compression and Direct Shear Test Results (Location 2)
Location
No Depth
Soil Classification Symbol Dry
density NMC Su(UCT)
Direct
Shear
Test
Gravel Sand Silt Clay LL PL PI g/cm3 % kPa ′
m % % % % % % % deg
2 1 1 3 71 25 25 18 7 CL-ML 1.571 15.98 78.4
2 3 8 63 26 26 19 7 CL-ML 1.569 15.23 72.9
3 0 18 61 21 24 18 6 CL-ML 1.553 16.29 62.7
4 0 20 71 9 NP ML 1.543 12.52 27.7
5 0 22 69 9 NP ML 1.528 11.23 26.6
6 0 27 66 7 NP ML 1.543 9.22 28.2
7 0 30 65 5 NP ML 1.543 8.47 29.5
8 0 32 63 5 NP ML 1.549 10.33 28.1
9 0 35 61 4 NP ML 1.531 9.04 27.8
10 0 37 59 4 NP ML 1.556 11.20 29.7
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
93
Table 3.4 Summary of Soil Classification, NMC, Dry Density, Unconfined
Compression and Direct Shear Test Results (Location 3)
Location
No Depth
Soil Classification Symbol Dry
density NMC Su(UCT)
Direct
Shear
Test
Gravel Sand Silt Clay LL PL PI g/cm3 % kPa ′
m % % % % % % % deg
3 1 1 4 69 26 26 19 7 CL-ML 1.592 11.44 83.7
2 4 6 66 24 26 19 7 CL-ML 1.592 13.53 80.1
3 0 20 66 14 24 19 5 CL-ML 1.574 10.70 77.6
4 0 18 73 9 NP ML 1.531 10.43 27.8
5 1 24 68 7 NP ML 1.533 11.24 26.4
6 0 24 67 9 NP ML 1.542 10.52 28.5
7 1 30 62 7 NP ML 1.557 10.31 28.8
8 0 33 62 5 NP ML 1.562 8.53 29.1
9 0 32 59 9 NP ML 1.571 8.22 29.7
10 0 36 58 6 NP ML 1.574 11.67 29.2
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
94
Table 3.5 Summary of Soil Classification, NMC, Dry Density, Unconfined
Compression and Direct Shear Test Results (Location 4)
Location
No Depth
Soil Classification Symbol Dry
density NMC Su(UCT)
Direct
Shear
Test
Gravel Sand Silt Clay LL PL PI g/cm3 % kPa ′
m % % % % % % % deg
4 1 2 6 68 24 26 19 7 CL-ML 1.651 12.31 87.3
2 3 7 67 23 26 19 7 CL-ML 1.617 13.34 66.7
3 0 12 68 20 24 18 6 CL-ML 1.607 11.20 57.6
4 0 19 72 9 NP ML 1.529 9.21 26.3
5 1 19 71 9 NP ML 1.527 9.33 26.6
6 0 24 67 9 NP ML 1.543 9.42 27.2
7 0 26 66 8 NP ML 1.561 8.88 28.6
8 0 30 63 7 NP ML 1.553 10.33 29.8
9 0 31 62 7 NP ML 1.544 9.23 28.4
10 0 33 60 7 NP ML 1.569 11.45 29.1
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
95
3.10.9 Soil Profile
Soil profile of substrata as shown in Fig. 3.37 was established by various physical
properties of the subsurface soils within 10 m depth as shown in summaries of test results
in Tables 3.2, 3.3, 3.4 and 3.5.
Fig. 3.37 Soil profile at site
3.11 SUMMARY
A mechanical drilling system (MDS) was developed for the drilling of vertical and
constant diameter boreholes for prebored pressuremeter testing. It is light weight drilling
system which can be used for drilling of boreholes with helical and slotted type samples
up to 10m depth.
The pressuremeter tests were conducted in the boreholes drilled by MDS, hand auger and
rotary rig. The verticality of the boreholes drilled by these three methods was determined
by the inclinometer. The diameter of the boreholes drilled by these methods was also
compared.
A new Technique for the determination of in-situ horizontal stress has been developed. A
specially fabricated equipment was used in this technique. This technique was applied for
borehole drilling and in-situ horizontal stress was determined.
In-situ tests were conducted in alluvial soils and laboratory tests were conducted on the
samples recovered from the site. The in-situ tests included pressuremeter testing, cone
penetration testing (CPT) and standard penetration testing (SPT). The laboratory tests
CL-ML soil
ML soil
0m
3m
10m
NSL
Sandy Silt/silt
with sand
Silty clay
CHAPTER-3 DEVELOPMENT OF DRILLING SYSTEM, IN-SITU
TESTING AND LABORATORY TESTING
96
conducted on the samples were resonant column dynamic test, triaxial tests with unload-
reload loops, direct shear tests, unconfined compression tests and classification tests.
CHAPTER-4
97
ANALYSIS AND DISCUSSION ON RESULTS
4.1 INTRODUCTION
The results of in-situ and laboratory tests have been presented in chapter-3. This chapter
presents analysis of the data to establish quality of boreholes drilled, determination of
shear modulus from PMT and triaxial, development of new correlations between in-situ
and laboratory tests results for the geotechnical characterization of the on-site soils.
4.2 COMPARISON OF QUALITY OF PMT CURVES
The investigation plan for the comparison of different drilling modes is described in
chapter-3.
Fig. 4.1 shows a typical test curve obtained in a borehole drilled by the Mechanical
Drilling System (MDS) at 4m depth for the elaboration of three phases of a good quality
prebored pressuremeter curve. Phase-I (P-I) shows that the probe attains the diameter of
the borehole and the membrane just touches the wall of the borehole whereas phases II &
III show the pseudo-elastic (micro plastic) and plastic deformations respectively. Shape of
the curve indicates a good quality pressuremeter curve which is possible in a precisely
drilled borehole.
It is evident from the pressuremeter curves of MDS boreholes in Figs. 4.2 and 4.3 that the
stress starts from about 1.5 to 2.5% strain and unloading starts at about 41.5% strain.
Hence about 40 % net strain range is available for the analysis and a number of unload-
reload loops can be formed in this strain range for stiffness evaluation. Furthermore,
cavity expansion to 41.5% is closer to the criterion for the pressure to double the cavity
volume i.e. 41% cavity strain (Clarke, 1995), hence pressuremeter curves in MDS
boreholes can be analyzed to estimate limit pressure.
Figures 4.2 & 4.3 show a comparison of PMT curves obtained in boreholes drilled by
hand auger, rotary rig and MDS in CL-ML and ML soils respectively. In Fig. 4.2, the
pressuremeter test curves show that stress starts increasing at about 2.5% to 4% cavity
strain in case of MDS and RR holes and at about 7% cavity strain in hand auger holes
(HA). Strains at the start of RR and MDS curves shows that the MDS is as good as RR
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
98
for constant diameter of the borehole. The RR and MDS curves show the phases I, II and
III clearly which is the characteristic of a good quality borehole (Tarnawski, 2004).
However, curvature of PMT test curve for MDS is showing three phases more clearly
hence MDS curves are better shaped than RR. The slow increase in stress in HA curves
depicts disturbance of the borehole walls. The pressuremeter curves in boreholes with
disturbed walls will provide underestimated pressuremeter modulus (Tarnawski, 2004). In
HA-2m curve, the unload-reload loops are not good shaped due to disturbance produced
by hand augering. HA-2m and HA-3m curves do not have distinct Phase I and Phase II
indicating poor quality test curves.
In Fig. 4.3, the PMT test curves performed in the boreholes drilled by MDS and RR
show good resemblance, however PMT curves obtained in the MDS boreholes show even
better shape showing phases I, II and III more clearly than RR. The HA-6m and HA-8m
curves shows that most of the strain range was lost due to large diameter of the boreholes
and sufficient strain range was not available for unload-reload loops. In HA curves the
increase of stress in Phase I is not gradual and there is distinct increase of stress/strain
gradient. This distinct stress/strain gradient shows undisturbed walls of the borehole
(Baguelin et al. 1978).
Fig. 4.1 Phases of a good quality prebored pressuremeter curve
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
99
0
200
400
600
800
1000
0 10 20 30 40 50
Cavity strain %
Ca
vit
y p
res
su
re,
KP
a
RR--2m RR--3m MDS--2m MDS--3m HA--2m HA--3m
ASTM typical range for
diameter tolerence
Fig. 4.2 Typical PMT curves in CL-ML soil by RR, MDS and HA
Fig. 4.3 Typical PMT curves in ML soil by RR, MDS and HA.
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
100
Smoothness of the borehole walls is difficult to be achieved by hand auger because it has
no control of vertical drilling. The drilling rig may not provide smooth surface of the
borehole walls because of vibration of the drilling bit.
Above comparison indicates that the MDS is able to drill vertical boreholes of constant
diameter. Hence the MDS can be used in PMT study with confidence for achieving the
good quality PMT results.
Fig. 3.9 (Chapter-3) shows that the boreholes drilled by MDS are nearly vertical as
compared with the boreholes drilled by hand auger and rotary rig. The Fig. 3.10 (Chapter-
3) shows that the diameter of the borehole drilled with the MDS is almost constant as
compared with the boreholes drilled by hand auger and rotary rig.
The three drilling techniques have been compared for drilling boreholes for pressuremeter
tests up to 10m depth in CL-ML and ML soils for quality and financial aspects in Table
4.1. The cost has been estimated at the prevailing rates in Pakistan.
Table-4.1: Comparison of Different Modes of Drilling in Soil
Item Hand Auger Rotary Rig MDS
Cost of fabrication, $ 100 6000 400
Weight 10 kg 1500 kg 80 kg
Transportation mode small vehicle Truck small vehicle
Transportation cost 0.5$/km 5$/km 1$/km
Setting time at site 1hr 8hrs 1hr
Time for quality drilling 1.5m/hr 2m/hr 1m/hr
Labour cost for drilling 1.5 $/m 2.5$/m 1$/m
Total cost for drilling 1.5 $/m 5.5$/m
(i/c cost of fuel) 1$/m
Lateral movement/ vibration Lateral
movement Vibration
No Lateral
movement /No
vibration
Inclination Yes No No
Type of sample Disturbed Undisturbed/
Disturbed Disturbed
Constant diameter Difficult Easy Very easy
Smoothness of borehole wall Very Difficult Difficult Very easy
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
101
It is evident from Table 4.1 that cost of the MDS manufacturing and drilling is much less
than that of the drilling rig whereas quality of borehole in terms of regular diameter,
smoothness and verticality is much better than that by RR. The MDS can not be used in
gravely soils. However MDS can be used in CL-ML and ML soils effectively.
4.3 SHEAR MODULUS
Shear moduli were determined from the unload-reload loops of the prebored
pressuremeter and triaxial tests curves and compared for the specific strain ranges.
4.3.1 Secant Shear Moduli (Gur , Gu and Gr ) from PMT
Data of forty PMT test curves were analyzed for the determination of unload-reload
secant shear modulus (Gur) from unload-reload loops. The shear moduli (Gur) were
determined from the slope of the line joining the apex (max, P1) and (min, P2) of the loop
as shown in Fig. 4.5. The slope of the line is equal to 2 times the Gur (Bellotti et al, 1989).
It was observed that there is non-linear hysteretic behavior in all the loops. Similar
findings have been reported by Clarke (1995).
The secant moduli (Gu and Gr) from PMT were determined from unload and reload
portions of the unload-reload loops for which the method is shown in Fig.4.4. For the
unload secant modulus (Gu), the point of maximum strain (max) and relevant pressure P1
on the unload portion was selected as origin for the strain and pressure respectively. For
the reload secant modulus (Gr), the point of minimum strain (min) on the reload portion
and relevant pressure P2 was selected as origin for the strain and pressure respectively.
The slope of the line joining the two points on reload portion (from origin of minimum
stress and strain to the points 1,2,3,4 and 5 shown for reload portion in Fig.4.4) was taken
equal to 2 times of reload secant modulus Gr (Clarke, 1995) i.e. 2Gr. The same method
was adopted for Gu. Typical unload-reload loops from the PMT curves are shown in Figs.
4.5 & 4.6 along with the Gur values. The strain and stress amplitudes along with equation
for the slope of the line joining the two apices are also shown in Figs. 4.5 & 4.6. The
Gur(PMT) were calculated on the basis of cavity strain (Figs. 4.5 & 4.6) and as the Gu(PMT)
and Gr(PMT) have been calculated on transformed strain approach (Jardine, 1991) for the
purpose of comparison with triaxial tests data, hence these moduli have been shown
separately in Figs. 4.13, 4.14, 4.15 and 4.16.
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
102
Fig.4.4: Method for the calculation of secant moduli Gu(PMT) and Gr(PMT).
y = 48.421x - 8.2919
0.21
0.25
0.29
0.33
0.37
0.173 0.175 0.177 0.179
Cavity strain
Cavit
y P
ressu
re,M
Pa
y = 39.591x - 10.135
0.25
0.29
0.33
0.37
0.41
0.45
0.262 0.264 0.266 0.268 0.27
Cavity strain
Cavit
y P
ressu
re,
MP
a
Fig. 4.5: Typical unload–reload loops (1 & 2) of PMT for CL-ML soil at 3m depth
0.080
0.090
0.100
0.110
0.120
0.130
0.140
0.150
0.1742 0.1744 0.1746 0.1748 0.1750 0.1752
Cavity Strain
Cavit
y P
ressu
re (
MP
a)
Gur = 24.21 MPa
Strain Amplitude = 0.00164
Stress Amplitude = 0.07941 MPa
LOOP-1
Gur = 19.79 MPa
Strain Amplitude = 0.00242
Stress Amplitude = 0.09581 MPa
LOOP-2
P2 for min
min
P1 for max
max
Reloading Curve
Unloading Curve
1
2
3 4
5
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
103
y = 95.914x - 20.414
0.60
0.70
0.80
0.90
1.00
0.215 0.22 0.225 0.23
Cavity strain
Cavit
y P
ressu
re,
MP
a
y = 94.697x - 25.922
0.65
0.75
0.85
0.95
1.05
1.15
0.275 0.28 0.285 0.29
Cavity strain
Cavit
y P
ressu
re,
MP
a
Fig. 4.6: Typical unload–reload loops (1 & 2) of PMT for ML soil at 9m depth
In Figs.4.5 & 4.6, it is evident that the Gur(PMT) values in the two unload-reload loops of
the same PMT test curve differ in magnitude due to the variation of strain and stress
amplitude. Hence for the precise interpretation of shear modulus, the strain magnitude
should be stated with shear modulus values as described by Kondner (1963), Robertson
and Hughes (1986) and Bellotti et al. (1986). So the Figs. 4.5 & 4.6 show that the value of
shear modulus depends on the level of stress and the amplitude of the strain at which the
shear modulus was measured as mentioned by Jamiolkowsky et al. (1985). Hence, Gur
without mentioning stress and strain amplitude is less valuable.
Unload-reload shear moduli Gur(PMT), calculated from the unload-reload loops of
pressuremeter curves on cavity strain basis, are shown in Fig. 4.7. The trend of Gur(PMT)
values shows that there is overall increase in shear modulus with depth. The different
values of shear modulus at the same depth may be due to variation of density and
moisture of soil in different boreholes. Hence at the same depth in different boreholes, the
stiffness is different.
LOOP-1
Gur = 47.96 MPa
Strain Amplitude = 0.0022
Stress Amplitude = 0. 2119 MPa
LOOP-2
Gur = 47.35 MPa
Strain Amplitude = 0.0031
Stress Amplitude = 0.2935 MPa
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
104
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80 100
Gur(PMT), MPaD
ep
th,m
Fig. 4.7: Profiles of Gur (PMT)
Gur(PMT) values of CL-ML soils shown in Fig. 4.7 are comparable with the typical range
of shear modulus from PMT in clayey soils reported by Houlsby & Withers (1988).
Gur(PMT) values of ML soils resemble with the typical range of shear modulus in silts
determined from the PMT by Howie (1991). The profiles of Gur(PMT) in Fig.4. 7 show the
overall increasing trend with depth. Similar trend with depth was reported by Howie
(1991) in silts and Houlsby & Withers (1988) in clays.
4.3.2 Secant Shear Moduli (Gur , Gu and Gr ) from Triaxial
Data of twenty triaxial tests with unload-reload loops were analyzed. The unload-reload
moduli of elasticity Eur(TXL) from triaxial loops were determined from the slope of the line
joining the apices of the unload-reload loop. The unload-reload Young‟s moduli of
elasticity Eur(TXL), from the triaxial tests were converted to Gur(TXL) by using the relation
CL-ML soil
ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
105
Gur = Eur / 2 (1+) (Bowles, 1996) where Poisson‟s ratio () =0.5 (Bowles, 1996) for CL-
ML considering the undrained loading, and 0.3 (Bowles, 1996) for ML soils. Typical
unload-reload loops of triaxial tests along with values of Gur(TXL), strain amplitude and
stress amplitude and equation for the slope of the line joining the two apices of the loops
are shown in Figs.4.8 & 4.9.
Similarly the unload secant modulus of elasticity (Eu) and reload secant modulus of
elasticity (Er) were determined from unloading and reloading portions of the unload-
reload loops respectively. The method described in Fig.4.4 was used to calculate unload
and reload secant moduli Eu and Er from triaxial loops. For the determination of unload
secant moduli, Gu(TXL), the point of maximum strain (max) on the loop was selected as
origin for calculating pressure and strain between two points on the unloading curve.
Similarly for the reload secant moduli, Gr(TXL), the point of minimum strain (min) on the
reloading curve was selected as origin for calculating pressure and strain between the two
points on the reloading curve.
The Eu and Er were converted into shear moduli Gu and Gr respectively by using
Poisson‟s ratio. Typical values of unload secant modulus (Gu) and reload secant modulus
(Gr) along with relevant strain and stress are also shown in Figs. 4.8 & 4.9. All the three
moduli, Gur, Gu and Gr were determined on the basis of axial strain. The unloading of the
loops was performed in elastic limit as described by Wroth (1982) for pressuremeter
loops so that the unload-reload loops of triaxial may be simulated with those of
pressuremeter tests.
Axial strain of triaxial tests was converted to shear strain for the purpose of comparison of
shear moduli of triaxial and pressuremeter tests in degradation curves. The shear strain for
triaxial tests was taken as 1.5 times the axial strain (Terzaghi et al. 1996).
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
106
y = 63.506x - 4.6245
0.06
0.08
0.10
0.12
0.14
0.16
0.0740 0.0744 0.0748 0.0752 0.0756
Axial strain
Pre
ssu
re,
MP
a
y = 58.474x - 6.4395
0.06
0.08
0.10
0.12
0.14
0.16
0.1115 0.1119 0.1123 0.1127 0.1131
Axial strain
Pre
ssu
re, M
Pa
y = 58.523x - 8.6414
0.06
0.08
0.10
0.12
0.14
0.16
0.1490 0.1495 0.1500 0.1505
Axial strain
Pre
ssu
re,
MP
a
y = 60.05x - 10.375
0.06
0.08
0.1
0.12
0.14
0.16
0.174 0.1744 0.1748 0.1752 0.1756
Axial strain
Pre
ssu
re,
MP
a
Fig. 4.8: Typical unload-reload loops (1, 2, 3 & 4) of static triaxial (CIU) test for CL-ML
soil at 2m depth
Gur = 21.17 MPa
Strain Ampl.= 0.000705, Stress Ampl= 0.04474 MPa
MPa
Typical Unload Secant Modulus = 23.07 MPa
Strain = 0.0005794, Stress = 0.04011 MPa
Gur = 19.507 MPa
Strain Ampl= 0.000689, Stress Ampl= 0.040294 MPa
Gur = 19.49 MPa
Strain Ampl= 0.000687, Stress Ampl = 0,040144 MPa
Typical Unload Secant Modulus = 21.7 MPa
Strain = 0,000561, Stress = 0.03662 MPa
Typical Reload Secant Modulus = 21.0 MPa
Strain = 0.000625, Stress = 0.03935 MPa
Typical Unload Secant Modulus = 21.0 MPa
Strain = 0.00056, Stress = 0.03556 MPa
Typical Reload Secant Modulus = 21.6 MPa
Strain = 0.00063, Stress = 0.04059 MPa
Gur = 20.0166 MPa
Strain Ampl= 0.00072 , Stress Ampl = 0.04322 MPa
Typical Unload Secant Modulus = 23.5 MPa
Strain = 0.000595, Stress = 0.04192 MPa
Typical Reload Secant Modulus = 22.05 MPa
Strain = 0.000625, Stress = 0.04137 MPa
Typical Reload Secant Modulus = 22.92 MPa
Strain = 0.0006254, Stress = 0.04301 MPa
LOOP-1 LOOP-2
LOOP-3 LOOP-4
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
107
y = 84.017x - 6.1051
0.10
0.14
0.18
0.22
0.0740 0.0744 0.0748 0.0752 0.0756
Axial strain
Pre
ssu
re, M
Pa
y = 83.977x - 9.2491
0.11
0.15
0.19
0.23
0.1116 0.1120 0.1124 0.1128
Axial strain
Pre
ssu
re, M
Pa
y = 77.383x - 11.413
0.11
0.15
0.19
0.23
0.1492 0.1496 0.1500 0.1504
Axial strain
Pre
ssu
re, M
Pa
y = 85.678x - 14.808
0.11
0.15
0.19
0.23
0.174 0.1744 0.1748 0.1752
Axial strain
Pre
ssu
re,
MP
a
Fig. 4.9: Typical unload-reload loops (1, 2, 3 & 4) of static triaxial (CID) test for ML soil
at 4 m depth.
Gur = 32.31 MPa
Strain Ampl. = 0.000705, Stress Ampl. = 0.05919 MPa
MPa
Typical Unload Secant Modulus = 35.9 MPa
Strain = 0.000579, Stress = 0.05404 MPa
Gur = 29.76 MPa
Strain Ampl. = 0.000699, Stress Ampl. = 0.05405 MPa
Gur = 32.30 MPa
Strain Ampl. = 0.000687, Stress Ampl. = 0.05765 MPa
Typical Unload Secant Modulus = 35.6 MPa
Strain = 0.00056, Stress = 0.05201 MPa
Typical Reload Secant Modulus = 34.6 MPa
Strain = 0.00063, Stress = 0.05623 MPa
Typical Unload Secant Modulus = 33.09 MPa
Strain = 0.0006985, Stress = 0.05405 MPa
Typical Reload Secant Modulus = 32.07 MPa
Strain = 0.00075, Stress = 0.05442 MPa
Gur = 32.95 MPa
Strain Ampl. = 0.00065, Stress Ampl. = 0.05568 MPa
Typical Unload Secant Modulus = 38.17 MPa
Strain = 0.0005247, Stress = 0.05207 MPa
Typical Reload Secant Modulus = 34.32 MPa
Strain = 0.0006254, Stress = 0.05581 MPa
Typical Reload Secant Modulus = 35.5 MPa
Strain = 0.000625, Stress = 0.05773 MPa
LOOP-1 LOOP-2
LOOP-3 LOOP-4
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
108
Unload-reload shear moduli Gur (TXL) calculated from the unload-reload loops of triaxial
test curves are shown in Fig.4.10. Figure 4.10 shows overall trend of increase in shear
moduli with depth. The increase in shear moduli is due to the fact that the effective
consolidation pressure in triaxial tests (taken equal to overburden stress) increases with
depth. The Gu (TXL) and Gr (TXL) have been calculated from the unloading and reloading
portions of the unload-reload loops of triaxial curves and are shown in Figs.4.13, 4.14,
4.15 and 4.16.
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80
Gur(TXL), MPa
De
pth
, m
Fig. 4.10: Profile of Gur (TXL)
ML soil
CL-ML
soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
109
The profile of Gur(TXL) values (Fig. 4.10) shows the sharp increasing trend up to 6m depth
as compared with the values from 6m to 10m depth. The trend of increase is similar to
profile of CPT (Qc) in (Appendix-A) and SPT (N60) in (Appendix-B).
4.3.3 Comparison of Shear Moduli from PMT and Triaxial Tests
The variation of Gur (TXL) and Gur (PMT) with shear strain amplitude, for CL-ML and ML
soils, is shown in Figs. 4.11 & 4.12. The shear moduli normalized with p′ (effective
pressure at which the unloading in pressuremeter curve is started) have been shown in the
data in Figs. 4.11, 4.12, 4.13, 4.14, 4.15 and 4.16. The degradation of secant shear moduli
of triaxial and pressuremeter from unload and reload portions of unload-reload loops of
CL-ML and ML soils are shown in Figs. 4.13, 4.14, 4.15 and 4.16. The transformed strain
approach (Jardine, 1991) was used to convert the cavity strain of unload-reload loops of
PMT curves to an equivalent shear strain for the comparison of degradation of secant
shear moduli from unload and reload portions of the loops of PMT and triaxial tests.
0
100
200
300
400
0.01 0.1 1
Shear strain (, %
Gu
r/p
'
PMT TXL
Fig. 4.11: Gur (PMT) & Gur (TXL) vs. shear strain for CL-ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
110
0
100
200
300
400
0.01 0.1 1
Shear strain (), %
Gu
r/p
'
PMT TXL
Fig. 4.12: Gur (PMT) & Gur(TXL) vs. shear strain for ML soil
0
300
600
900
1200
0.001 0.01 0.1 1
Shear Strain (), %
Se
ca
nt
Sh
ea
r M
od
ulu
s (
Gu)/
p'
PMT TXL
Fig.4.13: Gu (PMT) & Gu (TXL) vs. shear strain for CL-ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
111
0
250
500
750
1000
0.001 0.01 0.1 1
Shear Strain (), %
Secan
t S
hear
Mo
du
lus (
Gr)
/p'
PMT TXL
Fig. 4.14: Gr (PMT) & Gr (TXL) vs. shear strain for CL-ML soil
0
300
600
900
1200
0.001 0.01 0.1 1
Shear Strain (), %
Secan
t S
hear
Mo
du
lus (
Gu)/
p'
PMT Series2
Fig.4.15: Gu (PMT) & Gu (TXL) vs. shear strain for ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
112
0
250
500
750
1000
0.001 0.01 0.1 1
Shear Strain(), %
Se
ca
nt
Sh
ea
r M
od
ulu
s (
Gr)
/p'
PMT TXL
Fig. 4.16: Gr (PMT) & Gr (TXL) vs. shear strain for ML soil
Figures 4.11 & 4.12 show that the Gur values of CL-ML and ML soils in pressuremeter
and triaxial tests decrease with increase in shear strain and also show that the
pressuremeter data values lie below triaxial curves (Jardine, 1991). The Gur values for the
pressuremeter and triaxial can be compared for the same shear strain values.
In Figs. 4.13 & 4.15, it is evident that the unload secant shear modulus Gu in
pressuremeter and triaxial (CIU and CID) tests decreases with increase in shear strain
during unloading (Jardine, 1991) in unload portion of the loop for CL-ML and ML soils.
The pressuremeter and triaxial data values are in close proximity with each other. The
closeness of these data values is more apparent in case of ML soils. The consistent values
of shear moduli have been observed in case of ML soils.
In Figs. 4.14 & 4.16, it is obvious that the reload secant shear modulus (Gr) determined
from reload portion of the unload-reload loop in pressuremeter and triaxial (CIU and
CID) tests decreases with increase in shear strain in CL-ML and ML soils. It is apparent
from the Figs. 4.14 & 4.16 that Gr from pressuremeter and triaxial tests strongly resemble
with each other. It also shows that the Gr values from pressuremeter and triaxial tests are
very consistent for both CL-ML and ML soils.
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
113
Secant shear moduli values degradation (Figs. 4.13, 4.14, 4.15 and 4.16) show that the
shear modulus is strain sensitive. More scatter in shear moduli values has been observed
at the strain lesser than 0.01%. Instead of determining single value of shear modulus (Gur)
from the unload-reload loop of the pressuremeter test, the secant moduli (unload and
reload) can be determined from the PMT loop for the corresponding strains. These moduli
can be used in geotechnical designs where specific strains are very important to be
considered for the selection of shear moduli.
4.4 CORRELATIONS OF PMT AND RESONANT COLUMN DATA
Resonant column typical test data in Fig.3.36 shows that there is increase in maximum
dynamic shear modulus (Gmax) with decrease in shear strain which is achieved by
increasing the effective stress ( p′) during four stages ( p′ = 0.1, 0.2, 0.3 and 0.4 MPa) of
the resonant column test. It is evident that after 4th
stage of the resonant column test, the
shear strain is increased which causes the decrease in shear modulus. The decrease in
shear modulus with increase in shear strain shows the degradation of shear modulus.
Figures 4.17 and 4.18 for CL-ML and ML soils respectively show that when the effective
stress is increased in the order of 0.1, 0.2, 0.3 and 0.4 MPa, the Gmax values also increase
accordingly. Hence four Gmax values obtained from this test can be used in design for the
relevant stress and strain levels. The different Gmax values at the same depth may be due
to the change in strata, density and initial moisture content of the soil samples.
The Gmax data from resonant column test for CL-ML and ML soils for effective stress of
0.1MPa was related with Gur determined from pressuremeter tests conducted up to 10m
depth. The relationships in Figs. 4.19 and 4.20 show the ratio Gur / Gmax = 0.4625 for CL-
ML soils and Gur / Gmax = 0.4906 for ML soils. These ratios are comparable with the ratio
Gur / Gmax = 0.2 to 0.6 (Hughes and Robertson, 1985; Bellotti et al. 1989). It is evident
from the Figs. 4.19 and 4.20 that if the pressuremeter test in CL-ML and ML soils is
conducted, the Gmax value can be evaluated. These relationships provide the cost effective
method of evaluation of Gmax as the resonant column test is very costly and time
consuming to be conducted. Hence by conducting the static test (pressuremeter test), the
dynamic shear modulus (Gmax) values can be determined by using the relationships shown
in Figs. 4.19 and 4.20.
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
114
0
20
40
60
80
100
120
140
0 0.1 0.2 0.3 0.4 0.5
Effective Stress, MPa
Gm
ax
(RC
), M
Pa
1m 1m 1m 2m 2m 2m 3m3m 3m
Fig. 4.17 Gmax(RC) vs. effective stress for CL-ML soils
0
30
60
90
120
150
180
210
0 0.1 0.2 0.3 0.4 0.5
Effective Stress, MPa
Gm
ax
(RC
), M
Pa
4m 4m 5m 5m 6m 7m 7m
8m 9m 10m 10m
Fig. 4.18: Gmax(RC) vs. effective stress for ML soils
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
115
Gmax(RC) = 2.1515Gur(PMT)
R2 = 0.8625
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Gur(PMT), MPa
Gm
ax(R
C), M
Pa
Fig. 4.19: Correlation of Gmax from resonant column and Gur from PMT for CL-ML soils.
Gmax(RC) = 2.0657Gur(PMT)
R2 = 0.9116
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60
Gur(PMT), MPa
Gm
ax(R
C), M
Pa
Fig. 4.20: Correlation of Gmax from resonant column and Gur from PMT for ML soils.
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
116
The correlations from figures 4.19 and 4.20 are given below:
)()max( 1515.2 PMTurRC GG (for CL-ML soil) (4.1)
)()max( 0657.2 PMTurRC GG (for ML soil) (4.2)
4.5 LIMIT PRESSURE
Limit pressures were determined from the cavity pressure vs cavity strain curves of
pressuremeter tests (Fig.4.21). The cavity pressure corresponding to 41% cavity strain
(proposed by Clarke, 1995) was interpreted as limit pressure from the PMT curves. The
limit pressures of non-cohesive ML soil (Fig. 4.22) match with the values given by
Briaud (1992) for sand.
0
200
400
600
800
1000
1200
1400
1600
1800
0 10 20 30 40 50
Cavity strain, %
Cavit
y p
ressu
re,
kP
a
Fig. 4.21: Determination of limit Pressure from PMT curve
Figure 4.22 presents profiles of limit pressures of CL-ML soil up to 3m and ML soil from
3 to 10m depth.
Limit pressure at 41% cavity strain = 1600 kPa
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
117
0
1
2
3
4
5
6
7
8
9
10
0 500 1000 1500 2000
PL(PMT), kPa
De
pth
,m
Fig. 4.22: Profiles of limit pressures
The profile of PL(PMT) (Fig. 4.22) shows almost similar trend as profile of CPT (Qc) in
(Appendix-A), SPT (N60) in (Appendix-B) and Gur(PMT) in Fig.4.7. The limit pressure
profile (Fig. 4.22) shows increase of limit pressure with depth as the overburden stress
increases with depth.
Gur(TXL) = 40.175PL(PMT)0.6659
R2 = 0.8032
0
5
10
15
20
25
30
35
0 0.2 0.4 0.6 0.8
PL(PMT), MPa
Gu
r(T
XL
), M
Pa
Fig.4.23: Correlation of PL(PMT) and Gur(TXL) for CL-ML soil.
CL-ML soil
ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
118
Gur(TXL) = 45.293PL(PMT)0.5461
R2 = 0.7715
0
10
20
30
40
50
60
70
0 0.5 1 1.5 2
PL(PMT), MPa
Gu
r(T
XL
), M
Pa
Fig.4.24: Correlation of PL(PMT) and Gur(TXL) for ML soil.
Figs. 4.23 & 4.24 show that there is a good relationship between PL(PMT) and Gur(TXL) both
in CL-ML and ML soils. Hence by conducting the PMT test in field, even without
unload-reload loops, the Gur values of laboratory triaxial tests i.e. Gur(TXL) can be assessed.
The cone tip resistance (Qc) from CPT data was related with limit pressure of PMT test
curves for CL-ML and ML soils as shown in Figs 4.25 and 4.26. The Qc values increase
with the increase in limit pressure both for CL-ML and ML soils.
Qc = 8.9928PL
R2 = 0.7589
0
1
2
3
4
5
6
7
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
PL, MPa
Qc, M
Pa
Fig. 4.25: Correlation between Qc from CPT and limit pressure from PMT for CL-ML
soils
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
119
Qc = 8.3614PL
R2 = 0.7309
0
2
4
6
8
10
12
14
16
0.0 0.5 1.0 1.5 2.0
PL, MPa
Qc,
MP
a
Fig. 4.26: Correlation between Qc from CPT and limit pressure from PMT for ML soils
The limit pressure from pressuremeter was related with SPT N60 values and the increase
in limit pressure has been observed with increases in N60 values as shown in Figs. 4.27
and 4.28. The proposed correlations in these Figures 4.27 and 4.28 are similar to the
correlation proposed by Yagiz et al. (2008) for medium to very stiff sandy silty clay.
PL(PMT) = 45.268N60 + 22.16
R2 = 0.9585
0
100
200
300
400
500
600
700
800
0 2 4 6 8 10 12 14 16
SPT N60 Value
PL
(P
MT
), k
Pa
Fig. 4.27: Correlation between PMT limit pressure and SPT N value for CL-ML soils
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
120
PL(PMT) = 63.364N60 + 31.628
R2 = 0.7042
0
300
600
900
1200
1500
1800
0 5 10 15 20 25 30
SPT N60 Value
PL
(P
MT
), k
Pa
Fig. 4.28: Correlation between PMT limit pressure and SPT N value for ML soils
The correlations from figures 4.23, 4.24, 4.25, 4.26, 4.27 and 4.28 are given as:
6659.0175.40 )()( PMTLTXLur PG (for CL-ML soil) (4.3)
5461.0293.45 )()( PMTLTXLur PG (for ML soil) (4.4)
LC PQ 9928.8 (for CL-ML soil) (4.5)
LC PQ 3614.8 (for ML soil) (4.6)
16.22268.45 60)( NP PMTL (for CL-ML soil) (4.7)
628.31364.63 60)( NP PMTL (for ML soil) (4.8)
4.6 IN-SITU HORIZONTAL STRESS (ho)
The in-situ horizontal stress (ho) up to 3m depth for CL-ML soil was determined by the
method given by Denby (1978) and Fahey and Randolph (1984) for clayey soils and the
in-situ stress was also determined by the inspection of lift-off point from the PMT curves
obtained by New Technique. The in-situ horizontal stress (ho), from 3m to 10m depth
for ML soil has been determined by the method given by Denby (1978) and Fahey and
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
121
Randolph (1984) for sandy soils. The analysis for determination of ho for ML soil is
shown in Fig. 4.29.
The method for the determination of ho for ML soil is shown in Fig. 4.29. The different
datum levels for strains have been selected and the data was plotted for ln(cavity
pressure) versus ln(current cavity strain). The plot which shows the maximum straight
portion was selected. The datum strain for this plot gives the cavity diameter for the
determination of in-situ horizontal stress. For clayey soils, the cavity pressure is plotted
against ln(cavity strain). The remaining method is same as for sandy soils.
4.0
4.4
4.8
5.2
5.6
6.0
-12 -10 -8 -6 -4 -2 0
ln (Current Cavity Strain)
ln (
Cavit
y P
ressu
re)
RDS=0.0163 RDS=0.0237 RDS=0.0326RDS=0.0349 RDS=0.0408 RDS=0.0434
Fig.4.29 The plots of loading portion of PMT curve at different datum strains at 4m
depth
Line selected
for ho
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
122
0
1
2
3
4
5
6
7
8
9
10
0 20 40 60 80 100
ho, kPa D
ep
th, m
Location-1 Location-2 Location-3 Location-4
Fig. 4.30 In-situ horizontal stress of CL-ML and ML soils
The profiles of (ho) for CL-ML and ML soils are shown in Fig. 4.30. The values of ho
for CL-ML soils up to 3m depth match with those given by Clarke (1995) for London
clay and also with those given by Lacasse et al. (1990) for medium stiff Haga clay. The
ho values of ML soil from 3 to 10m match with those given by Bruzzi et al. (1986) for
dense Po River sand.
4.6.1 Comparison of Traditional and New Techniques for ho
The insitu horizontal stress (ho) determined in boreholes drilled by traditional technique,
was interpreted from the pressuremeter test curves by Denby (1978) and Fahey and
Randolph (1984) method. The ho values determined by New Technique were compared
with those determined by Denby (1978) and Fahey and Randolph (1984) method. A
comparison of the two techniques is presented in Fig.4.31 which shows that ho values
determined from PMT curves by New Technique are higher than those determined from
traditional technique.
CL-ML soil
ML soil
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
123
Fig. 4.31: PMT test curves by traditional and new technique.
The insitu horizontal stress ho determined from traditional and new techniques have been
correlated and shown in Fig.4.32 up to 5m depth which show that ho values from new
technique are 1.1 times larger than traditional technique which may be due to the fact that
in new technique the soil is tested in relatively undisturbed condition as compared with
the traditional technique.
0
200
400
600
0 5 10 15 20 25 30 35 40 45 50Cavity Strain %
Cavit
y P
ressu
re, kP
a
3m depth --New technique3m depth--Traditional preboring technique
Lift-off pressure = 41 kPa
= In-situ Horizontal Stress
Traditional
technique
New technique
Insitu horizontal stress = 37 kPa
Fahey and Randolph, (1984)
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
124
ho(NT) = 1.0953ho(TT)
R2 = 0.8975
0
10
20
30
40
50
60
0 10 20 30 40 50 60
ho, kPa by Traditional Technique
h
o, k
Pa
by
Ne
w T
ec
hn
iqu
e
Fig. 4.32: ho from Traditional Technique (TT) and New Technique (NT)
The correlation from figure 4.32 is given as:
)()( 0953.1 TThoNTho (4.9)
4.7 SHEAR STRENGTH
The undrained shear strength (Su) was interpreted by the method given in Clarke (1997)
from the pressuremeter test curves obtained in holes drilled by New Technique.
Undrained shear strength (Su) values determined from PMT test curves by New
Technique were related with the Su determined from unconfined compression test (UCT)
up to 3m depth for CL-ML soils. The results in Fig. 4.33 show that most of the Su(PMT)
values are larger than those from Su(UCT).
CHAPTER-4 ANALYSIS AND DISCUSSION ON RESULTS
125
Su(UCT) = 0.8946Su(PMT)
R2 = 0.9226
0
20
40
60
80
100
120
0 20 40 60 80 100 120
Su(PMT), kPa
Su
(UC
T), k
Pa
Fig. 4.33: Correlation of Su(PMT) and Su(UCT).
The correlation from figure 4.33 is given as:
)()( 8946.0 PMTuUCTu SS (4.10)
4.8 SUMMARY
The mechanical drilling system (MDS) has proven the ability to drill nearly vertical and
constant diameter boreholes for the pressuremeter testing. The pressuremeter test curves
in the boreholes drilled by MDS show all the three phases of quality pressuremeter test
i.e. pushing of borehole wall to its original position, pseudo-elastic and plastic phases.
The drilling of boreholes by MDS is cost effective than hand auger and rotary rig.
Unload, reload and unload-reload shear moduli determined from unload-reload loops of
pressuremeter and triaxial tests were compared. The reload moduli are more consistent
than unload and unload-reload shear moduli. The degradation of the shear moduli both in
pressuremeter and triaxial tests shows the dependence of the shear moduli on strain.
Different correlations of geotechnical parameters determined from pressuremeter and
laboratory testing were developed so that the pressuremeter test can be used instead of
laboratory tests for the determination of precise and cost effective geotechnical
parameters for use in geotechnical design.
CHAPTER-5
126
CONCLUSIONS AND RECOMMENDATIONS
5.1 INTRODUCTION
The research was undertaken with the main objective to develop a simple mechanical
drilling system (MDS) to create a truly vertical hole of uniform diameter in order to
perform high quality prebored pressuremeter testing. After developing this system,
boreholes were drilled with hand auger and conventional rotary drilling rig for
comparison with the boreholes drilled through newly developed MDS.
In-situ testing comprising four sets was conducted in alluvial soils that classify as silty
clay (CL-ML) and silt (ML). Each set included two prebored pressuremeter (PMT)
points, one Electrical Cone Penetrometer (CPT), one Standard Penetration Test (SPT) and
one sampling borehole, each up to 10 m depth. The Prebored Pressuremeter testing was
conducted in boreholes drilled by the MDS. The laboratory tests were performed on
undisturbed and disturbed soil samples obtained from the sampling borehole. The
laboratory testing included triaxial (CU and CD) tests with unload-reload loops, resonant
column tests, direct shear tests, unconfined compression tests along with soil
classification tests.
The in-situ and laboratory testing data have been analyzed to check correlations between
them.
Based on the research work carried out as per the scope of work cited above, following
conclusions and recommendations are made:
5.2 CONCLUSIONS
a) The newly developed Mechanical Drilling System is simple and can be used with
confidence in alluvial soils for obtaining truly vertical and uniform diameter
boreholes up to 10 m depth. The verticality and uniform diameter of boreholes
obtained using the Mechanical Drilling System are better than the hand auger and
rotary rig boreholes (Figs. 3.9 & 3.10).
CHAPTER-5 CONCLUSIONS AND RECOMMENDATIONS
127
b) The Mechanical Drilling System is cost effective compared with the rotary rig (Table
4.1).
c) The prebored PMT curves can be obtained up to 40% cavity expansion by the use of
Mechanical Drilling System. This strain range is enough to study the three distinctive
deformation phases of soils usually obtained in quality prebored pressuremeter tests
i.e. stressing of borehole walls to natural position, pseudo-elastic (micro plastic) and
plastic (Figs. 4.2 & 4.3).
d) The unload-reload shear modulus (Gur) and unload shear modulus (Gu) determined
from the prebored PMT curves resemble reasonably with those from the triaxial test
(Figs. 4.11, 4.12, 4.13 & 4.15)
e) Reload secant shear moduli (Gr) obtained from the PMT test curves are more
consistent than other moduli when compared with those from triaxial test (Figs. 4.14
& 4.16).
f) The shear moduli from the prebored PMT were obtained in shear strain range from
0.0051% to 0.2329% and those from Triaxial in shear strain range from 0.003656% to
0.18764%. Hence shear strain range in both devices is reasonably comparable for
shear modulus evaluation (Figs. 4.11, 4.12, 4.13, 4.14, 4.15 & 4.16).
g) Good correlation has been observed between Gur from the pressuremeter test curve
and Gmax from the resonant column dynamic test data (Figs. 4.19 & 4.20). Hence Gmax
may be estimated from the pressuremeter test instead from costly and time consuming
resonant column test.
h) Good correlation obtained between limit pressure from the pressuremeter test and Gur
from the triaxial test makes it possible to determine Gur from the simple pressuremeter
test (Figs. 4.23 & 4.24).
i) Limit pressure from the pressuremeter shows good correlations with tip resistance
from the CPT soundings and SPT blows. (Figs. 4.25, 4.26, 4.27 & 4.28).
j) A new cost effective technique has been developed to estimate in-situ horizontal
stress more reliably using the prebored PMT (Fig. 4.32).
k) Undrained shear strength determined from the pressuremeter test curve shows good
correlation with that determined from the unconfined compression test (Fig. 4.33).
CHAPTER-5 CONCLUSIONS AND RECOMMENDATIONS
128
l) The correlations proposed between various geotechnical parameters are presented in
table 5.1:
Table 5.1: Correlations proposed:
Sr. No.
Parameters Proposed Correlation
1 Gmax(RC), Gur(PMT)
)()max( 1515.2 PMTurRC GG (for CL-ML soil)
where Gmax(RC) and Gur(PMT) are in units of MPa.
2 Gmax(RC), Gur(PMT) )()max( 0657.2 PMTurRC GG (for ML soil)
where Gmax(RC) and Gur(PMT) are in units of MPa.
3 Gur(TXL), PL(PMT) 6659.0175.40 )()( PMTLTXLur PG (for CL-ML soil)
where Gur(TXL) and PL(PMT) are in units of MPa.
4 Gur(TXL), PL(PMT) 5461.0293.45 )()( PMTLTXLur PG (for ML soil)
where Gur(TXL) and PL(PMT) are in units of MPa.
5 QC, PL
LC PQ 9928.8 (for CL-ML soil)
where QC and PL are in units of MPa.
6 QC, PL LC PQ 3614.8 (for ML soil)
where QC and PL are in units of MPa.
7 PL(PMT), N60
16.22268.45 60)( NP PMTL (for CL-ML soil)
where PL(PMT) is in units of kPa.
8 PL(PMT), N60 628.31364.63 60)( NP PMTL (for ML soil)
where PL(PMT) is in units of kPa.
9 Su(UCT), Su(PMT)
)()( 8946.0 PMTuUCTu SS (for CL-ML soil)
where Su(UCT) and Su(PMT) are in units of kPa.
CHAPTER-5 CONCLUSIONS AND RECOMMENDATIONS
129
5.3 RECOMMENDATIONS FOR FUTURE RESEARCH
In order to continue the present research, following recommendations are made:
a) The present research is confined to CL-ML and ML soils which may be extended to
sand.
b) In-situ horizontal stress determined by the new technique should be checked against
that determined using self-boring PMT technique above and below the GWT.
c) The Prebored PMT testing may be carried out below GWT in order to study pore
water pressure characteristics.
d) The Pressuremeter used in this research is capable to test stiff/medium dense soils. It
may be made more rigorous to test hard/very dense soils.
130
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136
APPENDIX-A
CPT PROFILES
137
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16
Cone Tip Resistance Qc, MPaD
ep
th,
m
Location 1
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14 16
Cone Tip Resistance Qc, MPa
Dep
th, m
Location 2
138
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14
Cone Tip Resistance Qc, MPaD
ep
th, m
Location 3
0
1
2
3
4
5
6
7
8
9
10
0 2 4 6 8 10 12 14
Cone Tip Resistance Qc, MPa
Dep
th, m
Location 4
139
0
1
2
3
4
5
6
7
8
9
10
0 100 200 300 400 500 600
Sleeve Friction (fs) kPa
Dep
th,
m
Location 1
0
1
2
3
4
5
6
7
8
9
10
0 100 200 300 400
Sleeve Friction (fs) kPa
De
pth
, m
Location 2
140
0
1
2
3
4
5
6
7
8
9
10
0 50 100 150 200 250 300 350
Sleeve Friction (fs) kPaD
ep
th,
m
Location 3
0
1
2
3
4
5
6
7
8
9
10
0 50 100 150 200 250 300 350 400
Sleeve Friction (fs) kPa
Dep
th, m
Location 4
141
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5Friction Ratio (Rf) %
Dep
th, m
Location 1
0
1
2
3
4
5
6
7
8
9
10
0 0.5 1 1.5 2 2.5 3 3.5 4
Friction Ratio (Rf) %
Dep
th, m
Location 2
142
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6
Friction Ratio (Rf) %D
ep
th
Location 3
0
1
2
3
4
5
6
7
8
9
10
0 1 2 3 4 5 6 7Friction Ratio (Rf) %
De
pth
, m
Location 4
143
APPENDIX-B
SPT PROFILES
144
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25
SPT Blows, N60
Dep
th,
m
Location 1
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30
SPT Blows, N60
De
pth
, m
Location 2
145
0123456789
10
0 5 10 15 20 25
SPT Blows, N60
De
pth
, m
Location 3
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25
SPT Blows, N60
Dep
th, m
Location 4
146
APPENDIX-C
RESONANT COLUMN TESTS
(G/Gmax and damping ratio)
147
0
0.2
0.4
0.6
0.8
1
0.0001 0.001 0.01 0.1 1
Shear strain, %
G/G
ma
x
1m 1m 1m 2m 2m 2m 3m 3m 3m 4m
4m 5m 5m 6m 7m 7m 8m 9m 10m 10m
0
5
10
15
0.0001 0.001 0.01 0.1 1
Shear strain, %
Dam
pin
g r
ati
o,
%
1m 1m 1m 2m 2m 2m 3m 3m 3m 4m
4m 5m 5m 6m 7m 7m 8m 9m 10m 10m