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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)







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.


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.


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


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.


ALLUVIAL SOILS

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).


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


ALLUVIAL SOILS

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.


ALLUVIAL SOILS

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.


ALLUVIAL SOILS

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


ALLUVIAL SOILS

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.


ALLUVIAL SOILS

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


ALLUVIAL SOILS

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


ALLUVIAL SOILS

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


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)


ALLUVIAL SOILS

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


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)


ALLUVIAL SOILS

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


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.


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.


ALLUVIAL SOILS

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.


ALLUVIAL SOILS

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.


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


ALLUVIAL SOILS

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


ALLUVIAL SOILS

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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27

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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28

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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29

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.



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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


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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.


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32

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


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33

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.


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34

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 ′


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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


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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


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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37

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.


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38

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.


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39

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.


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40

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.


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41

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


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42

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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43

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


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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


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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


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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.


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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.


ALLUVIAL SOILS

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


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).


ALLUVIAL SOILS

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.


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


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


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


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



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



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



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



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:



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



62

Fig. 3.7 Setting of Inclinometer apparatus

Fig. 3.8 Inclinometer testing at site



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



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



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



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.



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



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



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



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



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.



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



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



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



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.



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



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.



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



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



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



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



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.



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.



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



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



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.



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



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



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



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.



91

Table 3.2 Summary of Soil Classification, NMC, Dry Density, Unconfined


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



92



Location

No Depth


density NMC Su(UCT)

Direct

Shear

Test


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



93



Location

No Depth


density NMC Su(UCT)

Direct

Shear

Test


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



94



Location

No Depth


density NMC Su(UCT)

Direct

Shear

Test


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



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



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


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.


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


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.


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



LOOP-2

P2 for min

min

P1 for max

max

Reloading Curve

Unloading Curve

1

2

3 4

5


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


Stress Amplitude = 0. 2119 MPa

LOOP-2

Gur = 47.35 MPa




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


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).


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


Strain = 0,000561, Stress = 0.03662 MPa

Typical Reload Secant Modulus = 21.0 MPa






Gur = 20.0166 MPa

Strain Ampl= 0.00072 , Stress Ampl = 0.04322 MPa







LOOP-1 LOOP-2

LOOP-3 LOOP-4


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



Gur = 29.76 MPa


Gur = 32.30 MPa










Gur = 32.95 MPa








LOOP-1 LOOP-2

LOOP-3 LOOP-4


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


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


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


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


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.


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.


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


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.


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


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


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


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


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


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


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


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)


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).


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).


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.


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


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


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

Documents

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