## Contents

Preface ix

Conversion factors xi

1 Introduction 1

1.1 Project description 2

1.2 Field data 6

1.3 Laboratory data 6

2 Soil formation and exploration 11

2.1 Rock weathering and soil formation 11

2.2 Residual and transported soils 12

2.2.1 Transported soils 12

2.2.2 Project analysis: soil origin 13

2.3 Soil mineralogy 14

2.4 Soil exploration 14

2.4.1 Desk study 14

2.4.2 Boreholes 15

2.4.3 Laboratory tests 16

2.5 Project analysis: field and laboratory data 17

2.5.1 Borehole logs and cross-section 17

2.5.2 Field work: dynamic cone penetration test 18

2.6 Review quiz 20

3 Soil constituents 23

3.1 Three phases in soil 23

3.2 Volumetric ratios 24

3.2.1 Void ratio 24

3.2.2 Relative density 24

3.2.3 Porosity 25

3.2.4 Degree of saturation 25

3.3 Mass ratios 26

3.3.1 Density 26

3.3.2 Unit weight 26

3.3.3 Water content 26

3.3.4 Specific gravity 27

3.4 More about soil constituents 27

3.5 Project analysis: soil constituents 28

3.6 Problems for practice 30

3.7 Review quiz 36

4 Soil classification 37

4.1 Size of soil fractions 37

4.2 Laboratory work: sieve test and analysis 37

4.3 Soil gradation 39

4.4 Clay fraction, clay minerals and clay properties 40

4.4.1 Atterberg limits 41

4.4.2 Laboratory work: Atterberg limits tests and analysis 42

4.4.3 The plasticity chart 43

4.5 Soil classification 43

4.6 Clay activity and liquidity index 46

4.7 Project analysis: soil classification 47

4.8 Problems for practice 49

4.9 Review quiz 51

5 Soil compaction 53

5.1 Compaction process 53

5.2 Laboratory work: compaction tests and analysis 54

5.3 Compaction in the field 55

5.4 Project analysis: soil compaction 56

5.5 Problems for practice 58

5.6 Review quiz 61

6 Stresses in soils 63

6.1 Stresses in soil mass 63

6.2 Effective stress and pore water pressure 64

6.2.1 Determination of pore water pressure in the field 65

6.2.2 Effective stress concept 65

6.2.3 Horizontal stresses 66

6.3 Excess pore water pressures 66

6.3.1 Water flow and hydraulic gradient 66

6.3.2 Upward seepage 67

6.3.3 Quick conditions 68

6.4 Project analysis: stresses and upward seepage 69

6.5 Problems for practice 71

6.6 Review quiz 75

7 Principles of water flow in soil 77

7.1 Soil permeability 77

7.2 Rate of water flow and velocity 78

7.3 Laboratory tests to determine the coefficient of permeability 78

7.3.1 Laboratory work: constant head test 78

7.3.2 Laboratory work: falling head test 80

7.4 Horizontal and vertical water flow in layered soil mass 80

7.5 Elevation, pressure and total heads 81

7.6 Principles of flow nets 82

7.6.1 Rate of seepage in flow nets 83

7.6.2 Pore water pressures in flow nets 84

7.6.3 Hydraulic uplift force under structures 84

7.7 Project analysis: flow net 85

7.8 Problems for practice 87

7.9 Review quiz 95

8 Mohr circle and stresses 97

8.1 Theoretical considerations 97

8.2 Mohr circle of stress 98

8.3 Determining stresses acting on plane 99

8.4 Pole method 100

8.5 Project analysis: Mohr circle and stresses in soil mass 101

8.6 Problems for practice 102

9 Principles of soil deformation 105

9.1 Soil deformation in practice 105

9.2 Laboratory tests to study soil strength 106

9.2.1 Unconfined compression test 106

9.2.2 Triaxial compression test 106

9.2.3 Drained versus undrained tests 106

9.3 Stress-strain characteristics of soil 107

9.3.1 Definition of strain 107

9.3.2 Pore water pressure coefficients 108

9.4 Project analysis: deformation of soft clay after load application 109

9.5 Problems for practice 110

9.6 Review quiz 112

10 Consolidation of soft soil 115

10.1 Process of consolidation 115

10.2 Types of settlements during consolidation 116

10.3 Soil consolidation in practice 117

10.4 One-dimensional consolidation 118

10.4.1 Laboratory consolidation tests 119

10.4.2 Calculations of total settlements 120

10.5 Project analysis: soil consolidation 120

10.5.1 Laboratory work: oedometer test 121

10.5.2 Total settlements after consolidation 122

10.6 Terzaghi’s theory of consolidation and its practical application 123

10.6.1 Coefficient of consolidation 125

10.6.2 Project analysis: time of consolidation 126

10.6.3 Project analysis: coefficient of permeability 127

10.7 Overconsolidation ratio 128

10.8 Problems for practice 128

10.9 Review quiz 133

11 Shear strength of soil 135

11.1 Shear strength of soil in practice 135

11.2 Shear strength of soil in the laboratory 135

11.3 Triaxial compression tests 137

11.3.1 Deviator stress and confining pressure 137

11.3.2 Analysis of triaxial compression tests 138

11.3.3 Effective stress conditions 138

11.3.4 Undrained triaxial compression tests 139

11.4 Stress path concept 139

11.5 Project analysis: shear strength 141

11.5.1 Laboratory work: shear box tests 141

11.5.2 Laboratory work: triaxial compression tests 142

11.5.3 Stress path analysis 144

11.6 Problems for practice 145

11.7 Slope stability analysis 152

11.7.1 Stability of infinite slopes 153

11.7.2 Limit equilibrium method 154

11.8 Project analysis: slope stability analysis 156

11.9 Review quiz 157

References 159

Index 161

## Preface

This book is written for students who would like to learn the fundamentals and practical

aspects of soil mechanics using a more hands-on approach than traditional textbooks. There

are several textbooks on soil mechanics on the market; however, most of these texts were

written many years ago using the traditional format of presentation. Students would then be

expected to rote learn and then regurgitate this information accordingly. However, our experience

as teachers suggests that this traditional format where the instructor provides students

with theoretical knowledge through a series of lectures and abstract textbook problems is not

sufficient to prepare students to tackle real geotechnical challenges. There is a real disjunct

between what students are taught in universities and what they are expected to do in practice

as engineering practitioners. It is not an uncommon situation that students are able to derive

complex equations in the classroom, but struggle in the workforce when faced with practical

engineering challenges.

This book employs a more engaging project-based approach to learning, which partially

simulates what practitioners do in real life. The project-based method, which has proven to be

a valid alternative to the traditional one, not only provides students with opportunities to better

understand the fundamentals of soil mechanics, but also allows them to gain experience

that is more practical and learn how to apply theory to practice. Our teaching experience

indicates that working on a practical project makes the learning process more relevant and

engaging. This book will appeal to the new generations of students who would like to have a

better idea of what to expect in their employment future. In this book, readers are presented

with a real-world challenge (in the form of a project-based assignment) similar to that which

they would encounter in engineering practice and they need to work-out solutions using the

relevant theoretical concepts that are briefly summarized in the book chapters. To complete

this project-based assignment, readers are required to undertake a series of major geotechnical

tasks including: a) interpretation of field and laboratory data, b) analysis of soil conditions,

c) identification of geotechnical problems at a construction site and d) assessment of

their effect on construction.

This book covers all significant topics in soil mechanics and slope stability analysis.

Each section is followed by several review questions that will reinforce the reader’s knowledge

and make the learning process more engaging. A few typical problems are discussed

at the end of chapters to help the reader develop problem-solving skills. Once the reader

has sufficient knowledge of soil properties and mechanics, they will be able to undertake a

project-based assignment to scaffold their learning. The assignment is based on real field and

laboratory data including boreholes and test results so that the reader can experience what

geotechnical engineering practice is like, identify with it personally and integrate it into their

own knowledge base. In addition, some problems will include open-ended questions, which

will encourage the reader to exercise their judgment and develop practical skills. To foster

the learning process, solutions to all questions will be provided and discussed.

We are grateful to all students of Soil Mechanics and Geotechnical engineering

courses at Griffith University for their constructive feedback in the past several years. We

are also grateful to Professor Arumugam Balasubramaniam for his continuous support and

encouragement.