SOIL MECHANICS FUNDAMENTALS Muni Budhu

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SOIL MECHANICS FUNDAMENTALS Muni Budhu

Contents

About the Author xi
Other Books by this Author xiii
Preface xv
Acknowledgments xix
Notes for Students and Instructors xxi
Notation, Abbreviations, Unit Notation, and Conversion Factors xxv
1 Composition and Particle Sizes of Soils 1
1.1 Introduction 1
1.2 Definitions of Key Terms 1
1.3 Composition of Soils 2
1.3.1 Soil formation 2
1.3.2 Soil types 2
1.3.3 Soil minerals 3
1.3.4 Surface forces and adsorbed water 5
1.3.5 Soil fabric 6
1.4 Determination of Particle Size 7
1.4.1 Particle size of coarse-grained soils 7
1.4.2 Particle size of fine-grained soils 9
1.5 Characterization of Soils Based on Particle Size 10
1.6 Comparison of Coarse-Grained and Fine-Grained Soils for Engineering Use 18
1.7 Summary 19
Exercises 19
2 Phase Relationships, Physical Soil States, and Soil Classification 23
2.1 Introduction 23
2.2 Definitions of Key Terms 23
2.3 Phase Relationships 24
2.4 Physical States and Index Parameters of Fine-Grained Soils 36
2.5 Determination of the Liquid, Plastic, and Shrinkage Limits 40
2.5.1 Casagrande’s cup method: ASTM D 4318 40
2.5.2 Plastic limit test: ASTM D 4318 41
2.5.3 Shrinkage limit: ASTM D 427 and D 4943 42
2.6 Soil Classification Schemes 45
2.6.1 American Society for Testing and Materials and the Unified Soil
Classification System (ASTM-USCS) 45
2.6.2 AASHTO soil classification system 45
2.6.3 Plasticity chart 49
2.7 Engineering Use Chart 50
2.8 Summary 54
2.8.1 Practical examples 54
Exercises 57
3 Soils Investigation 63
3.1 Introduction 63
3.2 Definitions of Key Terms 64
3.3 Purposes of a Soils Investigation 64
3.4 Phases of a Soils Investigation 65
3.5 Soils Exploration Program 66
3.5.1 Soils exploration methods 67
3.5.1.1 Geophysical methods 67
3.5.1.2 Destructive methods 71
3.5.2 Soil identification in the field 72
3.5.3 Number and depths of boreholes 75
3.5.4 Soil sampling 76
3.5.5 Groundwater conditions 78
3.5.6 Types of in situ or field tests 79
3.5.6.1 Vane shear test (VST): ASTM D 2573 80
3.5.6.2 Standard penetration test (SPT): ASTM D 1586 81
3.5.6.3 Cone penetrometer test (CPT): ASTM D 5778 87
3.5.6.4 Pressuremeter: ASTM D 4719-87 90
3.5.6.5 Flat plate dilatometer (DMT) 90
3.5.7 Soils laboratory tests 92
3.5.8 Types of laboratory tests 92
3.6 Soils Report 93
3.7 Summary 95
Exercises 96
4 One- and Two-Dimensional Flows of Water Through Soils 99
4.1 Introduction 99
4.2 Definitions of Key Terms 99
4.3 One-Dimensional Flow of Water Through Saturated Soils 100
4.4 Flow of Water Through Unsaturated Soils 103
4.5 Empirical Relationship for kz 103
4.6 Flow Parallel to Soil Layers 105
4.7 Flow Normal to Soil Layers 106
4.8 Equivalent Hydraulic Conductivity 106
4.9 Laboratory Determination of Hydraulic Conductivity 108
4.9.1 Constant-head test 108
4.9.2 Falling-head test 109
4.10 Two-Dimensional Flow of Water Through Soils 112
4.11 Flownet Sketching 114
4.11.1 Criteria for sketching flownets 115
4.11.2 Flownet for isotropic soils 116
4.12 Interpretation of Flownet 116
4.12.1 Flow rate 116
4.12.2 Hydraulic gradient 117
4.12.3 Critical hydraulic gradient 117
4.12.4 Porewater pressure distribution 118
4.12.5 Uplift forces 118
4.13 Summary 119
4.13.1 Practical examples 119
Exercises 123
5 Soil Compaction 127
5.1 Introduction 127
5.2 Definition of Key Terms 127
5.3 Benefits of Soil Compaction 128
5.4 Theoretical Maximum Dry Unit Weight 128
5.5 Proctor Compaction Test: ASTM D 698 and ASTM D 1557 128
5.6 Interpretation of Proctor Test Results 131
5.7 Field Compaction 137
5.8 Compaction Quality Control 139
5.8.1 Sand cone: ASTM D 1556 139
5.8.2 Balloon test: ASTM D 2167 141
5.8.3 Nuclear density meter: ASTM D 2922 and ASTM D 5195 142
5.8.4 Comparisons among the three popular compaction quality
control tests 142
5.9 Summary 143
5.9.1 Practical example 143
Exercises 145
6 Stresses from Surface Loads and the Principle of Effective Stress 149
6.1 Introduction 149
6.2 Definition of Key Terms 149
6.3 Vertical Stress Increase in Soils from Surface Loads 150
6.3.1 Regular shaped surface loads on a semi-infinite half-space 150
6.3.2 How to use the charts 155
6.3.3 Infinite loads 156
6.3.4 Vertical stress below arbitrarily shaped areas 157
6.4 Total and Effective Stresses 166
6.4.1 The principle of effective stress 166
6.4.2 Total and effective stresses due to geostatic stress fields 167
6.4.3 Effects of capillarity 168
6.4.4 Effects of seepage 169
6.5 Lateral Earth Pressure at Rest 177
6.6 Field Monitoring of Soil Stresses 178
6.7 Summary 179
6.7.1 Practical example 179
Exercises 181
7 Soil Settlement 187
7.1 Introduction 187
7.2 Definitions of Key Terms 187
7.3 Basic Concept 188
7.4 Settlement of Free-Draining Coarse-Grained Soils 191
7.5 Settlement of Non–Free-Draining Soils 192
7.6 The One-Dimensional Consolidation Test 193
7.6.1 Drainage path 195
7.6.2 Instantaneous load 195
7.6.3 Consolidation under a constant load: primary consolidation 196
7.6.4 Effective stress changes 196
7.6.5 Effects of loading history 198
7.6.6 Effects of soil unit weight or soil density 198
7.6.7 Determination of void ratio at the end of a loading step 200
7.6.8 Determination of compression and recompression indexes 200
7.6.9 Determination of the modulus of volume change 201
7.6.10 Determination of the coefficient of consolidation 202
7.6.10.1 Root time method (square root time method) 203
7.6.10.2 Log time method 204
7.6.11 Determination of the past maximum vertical effective stress 205
7.6.11.1 Casagrande’s method 205
7.6.11.2 Brazilian method 206
7.6.11.3 Strain energy method 206
7.6.12 Determination of the secondary compression index 208
7.7 Relationship between Laboratory and Field Consolidation 216
7.8 Calculation of Primary Consolidation Settlement 218
7.8.1 Effects of unloading/reloading of a soil sample taken
from the field 218
7.8.2 Primary consolidation settlement of normally consolidated
fine-grained soils 219
7.8.3 Primary consolidation settlement of overconsolidated
fine-grained soils 219
7.8.4 Procedure to calculate primary consolidation settlement 220
7.9 Secondary Compression 221
7.10 Settlement of Thick Soil Layers 221
7.11 One-Dimensional Consolidation Theory 224
7.12 Typical Values of Consolidation Settlement Parameters and Empirical
Relationships 226
7.13 Monitoring Soil Settlement 227
7.14 Summary 228
7.14.1 Practical example 228
Exercises 232
8 Soil Strength 239
8.1 Introduction 239
8.2 Definitions of Key Terms 239
8.3 Basic Concept 240
8.4 Typical Response of Soils to Shearing Forces 240
8.4.1 Effects of increasing the normal effective stress 242
8.4.2 Effects of overconsolidation ratio, relative density,
and unit weight ratio 243
8.4.3 Effects of drainage of excess porewater pressure 245
8.4.4 Effects of cohesion 246
8.4.5 Effects of soil tension and saturation 247
8.4.6 Effects of cementation 248
8.5 Three Models for Interpreting the Shear Strength of Soils 249
8.5.1 Coulomb’s failure criterion 250
8.5.2 Mohr–Coulomb failure criterion 251
8.5.2.1 Saturated, uncemented soils at critical state (Figure 8.9) 252
8.5.2.2 Saturated, uncemented soils at peak state 252
8.5.2.3 Unsaturated, cemented, cohesive soils (Figure 8.10) 252
8.5.3 Tresca’s failure criterion 254
8.6 Factors Affecting the Shear Strength Parameters 256
8.7 Laboratory Tests to Determine Shear Strength Parameters 258
8.7.1 A simple test to determine the critical state friction angle of
clean coarse-grained soils 258
8.7.2 Shear box or direct shear test ASTM D 3080 258
8.7.3 Conventional triaxial apparatus 268
8.7.4 Direct simple shear 278
8.8 Specifying Laboratory Strength Tests 279
8.9 Estimating Soil Parameters from in Situ (Field) Tests 280
8.9.1 Vane shear test (VST): ASTM D 2573 280
8.9.2 Standard penetration test (SPT)): ASTM D 1586 281
8.9.3 Cone penetrometer test (CPT): ASTM D 5778 282
8.10 Some Empirical and Theoretical Relationships for Shear
Strength Parameters 283
8.11 Summary 284
8.11.1 Practical examples 284
Exercises 290
Appendix A: Derivation of the One-Dimensional Consolidation Theory 295
Appendix B: Mohr’s Circle for Finding Stress States 299
Appendix C: Frequently Used Tables of Soil Parameters and Correlations 301
Appendix D: Collection of Equations 313
References 325
Index 329

Preface

GOAL AND MOTIVATION

My intent in writing this textbook is to present accessible, clear, concise, and contemporary
course content for a first course in soil mechanics to meet the needs of undergraduates not
only in civil engineering but also in construction, mining, geological engineering, and related
disciplines.
However, this textbook is not meant to be an engineering design manual nor a cookbook.
It is structured to provide the user with a learning outcome that is a solid foundation on
key soil mechanics principles for application in a later foundation engineering course and
in engineering practice.
By studying with this textbook, students will acquire a contemporary understanding of
the physical and mechanical properties of soils. They will be engaged in the presentation of
these properties, in discussions and guidance on the fundamentals of soil mechanics. They
will attain the problem-solving skills and background knowledge that will prepare them to
think critically, make good decisions, and engage in lifelong learning.

PREREQUISITES

Students using this textbook are expected to have some background knowledge in Geology,
Engineering Mechanics (Statics), and Mechanics of Materials.

UNITS

The primary unit of measure used in this textbook is the US customary system of units.
However, ASTM standards require certain tests, for example, for particle sizes of soils, to
be conducted using SI units (International System of units). Therefore, wherever necessary,
SI units are used. An SI version of this textbook is also available.

HALLMARK FEATURES

Contemporary methods: The text presents, discusses, and demonstrates contemporary ideas
and methods of interpreting the physical and mechanical properties of soils that students
will encounter as practicing engineers. In order to strike a balance between theory and
practical applications for an introductory course in soil mechanics, the mechanics is kept to
a minimum so that students can appreciate the background, assumptions, and limitations
of the theories in use in the field.
The implications of the key ideas are discussed to provide students with an understanding
of the context for the applications of these ideas.
A modern explanation of soil behavior is presented particularly in soil settlement and soil
strength. These are foremost topics in the practice of geotechnical engineering. Onedimensional
consolidation is presented in the context of soil settlement rather than
as a separate topic (Chapter 7). The shear strength of soils is presented using contemporary
thinking and approach. In particular, three popular failure criteria—Coulomb,
Mohr-Coulomb, and Tresca—are discussed with regard to their applications and limitations.
Students will be able to understand how to use these criteria to properly interpret
soil test results and understand the differences between drained and undrained shear
strength.
Some common applications of soil mechanics principles are presented to introduce students
to and to inform them on the practical importance of studying soil mechanics.
Pedagogy and design directed by modern learning theory: The content and presentation of
the chapters are informed by modern theories of how students learn, especially with regard
to metacognition.
Learning outcomes listed at the beginning of each chapter inform students what knowledge
and skills they are expected to gain from the chapter. These form the bases for the problems
at the end of each chapter. By measuring students’ performance on the problems, an
instructor can evaluate whether the learning outcomes have been satisfied.
Definitions of key terms at the beginning of each chapter define key terms and variables that
will be used in the chapter.
Key points summaries throughout each chapter emphasize for students the most important
points in the material they have just read.
Practical examples at the end of some chapters give students an opportunity to see how the
prior and current principles are integrated to solve “real world type” problems. The students
will learn how to find solutions for a “system” rather than a solution for a “component”
of the system.
Consistent problem-solving strategy: Students generally have difficulty in translating a word
problem into the steps and equations they need to use to solve it. They typically can’t read
a problem and understand what they need to do to solve it. This text provides and models
consistent strategies to help students approach, analyze, and solve any problem. Example
problems are solved by first developing a strategy and then stepping through the solution,
identifying equations, and checking whether the results are reasonable as appropriate.
Three categories—conceptual understanding, problem solving, and critical thinking and
decision making—of problems are delineated at the end of the chapter to assess students’
knowledge mastery. These are not strict categories. In fact, the skills required in each category
are intermixed. Problems within the conceptual understanding category are intended to
assess understanding of key concepts and may contain problems to engage lateral thinking.
It is expected that the instructor may add additional problems as needed. Problems within
the problem-solving category are intended to assess problem-solving skills and procedural
fluency in the applications of the concepts and principles in the chapter. Problems within
the critical thinking and decision-making category are intended to assess the student’s
analytical skills, lateral thinking, and ability to make good decisions. These problems have
practical biases and require understanding of the fundamentals. Engineers are required to
make decisions, often with limited data. Practical experience is a key contributor to good
decisions. Because students will invariably not have the practical experience, they will have
to use the fundamentals of soil mechanics, typical ranges of values for soils, and their cognitive
skills to address problems within the critical thinking and decision-making category.
The instructors can include additional materials to help the students develop critical thinking
and decision-making skills.
Knowledge mastery assessment software. This textbook is integrated with YourLabs™
Knowledge Evaluation System (KES) (www.yourlabs.com). This system automatically grades
students’ solutions to the end of chapter problems. It allows students to answer the problems
anywhere on any mobile device (smartphone, iPad, etc.) or any desktop computing device
(PC, MAC, etc.). After answering each question in an assignment set by the instructor on
KES, the student’s answer (or answers to multi-parts problems) is compared to the correct
answer (or answers in multi-parts problems) and scored. The student must step through the
solution for each problem and answer preset queries to assess concept understanding, critical
thinking, problem-solving skills, and procedural fluency. KES then analyzes the feedback
from students immediately after submitting their responses and displays the analytics to the
students and the instructor. The analytics inform the instructor what the students know and
don’t know, at what steps, and the types of mistakes made during problem solving. The
instructor can re-teach what the students did not know in a timely manner and identify
at-risks students. The analytics are also displayed to the student to self-reflect on his/her
performance and take corrective action. Relevant instructional materials are linked to each
problem, so the student can self-learn the materials either before or upon completion of the
problem. Instructors can modify the questions and assets (links or embedded videos, images,
customized instructional materials, etc.) and, at each step of the solution, add or delete solution
steps or create a customized question. Each problem can be tagged with any standard
required by academic or professional organizations. The analytics as well as students’ scores
are aggregated from the problem to assignment and to class or course levels.