JOHN D. NELSON, has over 50 years of geotechnical engineering experience with emphasis in expansive soils.??He is Professor Emeritus of Civil Engineering at Colorado State University, and Principal Engineer at Engineering Analytics, Inc.

KUO CHIEH CHAO, has over 20 years of geotechnical experience in foundation design and construction on expansive soils. He is Vice President of Engineering Analytics, Inc. and Adjunct Professor at Colorado State University.

DANIEL D. OVERTON, has over 30 years of geotechnical engineering experience including foundation design for expansive soils. He is President of Engineering Analytics, Inc. and a Faculty Affiliate at Colorado State University.

ERIK J. NELSON, has over 30 years of experience in geotechnical engineering, foundation design, and forensic investigations for expansive soils. He is Vice President at Engineering Analytics, Inc.

Preface xv

List of Symbols xix

List of Abbreviations xxv

1. INTRODUCTION 1

1.1 Purpose 2

1.2 Organization 2

1.3 Terminology 4

References 7

2. NATURE OF EXPANSIVE SOILS 9

2.1 Microscale Aspects of Expansive Soil Behavior 9

2.1.1 The Clay Particle 10

2.1.2 Adsorbed Cations and Cation Hydration 15

2.1.3 The Clay Micelle 17

2.1.4 Crystalline and Osmotic Expansion 19

2.1.5 Effect of Mineralogy on Plasticity of Soil 21

2.1.6 Effect of Mineralogy on Expansion Potential 22

2.1.7 Effect of Type of Cation on Expansion Potential 22

2.2 Macroscale Aspects of Expansive Soil Behavior 24

2.2.1 Development of Natural Soil Deposits 24

2.2.2 Effect of Plasticity on Expansion Potential 26

2.2.3 Effect of Soil Structure, Water Content, and Density on Expansion Potential 27

2.3 Identification of Expansive Soils 30

2.3.1 Methods Based on Physical Properties 30

2.3.2 Mineralogical Methods 36

2.3.3 Chemical Methods 37

2.3.4 Comments on Identification Methods 39

2.4 Characteristics of Expansive Soil Profiles 40

2.4.1 Geographic Distribution of Expansive Soils 40

2.4.2 Expansive Soil Profiles 40

References 53

3. SITE INVESTIGATION 59

3.1 Program of Exploration 59

3.1.1 Reconnaissance Investigation 60

3.1.2 Preliminary Investigation 60

3.1.3 Design-Level Investigation 61

3.2 Forensic Investigation 68

References 72

4. SOIL SUCTION 74

4.1 Soil Suction Components 74

4.1.1 Matric Suction 76

4.1.2 Osmotic Suction 80

4.1.3 Total Suction 82

4.2 Soil Water Characteristic Curve 82

4.2.1 Mathematical Expressions for SWCC 84

4.2.2 Soil Water Characteristic Curves for Expansive Soils 86

4.2.3 Influence of Stress State on Soil Water Characteristic Relationships 89

4.2.4 Effect of Suction on Groundwater Profiles 89

4.3 Measurement of Matric Suction 90

4.3.1 Tensiometers 92

4.3.2 Axis Translation Technique 94

4.3.3 Filter Paper Method for Matric Suction 98

4.3.4 Thermal Conductivity Sensors 103

4.3.5 Electrical Resistance Sensors 104

4.4 Measurement of Osmotic Suction 105

4.4.1 Osmotic Tensiometers 105

4.4.2 Pore Fluid Extraction Technique 106

4.5 Measurement of Total Suction 107

4.5.1 Psychrometers 109

4.5.2 Filter Paper Method for Total Suction 110

References 114

5. STATE OF STRESS AND CONSTITUTIVE RELATIONSHIPS 119

5.1 State of Stress and Stress State Variables 119

5.2 Stress–Volume Relationships 124

5.3 Stress–Water Relationships 125

References 126

6. OEDOMETER TESTING 127

6.1 Consolidation-Swell and Constant Volume Tests 129

6.2 Correction of Oedometer Test Data 132

6.2.1 Correction for Oedometer Compressibility 133

6.2.2 Correction for Specimen Disturbance in the CV Test 137

6.2.3 Effect of the Corrections on Expansion Properties 138

6.3 Relationship Between CS and CV Swelling Pressures (the m Method) 140

6.4 Factors Influencing Oedometer Test Results 144

6.4.1 Initial Stress State Conditions 145

6.4.2 Soil Fatigue 146

6.4.3 Initial Consolidation of Sample 146

6.4.4 Time and Method of Inundation 147

6.4.5 Storage of Samples 148

6.4.6 Competency of Laboratory Personnel 149

References 149

7. WATER MIGRATION IN EXPANSIVE SOILS 152

7.1 Water Flow in Unsaturated Soils 153

7.1.1 Darcy’s Law for Unsaturated Soils 153

7.1.2 Water Mass Balance Equation 154

7.1.3 Vertical Seepage in Unsaturated Soil 155

7.1.4 Flow through Fractured Rocks and Bedding Planes 158

7.2 Depth and Degree of Wetting 162

7.2.1 Depth of Wetting 162

7.2.2 Degree of Wetting 163

7.2.3 Perched Water Tables in Layered Strata 164

7.2.4 Wetting Profiles 165

7.3 Determination of Final Water Content Profiles for Design 167

7.3.1 Hand Calculation of Final Water Contents for Design 168

7.3.2 Computer Modeling of Water Migration 170

7.4 Challenges in Water Migration Modeling for Expansive Soils 177

References 178

8. COMPUTATION OF PREDICTED HEAVE 182

8.1 Oedometer Methods 183

8.1.1 The Heave Equation 184

8.1.2 Computation of Free-Field Heave 186

8.1.3 Computation of Heave under an Applied Load 195

8.1.4 Computation of Design Heave 195

8.1.5 Discussion of Earlier Oedometer Methods Proposed to Compute Heave 201

8.1.6 Comments on the Heave Index 204

8.2 Soil Suction Methods 204

8.2.1 McKeen (1992) 205

8.2.2 Department of the Army (1983) 211

8.2.3 Hamberg and Nelson (1984) 212

8.2.4 Lytton (1994) 213

8.3 Empirical Methods 214

8.4 Progression of Heave with Time 214

8.4.1 Hyperbolic Equation 214

8.4.2 Use of Water Migration Modeling to Analyze Rate of Heave 221

8.5 Free-Field Surface Movement for Shrink–Swell Soils 222

8.6 Discussion of Heave Prediction 223

References 224

9. GENERAL CONSIDERATIONS FOR FOUNDATION AND FLOOR DESIGN 227

9.1 Risk and Life Cycle Costs 230

9.1.1 Classification of Expansion Potential 230

9.1.2 Risk Factor 234

9.2 Foundation Alternatives 243

9.3 Factors Influencing Design of Structures on Expansive Soils 243

9.3.1 Tolerable Foundation Movement 243

9.3.2 Design Life 251

9.3.3 Design Active Zone and Degree of Wetting 252

9.3.4 Site Grading 252

9.4 Remedial Measures 253

References 255

10. SOIL TREATMENT AND MOISTURE CONTROL 258

10.1 Overexcavation and Replacement 259

10.2 Prewetting Method 264

10.3 Chemical Admixtures 267

10.3.1 Lime Treatment 267

10.3.2 Cement Treatment 273

10.3.3 Fly Ash Treatment 274

10.3.4 Chemical Injection 274

10.4 Moisture Control Alternatives 275

10.4.1 Moisture Barriers 276

10.4.2 Subsurface Drains 281

10.4.3 Surface Grading and Drainage 283

10.5 Summary of Soil Treatment Methods 289

References 290

11. DESIGN METHODS FOR SHALLOW FOUNDATIONS 295

11.1 Spread Footing Foundations 295

11.1.1 Computation of Footing Heave 297

11.1.2 Spread Footing Design Examples 299

11.2 Stiffened Slab Foundations 308

11.2.1 Edge Heave and Center Heave 308

11.2.2 Differential Heave 311

11.3 Remedial Measures for Shallow Foundations 314

11.3.1 Footing Foundations 314

11.3.2 Stiffened Slab-on-Grade 317

11.3.3 Other Methods 318

References 318

12. DESIGN METHODS FOR DEEP FOUNDATIONS 320

12.1 Pier and Grade Beam Foundation 320

12.1.1 Design Methods 324

12.1.2 Load-Bearing Capacity 334

12.2 Patented Piers 335

12.2.1 Helical Piles 335

12.2.2 Micropiles 337

12.2.3 Push Piers 340

12.3 Deep Foundation Design Examples 342

12.3.1 Rigid Pier Design Example 342

12.3.2 APEX Design Example 345

12.3.3 Helical Pile Design Example 348

12.4 Remedial Measures for Deep Foundations 348

12.4.1 Pier and Grade Beam Foundation 349

12.4.2 Underpinning 349

References 350

13. FLOORS AND EXTERIOR FLATWORK 351

13.1 Slabs-on-Grade 351

13.2 Stiffened Slabs 356

13.3 Structural Floors 357

13.4 Exterior Slabs and Flatwork 358

13.5 Remediation Techniques 359

13.5.1 Structural Floor Systems 361

13.5.2 Moisture Control 361

13.5.3 Chemical Injection 361

13.5.4 Isolation of the Slab 361

13.5.5 Exterior Slabs 362

References 362

14. LATERAL PRESSURE ON EARTH RETAINING STRUCTURES 363

14.1 Computation of Lateral Pressure from Expansive Soils 363

14.2 Testing for Measuring Lateral Swelling Pressure 365

14.3 Reduction of Lateral Swelling Pressure 366

14.4 Design for Lateral Earth Pressure 367

References 370

Index 373

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