Foundation Engineering for Expansive Soils
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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
List of Symbols
Ac clay activity B width of footing B slope of matric suction vs water content curve c cohesion of soil C molar concentration Cc compression index CDA "Department of Army" heave index CH heave index Ch suction compression index Cm matric suction index Cp peak cohesion Cr residual cohesion Cs swelling index Ct compression index with respect to net normal stress Cw CLOD index C(?) correction function d distance between particles d pier shaft diameter D constrained modulus of soil D0 depth of nonexpansive fill e void ratio e base of natural logarithm, 2.71828 e0 initial void ratio Es Young's modulus of the soil EA Young's modulus of the soil in units of bars f lateral restraint factor fs anchorage skin friction fu uplift skin friction Ft nodal force tangent to pier Ft maximum interior tensile force g gravitational acceleration Gs specific gravity of solids h pressure head hd displacement pressure head hm matric suction head ho osmotic pressure head H thickness of a layer of soil ?H change in thickness of that layer due to heave Ht total hydraulic head i hydraulic head gradient Ipt instability index Iss shrink swell index k spring constant in APEX Ka active earth pressure K(h) coefficient of unsaturated hydraulic conductivity K0 coefficient of earth pressure at rest Kp passive earth pressure Ks coefficient of permeability L length of pier Lreqd required pier length LL liquid limit ?L/?LD linear strain relative to dry dimensions m molality m factor for swelling pressure correlation n porosity of the soil pa active earth pressure pF unit for soil suction p0 equivalent fluid pressure pp passive earth pressure P partial pressure of pore water vapor P load per linear dimension P footing load P/P0 relative humidity Pdl dead load on footing PI plasticity index PL plastic limit Pmax maximum tensile force P0 saturation pressure of water vapor over a flat surface of pure water at the same temperature P0 total load due to earth pressure q flow rate of water q distributed load qa allowable bearing pressure qu unconfined compressive strength qm mean rate of infiltration at the ground surface r radius r2 correlation coefficient rw sources or sinks of water R universal gas constant R resistance force RF risk factor RFw weighted risk factor Rp pullout capacity of helical bearing plate s coefficient for load effect on heave S degree of saturation %SP percent of swelling pressure that is applied by the total applied stress on the soil T absolute temperature Ts surface tension ua pore air pressure (ua)d displacement air entry pressure uw pore water pressure U total uplift force Ut nodal displacement tangent to pier V molar volume of a solution V total volume of soil ?V/V volumetric strain Vw volume of water in an element of soil w gravimetric water content waev air entry gravimetric water content wu gravimetric water content corresponding to a suction of 1 kPa we weight of sample at equilibrium ws weight of oven-dry sample ymax differential soil movement ys net ground surface movement z depth z elevation head z soil layer thickness zA depth of active zone zAD depth of design active zone zp depth of potential heave zs zone of seasonal moisture fluctuation zw zone (depth) of wetting zwt height above the water table ?z thickness of soil layer a compressibility factor a soil to pier adhesion factor a drainage slope a1 coefficient of uplift between the pier and the soil a2 coefficient of anchorage between the pier and the soil ß contact angle with tube ß reduction factor for expansive earth pressure ? unit weight of soil ?d dry density of...
