Unsaturated Soil Mechanics in Geotechnical Practice

Unsaturated Soil Mechanics
in Geotechnical Practice......Page 4
Contents......Page 6
Preface......Page 20
Acknowledgements......Page 22
About the author......Page 24
Scales, plotting conventions for graphs and reference lists......Page 26
Reference......Page 27
List of References......Page 28
List of abbreviations and mathematical symbols......Page 30
1.1 Historical progress in unsaturated soil mechanics literature: Karl Terzaghi's four books......Page 36
1.2 Meetings, documents and books that were critical in establishing unsaturated soil mechanics as a sub-discipline of soil mechanics......Page 45
1.2.1 Matrix suction......Page 47
1.2.2 Solute (or osmotic) suction......Page 48
1.3 Progress in disseminating knowledge of unsaturated soil mechanics via basic soil mechanics text books......Page 53
1.4 The special problem of unsaturated soils......Page 60
References......Page 61
Plate......Page 63
2.1 The definition of an unsaturated soil......Page 64
2.2 Interaction of pore air and pore water......Page 67
2.3 The use of elevated pore-air pressures in the measurement of pore-water pressures (the axis translation technique) (Bishop & Blight, 1963)......Page 70
2.4 The suction-water content curve (SWCC) (Blight, 2007)......Page 73
2.4.1 Hysteresis in a saturated soil......Page 74
2.4.2 Hysteresis in drying soils......Page 75
2.4.3 Direct comparison between a consolidation curve and a SWCC......Page 77
2.4.4 Hysteresis in compacted soils and the effect of particle size distribution......Page 78
2.4.5 SWCCs extending to very dry soils, or high suctions......Page 79
2.4.6 Empirical expressions for predicting SWCCs......Page 81
2.4.7 The effect of soil variability on SWCCs and SWCCs measured by means of in situ tests......Page 83
2.5 The characteristics of the effective stress equation for unsaturated soils (Bishop & Blight, 1963)......Page 84
2.5.1 Evaluating the Bishop parameter χ or the Fredlund parameter φb......Page 85
2.5.2 Evaluating χ from the results of various types of sheartest, assuming that the equivalent test result for the saturated soil represents true effective stresses......Page 88
2.5.3.1 Isotropic compression......Page 93
2.5.3.2 Isotropic swell......Page 94
2.5.4 Summary of χ values from isotropic compression, swell and swelling pressure......Page 95
2.5.5 The effect of stress path on values of χ......Page 97
2.5.6 The χ parameter for compression of a collapsing sand......Page 98
2.6.1 Shear strength......Page 101
2.6.3 Summary......Page 105
2.7 Empirical methods of estimating parameter χ......Page 108
2.8 The limits of effective stress in dry soils (Blight, 2011)......Page 109
2.8.1 The experiment......Page 110
References......Page 112
Appendix A2: Equation for the solution of a bubble in a compressible container......Page 114
Plate......Page 115
3.1 Direct or primary measurement of suction......Page 116
3.1.2 De-airing and testing fine-pored ceramic filters for air entry......Page 119
3.1.3 The effects of capillarity on the de-airing process......Page 121
3.1.5 Direct measurement of suctions exceeding 100 kPa......Page 122
3.1.6 Null-flow methods of measuring suction......Page 126
3.2 Indirect or secondary methods of measuring water content or suction......Page 129
3.2.1 Filter paper......Page 130
3.2.2 Thermal conductivity sensor......Page 134
3.2.3 Electrical conductivity sensor......Page 135
3.2.4 Time domain reflectometry (TDR)......Page 137
3.2.5 Dielectric sensors......Page 140
3.3.1 Control of relative humidity......Page 143
3.3.2 Measuring relative humidity......Page 146
3.3.2.1 Thermocouple psychrometer......Page 147
3.3.2.2 Transistor psychrometer......Page 149
3.3.2.3 Chilled-mirror psychrometer......Page 150
3.4 A commentary on the use of the Kelvin equation as a measure of total suction......Page 153
3.5.2 Near-surface changes of water content as a result of evapotranspiration (Blight, 2008)......Page 156
3.5.3 A comparison of field measurements of suction by means of thermocouple psychrometers, gypsum blocks and glass fibre mats (Harrison & Blight, 2000)......Page 158
3.5.4 Use of tensiometers to monitor the rate of infiltration of surface flooding into unsaturated soil strata (Indrawan, et al., 2006)......Page 160
3.5.5 Use of suction gradients measured by gypsum blocks to examine the patterns of water flow in a stiff fissured clay (Blight, 2003)......Page 163
3.5.6 Use of high tension tensiometers to monitor suctions in a test embankment (Mendes, et al., 2008)......Page 165
3.5.7 Effect of covering the surface of a slope cut in residual granite soil with a capillary moisture barrier to stabilize the slope against surface sloughing (Rahardjo, et al., 2011)......Page 167
3.6.1 Controlling alkali–aggregate reaction (AAR) in concrete......Page 169
References......Page 173
Plates......Page 175
4. Interactions between the
atmosphere and the Earth’s
surface: Conservative
interactions – infiltration,
evaporation and water storage......Page 180
4.1 The atmospheric water balance......Page 181
4.2 The soil water balance......Page 183
4.3 Measuring infiltration (I) and runoff (RO)......Page 184
4.4 Estimating evapotranspiration by solar energy balance......Page 190
4.5.1 Field experiments using a large cylindrical pan set into the ground surface (Blight, 2009a)......Page 193
4.5.2 Field measurement of the water balance for a landfill......Page 195
4.5.3 Evaporation from experimental landfill capping layers......Page 196
4.5.4 Evaporation from a grassed, fissured clay surface (Clarens, South Africa)......Page 197
4.5.5 Near-surface movement of water during evapotranspiration......Page 203
4.5.6 Drying of tailings beaches deposited on tailings storage facilities......Page 204
4.6.1 Water or soil heat as sources and drivers of evaporation......Page 208
4.6.2 The role of wind energy......Page 211
4.7 Evaporation from unsaturated sand and the effect of vegetation – the efficiency factor η......Page 213
4.8 Fundamental mechanisms of evaporation – discussion......Page 215
4.9 Estimating evapotranspiration by means of lysimeter experiments......Page 216
4.10 Depth of soil zone interacting with the atmosphere (also see section 4.5.5)......Page 219
4.11 Recharge of water table and leachate flow from waste deposits......Page 226
4.12 Estimating and measuring water storage capacity (S) for active zone......Page 227
4.13 Seasonal and longer term variations in soil water balance......Page 233
4.14.1 Effects on soil strength of a falling water table (also see section 8.8.1)......Page 235
4.14.2 Effects of a rising water table – surface heave (also see section 8.6.2)......Page 237
4.15.1 Stresses in a shrinking soil......Page 241
4.15.2 Cracking in a shrinking soil......Page 243
4.15.3 Formation of shrinkage cracks at the surface......Page 244
4.15.4 Formation of shrinkage cracks at depth......Page 245
4.15.7 Fissures in profiles that seasonally shrink and swell......Page 246
4.15.8 Spacing of cracks on the surface......Page 247
4.16 Damage to road pavements by upward migration of soluble salts......Page 249
4.17.1 Installation of root barriers......Page 251
4.17.3 Examination of the exhumed root barriers......Page 253
4.18 Use of an unsaturated soil layer to insulate flat (usually concrete) roofs (Gwiza, 2012)......Page 255
4.19.1.1 The influence of climate on landfilling practice......Page 257
4.19.1.3 Water content of incoming waste......Page 258
4.19.1.5 Evaporation from a landfill surface......Page 259
4.19.1.6 Infiltrate-stabilize-evapotranspire (ISE) landfill covers......Page 260
4.19.1.7 Field tests of ISE caps under summer and winter
rainfall conditions......Page 261
4.19.1.8 Rainfall infiltration and water storage......Page 262
4.19.1.9 Concluding discussion......Page 264
4.19.2.1 Introduction......Page 267
4.19.2.2 Some effects of raising the height of a landfill......Page 269
4.19.2.3 The measuring cells and their prior use......Page 270
4.19.2.4 The experimental raising and its effect on settlement
and leachate flow......Page 272
4.19.2.5 Relationship between leachate quality and leachate
flow rate......Page 275
4.19.2.6 Compression characteristics of waste......Page 276
4.19.2.7 Summary and conclusions......Page 277
4.19.3.1 Introduction......Page 278
4.19.3.2 Corrosion cause and progress......Page 279
References......Page 283
A4.1 Calculating G, WH, H......Page 288
A4.2 Calculating kT......Page 289
A4.3 Conversion of volumetric water content wv
to gravimetric water content wg......Page 290
Plates......Page 291
5.1 Factors controlling erosion from slopes......Page 298
5.1.1 Results of early erosion measurements......Page 299
5.1.2 Wind erosion compared with water erosion......Page 301
5.1.3 Acceptable erosion rates for slopes......Page 302
5.2 The mechanics of wind erosion......Page 304
5.2.1 Variation of wind speed with height above ground level......Page 305
5.2.2 Erosion and transportation by wind......Page 306
5.3 Wind speed profiles over sand dunes and tailings storages......Page 307
5.4 Wind tunnel tests on model waste storages......Page 308
5.5 Wind flow over top surface of storage......Page 310
5.7 Protection of slopes against erosion by geotechnical means......Page 312
5.7.2 Rock cladding......Page 314
5.8 Full-scale field trials of rock cladding and rock armouring......Page 315
5.9 Comments on wind and water erosion......Page 316
5.10 Dispersive soils and piping erosion......Page 317
5.11 Examples of piping erosion occurring in acid mine tailings......Page 319
5.12 Other examples of failures by piping erosion......Page 321
5.12.1 Failure of Teton dam (USA) (Seed & Duncan, 1981)......Page 322
5.12.2 Gennaiyama and Goi dams (Japan) − failure by piping along outlet conduits (N'Gambi, et al., 1999)......Page 326
5.12.3 Cut-off trench, Lesapi dam, Zimbabwe − stresses indicate piping unlikely (Blight, 1973)......Page 330
5.12.4 Concrete spillway, Acton Valley dam, South Africa, piping along soil to concrete interfaces......Page 331
5.12.5 Termite channels and piping flow......Page 335
References......Page 336
Plates......Page 338
6.1 The compaction process......Page 346
6.3 Mechanisms of compaction......Page 351
6.4 Laboratory compaction......Page 353
6.5.2 Soil aggregations or clods not broken down......Page 354
6.5.3 Other treatments that affect laboratory compaction curve......Page 356
6.6 Roller compaction in the field......Page 357
6.7 Relationships between saturated permeability to water flow and optimum water content......Page 359
6.8 Designing a compacted clay layer for permeability......Page 361
6.9 Seepage through field-compacted layers......Page 363
6.10 Control of compaction in the field......Page 364
6.10.2 In situ water content......Page 366
6.10.5 In situ permeability......Page 367
6.10.7 Recipe specifications......Page 369
6.11 Special considerations for work in climates with large rates of evaporation......Page 370
6.12.2 Compactor performance......Page 373
6.13 Compaction of residual soils......Page 374
6.14 Mechanics of unsaturated compacted soils during and after construction......Page 377
6.15 Pore air pressures caused by undrained compression of compacted soil......Page 379
6.16 Use of compaction to improve foundation conditions......Page 385
6.17 Settlement of an earth embankment constructed of compacted residual soil (Blight, et al., 1980)......Page 389
6.18 Summary......Page 393
References......Page 394
Appendix A6: Development of Hilf's equation in mass terms......Page 395
Plate......Page 396
7.1 Darcy's and Fick's laws of steady-state seepage flow......Page 398
7.2 Displacement of water from soil by air......Page 401
7.3 Unsteady flow of air through partly saturated and dry soils......Page 403
7.5 Unsteady flow of air through unsaturated soil......Page 405
7.6 Measuring permeability to water flow in the laboratory......Page 407
7.7 Observed differences between small scale and large scale permeability measurements......Page 408
7.8 Laboratory tests for permeability to water flow......Page 410
7.9 Measuring permeability to air flow......Page 413
7.10 Water permeability of unsaturated soils......Page 416
7.11.1 Permeability from surface ponding or infiltration tests......Page 419
7.11.2.1 Variable head tests......Page 423
7.11.2.4 Determination of the effective head at test zone, Hc......Page 426
7.12.1 Tests for rough estimates of permeability......Page 429
7.12.3 Extension of Matsuo, et al.'s method......Page 430
7.12.3.1 Seepage pits......Page 431
7.12.3.2 Calibration of measured water levels......Page 432
7.12.3.5 Analysis of permeability and results......Page 433
7.14 Permeability characteristics of residual soils......Page 439
7.15.1 Introduction......Page 441
7.15.2 Calculation of variation of ua with time after start of loading......Page 442
7.15.3 Use of theory in silo design......Page 443
7.16.1 Field sites and installations......Page 447
7.16.2 Pressure profiles for steady-state injection of air into single wells......Page 448
7.16.3 Pressure profiles for unsteady injection of air into a single well......Page 450
7.16.4 Additive effect of adjacent injection wells......Page 451
7.16.5 Pressure contours for steady-state air injection into a single well......Page 452
7.17 Solubilization achieved by aeration......Page 453
References......Page 456
A7.1 Hvorslev's method......Page 457
A7.3 Application of calculation method......Page 458
Plates......Page 459
8.1 Compressibility and volume change of unsaturated soils......Page 462
8.2 The process of compression and swell in unsaturated soils......Page 463
8.3 Measuring the compressibility of unsaturated soils (Barksdale & Blight, 1997)......Page 465
8.3.1 The conventional plate load test......Page 466
8.3.1.1 Test pit......Page 467
8.3.1.4 Load application......Page 468
8.3.1.6 Primary consolidation settlement......Page 469
8.3.2 The cross-hole plate test......Page 471
8.3.3.1 Screw plate geometry......Page 472
8.3.3.4 Load-deflection test......Page 473
8.3.3.5 Elastic modulus......Page 474
8.3.4 The Menard pressuremeter test......Page 475
8.3.4.1 Hole preparation......Page 476
8.3.4.2 Equipment calibration......Page 477
8.3.5 Slow cycled triaxial tests......Page 480
8.3.5.1 Details of test......Page 481
8.3.5.2 Modulus of elasticity......Page 483
8.3.6 Comparisons of different methods of assessing elastic modulus for unsaturated soils......Page 484
8.4 Settlement predictions for raft and spread foundations......Page 485
8.4.2 Strain influence diagram method......Page 486
8.4.2.2 Adjacent footings......Page 489
8.4.2.4 Rectangular foundations: Generalized strain influence
diagrams......Page 490
8.4.2.6 Circular rigid foundation, increasing stiffness with depth......Page 491
8.4.3 Menard method for calculating settlement of shallow foundations......Page 493
8.5.1 Sellgren's method for predicting settlement of piles......Page 494
8.6 Movement of shallow foundations on unsaturated soils......Page 496
8.6.1 Heave of expansive soils......Page 497
8.6.2 Prediction of heave in expansive soils......Page 502
8.7.1 Ancient wind-blown sands......Page 507
8.7.3 Combating effects of collapse settlement......Page 511
8.8.1 Settlement of two tower blocks on unsaturated residual andesite lava (also see sections 4.14.1 & 4.14.2)......Page 512
8.8.2 Settlement of an apartment block built on loess in Belgrade (Popescu, 1998)......Page 516
8.8.3 Settlement of coal strip-mine backfill......Page 517
8.8.4 Settlement of mine backfill under load of hydraulically placed ash......Page 520
8.8.5 Summary of mine backfill and other settlement measurements......Page 521
8.9.1 Similarities between heave and settlement analyses......Page 524
8.9.2 The profile of excess pore pressure for heave......Page 526
8.9.3 Measurement of the coefficient of swell, cs, for diffusional flow......Page 527
8.9.4 Drainage conditions for the heave process......Page 528
8.9.4.2 Vertical rainfall penetration followed by lateral
diffusional flow......Page 530
8.9.5 Relationship between heave and changes in suction......Page 531
8.9.6 Accuracy of time-heave prediction......Page 532
8.10 Preheaving of expansive clay soils by flooding......Page 534
8.11 Biotic activity (also see section 5.12.5)......Page 542
References......Page 544
Plates......Page 547
9.1 Do matrix and solute suctions both contribute to the strength of unsaturated soil?......Page 550
9.2 Ranges of strength of interest for practical unsaturated soil mechanics......Page 555
9.2.1 Shear strength of a beach surface......Page 556
9.2.2 Strength imparted by suction across the failure surface of a landslide......Page 557
9.2.3 Water content and shear strength of air-drained fill......Page 558
9.2.4 Effect of hydrostatic suction on in situ strength of soil......Page 560
9.2.5 Strength of extremely desiccated clays......Page 561
9.3 Practical measurement of shear strength of unsaturated soils......Page 562
9.3.1 Effects of sample size on measured strength......Page 564
9.4 Laboratory shear strength tests......Page 567
9.4.1.1 Box size and shape and specimen thickness......Page 571
9.4.1.2 Status of consolidation, drainage and saturation
conditions......Page 572
9.4.1.4 Rate of shearing......Page 573
9.4.1.7 Maximum shear displacement......Page 574
9.4.1.8 Direct shear tests for initially unsaturated soils......Page 575
9.4.2 Triaxial testing......Page 577
9.4.2.1 Triaxial test variables......Page 580
9.4.2.4 Consolidation stress system......Page 581
9.4.2.5 Loading (deviator) stress system......Page 582
9.4.2.6 Saturation conditions and back pressure application
(for CU and CD tests)......Page 583
9.4.2.7 Controlled strain or controlled stress testing......Page 584
9.4.2.9 Cell and consolidation pressures to be applied......Page 585
9.4.2.10 Rate of strain......Page 586
9.4.2.11 Triaxial testing of stiff fissured clays......Page 588
9.4.3 Determination of K0 from triaxial test......Page 591
9.5 In situ strength testing......Page 593
9.5.1 Field direct shear test......Page 594
9.5.1.1 Examples of in situ direct shear tests......Page 595
9.5.2.1 Principle of vane test......Page 600
9.5.2.3 Mode of failure......Page 601
9.5.2.4 Shearing under undrained conditions......Page 602
9.5.2.5 Vane size and shape......Page 603
9.5.2.7 Comparison of vane shear strength of unsaturated soilswith other types of measurement......Page 605
9.5.4 Standard penetration test (SPT)......Page 606
9.5.4.2 Split spoon sample tube......Page 608
9.5.5 Cone penetration test (CPT)......Page 610
9.5.5.1 Field penetrometer testing of unsaturated soils......Page 611
9.5.6 Interpretation of cone resistance in cohesionless sands and silts......Page 614
9.6 Performance of tension piles subjected to uplift by expansive clays......Page 619
9.6.1 Shear strength......Page 620
9.6.2 Field test on instrumented pile group......Page 621
9.6.3 Effect of loading on pile previously subjected to uplift......Page 624
9.6.4 Conclusions......Page 625
9.7 More detailed examination of Amsterdamhoek landslides......Page 626
9.8 Sloughing of dune slopes caused by overnight dew......Page 628
References......Page 629
Plates......Page 632
Subject index......Page 636