Barnes - Chapter 1

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Contents

Made ground 17 Organic soils 17 Volcanic soil 19 Particle size fractions – fundamental basis 19 Very coarse soil 20 Coarse soil 20 Fines 21 Composite soils 21 Fine soil 21 Mass structure 23 Degree of weathering 24 Geological origin 24 Soil classification 26 Particle density 26 Particle shape 26 Particle size distribution 27 Grading characteristics 29 Density 30 Density index 31 Water content 32 Atterberg limits 34 Activity index 38 Volumetric shrinkage 38 Shrinkage limit 39 Soil model 40 Pore size distribution 42 Summary 43 Further Reading 44 Worked Examples 45 Exercises 52

Preface xiii Aims of the book xiii The Eurocode Approach xiii Changes in the Fourth Edition xiv Companion website xiv Acknowledgements xiv Acknowledgements xv Case studies xvii Videos xviii List of symbols xix Note on units xxiv SI units xxiv Mass, force and weight xxiv Stress and pressure xxiv Density and unit weight xxiv 1 Soil formation and nature Objectives Soil formation Man-made soils Contaminated and polluted soils Naturally occurring soils In situ soils – weathered rocks In situ soils – peat Water-borne soils Glacial deposits Wind-blown soils Soil particles Nature of particles Clay minerals Soil structure Cohesive soils Granular soils Summary Further Reading

1 1 1 1 2 2 2 3 3 4 6 6 6 7 10 10 14 15 15

2 Soil description and classification Objectives Soil description Soil categories

16 16 16 17

3

Permeability and seepage 53 Objectives 53 Permeability 53 Introduction 53 Groundwater 53 Flow problems 54 Flow into excavations 54 Flow around cofferdams 54 v

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vi Contents Dewatering 55 Flow through earth structures 55 Stability problems ‘running sand’ 55 Boiling or heaving in cofferdams 55 Piping 56 Heaving beneath a clay layer 56 Uplift pressures 56 Soil pores 57 Pressure and head 57 Darcy’s Law 58 Effect of temperature 58 Empirical correlations for k 59 Layered soils 60 Laboratory test – constant head permeameter 61 Laboratory test – falling head permeameter 62 Laboratory test – hydraulic cell – vertical permeability 63 Laboratory test – hydraulic cell – horizontal permeability 64 Laboratory test – triaxial cell – vertical permeability 65 Borehole tests – open borehole 65 Borehole tests – packer tests 67 Borehole tests – piezometers 68 Pumping tests 69 Groundwater lowering and pore pressure control methods 70 Seepage 72 Seepage theory 72 Flow nets 74 Flow net construction 75 Seepage quantities 77 Seepage quantities – plan flow net 78 Total head, elevation head and pressure head 79 Pore pressure and uplift pressure 80 Failure by uplift (buoyancy) 80 Seepage force 80 Quick condition, boiling and internal erosion 81 Critical hydraulic gradient 81 Failure by internal erosion 81 Failure by heave – sheet piling 82 Failure by piping 82 Seepage through earth dams 83 Seepage through flood banks, levees 83 Soil filters 84

Summary Further Reading Case Studies Worked Examples Exercises

86 86 87 92 102

4 Effective stress and pore pressure 105 Objectives 105 Total stress 105 Total and effective stress above the water table 105 Pore pressure below the water table 106 Total stress below the water table 107 Effective stress 107 Effective stress below the water table 108 Stress history 109 Normally consolidated clay 109 Overconsolidated clay 110 Overconsolidation ratio 111 Overconsolidation ratio in the ground 111 Desiccated crust 111 Present state of stress in the ground 113 Mohr’s circle of stress 113 In situ horizontal and vertical stresses 114 Undrained and drained conditions 116 Loading 117 Unloading 118 Pore pressure parameters – theory 118 Pore pressure parameters A and B 120 Capillary rise above the water table 121 Capillary break layers 122 Effective stresses above the water table 123 Suctions 124 Climatic and desiccation effects in the aeration zone 125 Expansive soils 127 Frost action in soils 128 Depth of frost penetration 128 Frost susceptibility 130 Frost heave test 131 Ground freezing technique 131 Summary 131 Further Reading 132 Case Studies 133 Worked Examples 136 Exercises 140

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Contents vii 5 Contact pressure and stress distribution 142 Objectives 142 Contact pressure 142 Contact pressure – uniform loading 142 Contact pressure – point loading 143 Stress distribution 144 Stresses beneath point load and line load 144 Assumptions 144 Foundation depth 146 Stresses beneath uniformly loaded areas 146 Bulbs of pressure 147 Stresses beneath a flexible rectangle and circle 147 Principle of superposition 147 Stresses beneath flexible area of any shape 147 Stresses beneath a flexible rectangle – finite soil thickness 147 Stresses beneath a flexible circle – finite soil thickness 151 Stresses beneath a rigid rectangle 151 Embankment loading 151 Summary 154 Further Reading 154 Worked Examples 155 Exercises 159 6 Compressibility and consolidation 161 Objectives 161 Introduction 161 Compressibility 161 Void ratio/effective stress plot 161 Reloading curves 163 Preconsolidation pressure sp', consolidation yield stress sy' 163 Overconsolidation ratio (OCR) 163 Effect of sampling disturbance 163 Determination of sp' 164 In situ curve for normally consolidated clay 165 In situ curve for overconsolidated clay 165 Effect of load increments 166 Effect of duration of load 166 Effect on pore size distribution 166

Effect of ageing 167 Compression of residual soils 168 Isotropic compression 169 Anisotropic compression 169 Consolidation 170 Introduction 170 Terzaghi theory of one-dimensional consolidation 170 Solution of the consolidation equation 171 Isochrones 172 Average degree of consolidation 173 Oedometer test 175 Rowe consolidation cell 176 Consolidation properties 177 Coefficient of consolidation, cv – root time method 178 Coefficient of consolidation, cv – log time method 180 In situ cv values 181 Two- and three-dimensional consolidation 181 Correction for construction period 182 Underconsolidation – recent sediments and backfills 183 Precompression by surcharging 185 Vacuum precompression 187 Radial consolidation for vertical drains 188 Summary 191 Further Reading 191 Case Studies 192 Worked Examples 197 Exercises 205 7 Shear strength 208 Objectives 208 Introduction 208 Stresses and strains in soils 209 Representation of stresses 209 Pole 209 Principal stresses 210 Axial symmetry 210 Plane strain 211 K0 condition 211 Normal and shear strains 211 Mohr circle of strain 212 Volumetric strains 212

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viii Contents

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Shear strength 214 Effect of strain 214 Idealised stress–strain relationships 215 Idealised yield and plasticity 216 Yield curves 216 Failure criterion 217 Failure of soil in the ground 217 Stress paths 219 Effects of drainage 220 Test procedures 223 Shear strength of sand 224 Stress–strain behaviour 224 Shear box test 225 Effect of packing and particle nature 226 Constant volume condition 228 Effect of density 228 Effect of confining stress and crushing 229 Shear strength of clay 229 Effect of sampling 229 Undrained strength, cu 230 Strength index tests 230 Strength tests 231 Unconfined compression test 231 Field vane test 231 Triaxial test 233 Triaxial unconsolidated undrained (UU) test 234 Multi-stage (UU) test 236 Effect of clay content and mineralogy 236 Partially saturated clays 236 Fissured clays 237 Variation with depth 238 Frictional characteristics 239 Test procedures 239 Triaxial consolidated undrained (CU) test 240 Triaxial consolidated drained (CD) test 242 Critical state theory 243 Parameters 243 State boundary surface 243 Isotropic normal consolidation line (ICL) 244 K0 normal consolidation line (K0 CL) 245 Critical state line (CSL) 245 Roscoe surface 246 Tension cut-off 247 Hvorslev surface 248

The elastic wall Real soils Residual strength Summary Further Reading Case Study Worked Examples Exercises

249 249 249 250 251 251 253 257

8 Shallow foundations – stability 260 Objectives 260 Shallow foundations 260 Definition 260 Geotechnical risk 260 Spread foundations 261 Types of foundation 261 Strip foundations 261 Pad foundations 262 Raft foundations 263 Depth of foundations 263 Adequate bearing stratum 264 Seasonal moisture variations 264 Effects of tree roots 265 Frost action 266 River erosion 267 Water table 268 Super-elevation 268 Design requirements 268 Traditional approach compared with the Eurocodes 269 Design approach 270 Bearing resistance 270 Modes of failure 270 Bearing capacity and bearing resistance 270 Shape factors 273 Depth factors 273 Base inclination factors 274 Bearing resistance – overturning 274 Eccentric loading 274 Inclined loading 275 Summary 275 Different soil strength cases 275 Effect of water table 276 Net ultimate bearing capacity 276 Effect of compressibility of soil 277 Sliding 277

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Bearing capacity – two layers a) two clay layers 278 b) sand overlying clay 279 Allowable bearing pressure of sand 280 Introduction 280 Settlement limit 280 Allowable bearing pressure 280 Corrected SPT N values 281 Summary 283 Further Reading 283 Case Studies 284 Worked Examples 287 Exercises 292 9 Shallow foundations – settlements 295 Objectives 295 Introduction 295 Are settlement calculations required?

296 Elastic methods – assumptions 296 Elastic displacement method 296 Immediate settlement 298 Introduction 298 General method 298 Principle of superposition 299 Principle of layering 299 Rigidity correction 299 Depth correction 302 Effect of local yielding 303 Estimation of undrained modulus Eu 303 Consolidation settlement 304 General 304 Compression index Cc method 305 Oedometer modulus Eoed or mv method 306 Total settlement 307 Skempton–Bjerrum method 307 Elastic drained method 308 Estimation of drained modulus E' 310 Proportion of immediate to total settlement 310 Secondary compression 311 Introduction 311 General method 312 Estimation of Ca or ea values 312 Sands 312 Methods of estimating settlements 313 Schmertmann’s method 314 Burland and Burbridge’s method 315

Contents ix

Permissible settlements 317 Definitions of ground and foundation movement 317 Criteria for movements 318 Routine settlement limits 318 Summary 320 Further Reading 320 Case Studies 321 Worked Examples 326 Exercises 333 10 Pile foundations 335 Objectives 335 Pile foundations 335 Introduction 335 Types of pile 336 Loading conditions 336 Uncertainty of design calculation methods 337 Limit states 337 Pile load tests 337 Compressive resistance from static load tests 338 Compressive resistance from ground test results 339 Compressive resistance from other methods 340 Design values of compressive resistance 341 Weight of pile 341 Bored piles in clay 341 Geometric data 341 End-bearing resistance qb 341 Adhesion ca 342 Driven piles in clay 343 End-bearing resistance qb 343 Adhesion ca – installation effects, soft clay 343 Adhesion ca – installation effects, stiff clay 344 Adhesion ca – values 344 Effective stress approach for adhesion 345 Driven piles in sand 346 Effects of installation 346 End bearing resistance qb 346 Critical depth 346 Skin friction fs 348 Bored piles in sand 350

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x Contents Mobilisation of base and shaft loads 350 Downdrag (negative skin friction) 350 Causes of downdrag 350 Determination of downdrag 351 Pile groups 352 Stiffness of pile cap and structure 352 Pile spacing 352 Stressed zone 352 Load variation 353 Efficiency 353 Ultimate capacity 354 Settlement ratio 355 Settlement of pile groups 357 Summary 358 Further Reading 358 Case Studies 358 Worked Examples 361 Exercises 367 11 Lateral earth pressures and retaining structures 369 Objectives 369 Lateral earth pressures 369 Introduction 369 Effect of horizontal movement 370 Effect of wall flexibility and propping 373 Effect of wall friction 373 Coulomb theory – active force 374 Coulomb theory – passive force 375 Limitations of the Coulomb theory 376 Earth pressure coefficients 376 Effect of cohesion intercept c' 378 Minimum equivalent fluid pressure 379 Effect of water table – gravity walls 380 Effect of water table – embedded walls 380 Undrained conditions 381 Earth pressures – undrained condition 382 Tension cracks 382 Uniform surcharge 383 Line loads and point loads 384 Earth pressures due to compaction 384 Retaining structures 385 Introduction 385 Basement walls 387 Bridge abutments 387 Gabions and cribwork 388 Design of gravity walls 389 Serviceability limit states 389

Ultimate limit states 389 Loss of overall stability 389 Overturning or rotational failure 390 Bearing pressure under the toe 390 Bearing capacity 391 Sliding 391 Failure of structural elements 391 Design of embedded walls 391 Cantilever embedded walls – general 392 Cantilever embedded walls – design 392 Single anchor or propped embedded walls – general 393 Single anchor or propped embedded walls – design 393 Design methods 394 Gross pressure method 394 Net available passive resistance method 394 Factor on strength method 395 BS 8002 method 395 Anchorages for embedded walls 395 Strutted excavations and cofferdams 396 Introduction 396 Strut loads 397 Base stability of excavations 398 Reinforced soil 398 Reinforced soil walls – construction 399 Effects of reinforcement 399 Reinforced soil walls – design 400 External stability 400 Internal stability – general 402 Tensile rupture 402 Pull-out resistance or adherence 403 Internal stability – tie-back wedge method 403 Coherent gravity method 405 Summary 406 Further Reading 407 Case Studies 407 Worked Examples 411 Exercises 424 12 Slope stability 426 Objectives 426 Natural and artificial slopes 426 Introduction 426 Types of mass movement 426 Natural slopes 426

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Artificial slopes or earthworks 429 Short-term and long-term conditions 430 Methods of analysis 433 Plane translational slide – general 433 Plane translational slide – limit state approach 434 Plane translational slide – special cases 435 Stability of vertical cuts 437 Circular arc analysis – general 438 Circular arc analysis – undrained condition or fu 5 0° analysis 438 Undrained analysis – the overdesign factor 439 Tension crack 439 Undrained analysis stability charts – Taylor’s method 439 Effective stress analysis 441 Effective stress analysis – method of slices 441 Bishop simplified method 443 Bishop method – overdesign factor on strength 443 Bishop method – overdesign factor on moments 444 Favourable and unfavourable actions 445 Pore pressure ratio ru 445 Stability coefficients – ru method 446 Stability charts – ultimate limit state 446 Submerged slopes 449 Rapid drawdown 449 Non-circular slip surfaces 450 Wedge method – single plane 451 Wedge method – multi-plane 451 Factors affecting stability and slope design 452 Summary 453 Further Reading 454 Case Studies 454 Worked Examples 458 Exercises 468 13 Earthworks and soil compaction 471 Objectives 471 Earth structures 471 Introduction 471 Typical examples 471

Contents xi

Construction expedients – improve the earth structure 471 Construction expedients – improve the underlying ground 473 Earthmoving and fill materials 474 Earthmoving plant 474 Purpose and types of materials 475 Suitability of fill material 477 Suitability of granular soils 478 Suitability of cohesive soils 478 Moisture condition test 479 Efficiency of earthmoving 481 Material problems 482 Softening 482 Bulking 483 Soil compaction 485 Factors affecting compaction 485 Field compaction 486 Compaction plant 487 Specification of compaction 488 Control of compaction in the field 490 Laboratory compaction 492 Light compaction test 492 Heavy compaction 493 Vibrating hammer 494 Air voids lines 494 Correction for oversize particles 494 California Bearing Ratio (CBR) test 495 Addition of lime 496 Lime stabilisation 496 Cement stabilisation 497 Summary 497 Further Reading 498 Case Study 499 Worked Examples 501 Exercises 507 14 Site investigation 509 Objectives 509 Site investigation 510 Introduction 510 Relationship with geotechnical design 510 Stages of investigation 511 Desk study 511 Site inspection 512 Preliminary studies report 512 Ground investigation 512 Extent of the ground investigation 512

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xii Contents Depth of exploration 513 Choice of method of investigation 513 Methods of ground investigation 514 Undisturbed sampling – sampling quality 518 Types of samples 518 Methods of in situ testing 522 Groundwater observations 527 Investigation of contaminated land 530

Ground investigation report Presentation of geotechnical information Factual report Geotechnical evaluation Summary Further Reading

531 531 531 532 536 536

Glossary 537 References 539 Index 551

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1

Soil formation and nature

OBJECTIVES ■■

To recognise the wide variety of soil types that exist in nature and the importance of geological processes in their individual depositional and post-depositional environments.

■■

To appreciate that ‘soils’ comprise particles. These particles may be of a granular nature, from silt to boulder sizes, or may impart a cohesive nature when clay minerals are present. Some soils may also contain or comprise entirely organic matter.

■■

To understand how the nature of the soil particles, their combinations and their structural arrangements determine the engineering behaviour of the soil.

This chapter has been divided into three sections: soil formation, soil particles and soil structure.

Soil formation Soils in the engineering sense are either naturally occurring or man-made. They are distinguished from rocks because the individual particles are not sufficiently bonded together.

Man-made soils These are described as made ground or fill (BRE Digest 427:1998). The main types of made ground are: ■■ ■■

Waste materials; Selected materials.

demolition rubble, from industrial processes such as ashes, slag, pulverised fuel ash (PFA), mining spoil, quarry waste, industrial by-products and from domestic waste in landfill sites.

They can be detrimental to new works through being soluble, chemically reactive, contaminated, hazardous, toxic, polluting, combustible, gas generating, swelling, compressible, collapsible or degradable.

All waste materials should be treated as suspect because of the likelihood of extreme variability and compressibility (BRE Digest 427: Part 1). These deposits have usually been randomly dumped and any structures placed on them will suffer differential settlements. There is also increasing concern about the health and environmental hazards posed by these materials.

Selected materials

Waste materials These include the surplus and residues from construction processes such as excavation spoil and

These are materials that have none or very few of the detrimental properties mentioned above. They are spread in thin layers, are well compacted and may be referred to as engineered fill (BRE Digest 427: Part 3). This gives a high shear strength and

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2 Soil Mechanics: Principles and Practice low compressibility, to provide adequate stability and ensure that subsequent volume changes and settlements are small. They are used to form a range of earth structures such as highway embankments and earth dams, flood walls, backfilling around foundations, behind retaining walls and in reinforced soil.

Contaminated and polluted soils Due to past industrial activities many sites comprising naturally occurring soils have been contaminated (there are potential hazards) or polluted (there are recognisable hazards) by the careless or intentional introduction of chemical substances.

These contaminants could comprise metals (arsenic, cadmium, chromium, copper, lead, mercury, nickel, zinc), organics (oils, tars, phenols, polychlorinated biphenyl (PCB), cyanide) or dusts, gases, acids, alkalis, sulphates, chlorides and many more compounds.

Several of these may cause harm to the health of animals, plants or people working in or occupying the site and some may cause degradation of building materials buried in the ground such as concrete, metals, plastics or timber.

Naturally occurring soils The two groups of naturally occurring soils are those formed in situ and those transported to their present location. There are two very different types of soils formed in situ: weathered rocks and peat. Transported soils are moved by the principal agents of water, wind and ice although they can also be formed by volcanic activity and gravity.

In situ soils – weathered rocks Weathering produces the decomposition and disintegration of rocks. Disintegration is produced largely by mechanical weathering, which is most intense in cold climates and results in fragmentation or fracture of the rock and its mineral grains. Chemical alteration results in decomposition of the hard rock minerals to softer clay minerals and is most intense in a hot, wet climate such as in the tropics.

Weathering gradually converts rock to a soil. BS EN ISO 14689-1:2003 requires that the weathering profile is described in terms of three units: rock ➤ rock and soil ➤ soil. The scale of weathering of rock masses from this BS is given in Table 1.1.

Table 1.1 Mass weathering grades (From BS EN ISO 14689-1:2003)

Unit

Grade

Term

Description All rock material is converted to soil. The mass structure and material fabric are destroyed. There is a large change in volume, but the soil has not been significantly transported.

5

Residual soil

4

Completely weathered

3

Highly weathered

2

Moderately weathered

1

Slightly weathered

Discolouration indicates weathering of rock material and discontinuity surfaces.

0

Fresh

No visible sign of rock material weathering; perhaps slight discolouration on major discontinuity surfaces.

SOIL

ROCK AND SOIL

ROCK

All rock material is decomposed and/or disintegrated to soil.

The original mass structure is still largely intact.

More than half of the rock material is decomposed or disintegrated.

Fresh or discoloured rock is present either as a discontinuous framework or as corestones.

Less than half of the rock material is decomposed or disintegrated.

Fresh or discoloured rock is present either as a continuous framework or as corestones.

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Chapter 1 Soil formation and nature 3 Table 1.2 Soil/rock interface

Unit

SOIL ROCK AND SOIL

Grade1

Tropical soils2

5

Solum

4

e.g. excavatability, slope stability

3 Weathered bedrock

1 ROCK

Bedrock

0 soil/rock interface nterface

Stricter engineering applications e.g. settlements, bearing capacity, swelling/shrinkage, erosion

Saprolite

2

General engineering applications

From BS EN ISO 14689-1:200 14689-1:2003

1

BS EN 14689-2 states that the weathered products, which could be sand from a sandstone or clay from a mudstone, can be described as a matrix and the less weathered remnants of rock described as lithorelics or corestones. At the mass scale the distribution and proportion of the corestones vs. matrix should be recorded. With more intense weathering the matrix (a soil) would provide a continuous framework and the principles of soil mechanics could apply, notably strength, stiffness and permeability.

The soil/rock interface will depend on the extent of this framework, or the proportion and extent of the matrix, and on the engineering application, as shown in Table 1.2.

In situ soils – peat Peats are almost entirely organic matter, comprising partly decomposed and fragmented plant remains.

They constitute 5 to 8% of the land surface of the earth (Mesri and Ajlouni, 2007). They are referred to as cumulose soils and may occur as high or moor peats comprising mostly mosses, raised bogs consisting of sphagnum peat and low or fen peat composed of reed and sedge peat. Moor and bog peats tend to be brown or dark brown in colour, fibrous and lightly decomposed while fen peats are darker, less fibrous and more highly decomposed.

After Anon (1990)

2

Landva and Pheeney (1980) suggested a suitable classification for peats based on genera, degree of humification, water content and the content of fine fibres, coarse fibres and wood and shrub remnants.

This is summarised in Table 2.1 in Chapter 2.

Water-borne soils (Figure 1.1) For soils to be deposited they have to be first removed from their original locations or eroded and then transported. During these processes the particles are also broken down or abraded into smaller particles.

The most erosive locations are in the highland or mountainous regions and upper reaches of rivers, especially during flood conditions and along the coastline, particularly at high tides and during storms. Cliff erosion can produce a wide variety of particles sorted into beach materials (sands, gravels) and finer materials which are carried out to sea.

Soils deposited by water tend to be named according to the deposition environment as shown in Figure 1.1, for example, marine clays. Whether a particle can be lifted into suspension depends on the size of the particle and the water velocity so that further downstream in rivers where the velocity decreases certain particles tend to be deposited out of suspension progressively. However, various geological processes such as meandering, land emergence, sea level changes and

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4 Soil Mechanics: Principles and Practice mountainous erosion

coastline cliff erosion beach deposits river valleys, fluvial terraces lakes, lacustrine, flood plains, alluvium estuaries, estuarine deltas, deltaic seas, marine oceans, oceanic boulders, cobbles gravels gravels sands silts clays organics, plant remains colloids, muds, ooze, skeletal remains

Figure 1.1 Simplified deposition environment – water-borne soils

flooding tend to produce a complex mixture of different soil types.

Glacial deposits (Figure 1.2) During the Pleistocene era which ended about 10,000 years ago the polar ice caps extended over a much greater area than at present with ice sheets up to several hundred metres thick and glaciers moving slowly over the earth’s surface eroding the rocks, transporting rock debris and depositing soils of wide variety over Northern Europe, the United States, Canada and Asia.

The deposits are generally referred to as glacial drift but can be separated into: ■■ ■■

Soils deposited directly by ice; Soils deposited by melt-waters.

Soils deposited by ice These are referred to as till. Lodgement till was formed at the base of the glaciers and is often described as boulder clay. Unless the underlying rock was an argillaceous shale or mudstone, the fine fraction consists of mostly rock flour or finely ground-up debris with the proportion of clay minerals being low. Gravel, cobble and boulder-size lumps of rock are embedded in this finer matrix. These deposits have been compressed or consolidated beneath the thickness of ice to a much greater stress than at present and are overconsolidated which makes them stiff and relatively incompressible.

The deposits have been left as various landforms: oval-shaped mounds of boulder clay called drumlins are a common variety.

Ablation till was formed as debris on the ice surface and then lowered as the ice melted and typically consists of sands, gravels, cobbles and boulders with little fines present but because of their mode of formation they are less dense and more compressible. Melt-out till was formed in the same way but from debris within the ice.

Soils deposited by melt-waters These may be referred to as outwash deposits, stratified deposits or tillite. Close to the glaciers the coarser particles (boulders, cobbles, gravels) will have been deposited as ice contact deposits but streams will have provided for transport, sorting and rounding of the particles and subsequently producing various stratified or layered deposits of sands and gravels including outwash and fluvio-glacial deposits. A photograph showing the ill-sorted nature of individual glacial deposits is presented in Figure 1.2a, although some layering is evident.

As the glaciers melted and retreated, leaving many large lakes, the finer particles of clays and silts were deposited (glacio-lacustrine deposits) producing laminated clays and varved clays. In deeper waters or seas where more saline conditions existed glaciomarine deposits are found. A photograph showing the highly stratified nature of varved clays is presented in Figure 1.2b.

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Chapter 1 Soil formation and nature 5 From the soil mechanics point of view the term ‘till’ is of little use since it can describe soils of any permeability (very low to very high), any plasticity (non-plastic to highly plastic) with cohesive or granular behaviour.

Although glacial soils are often considered to be varied and mixed it may still be possible at least within a small site to identify a series of layers or beds of different soil types and it is important to attempt a reasonable geological interpretation during the site investigation.

Sand, gravel, cobbles Sharp unconformity

Sand with gravel, some cobbles

Post-depositional changes These have altered glacial and many other soils in the following ways: ■■

Fine to coarse gravel, cobbles

Beach cobbles Late glacial deposits of layered but ill-sorted sands and gravels, near Minehead, Somerset, UK.

Figure 1.2a Stratified ill-sorted glacial gravels

■■

■■

Varved clay showing annual layers in a typical glacial lake deposit, Finland with (lighter) silt and sand layers and (darker) clay layers.

Photograph courtesy of J. J. Sederholm, 1907.

(No, the man with the fine moustache is not the author!)

Figure 1.2b Mass characteristics of varved clay

■■

■■

Freezing/thawing – this tends to destroy the structure of the soil so that the upper few metres of, say, laminated or varved clays have been made more homogeneous. Associated with desiccation vertical prismatic columnar jointing has been produced in many boulder clays.

Freeze/thaw cycles during winter/summer periods produce down-slope creep. In addition, thawing of ice lenses formed during winter leaves excess water in the soil which then undergoes the process of gelifluction or solifluction, a down-slope movement. Accumulations of this type of soil, referred to as head, occur in areas beyond the ice margins, in periglacial areas.

Fissures – these may be produced in boulder clays due to stress relief on removal of ice. Where they have opened sufficiently they may be filled with other clay minerals making them much weaker or with silt and sand particles making them more permeable. Due to chemical changes they may be gleyed (reduced to a light grey or blue colour and of softer consistency).

Shear surfaces – due to moving ice shear stresses may have produced slip surfaces in the clay soil which can be grooved, especially if gravel particles are present, slickensided or polished.

Weathering – oxidation will change the colours in the upper few metres, especially of clays, and leaching of carbonates is likely.

Leaching – where this has been extensive in postglacial marine clays such as in Norway, Sweden and Canada the removal of some of the dissolved salts in the original pore water by the movement

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6 Soil Mechanics: Principles and Practice of fresh water has resulted in a particle structure which is potentially unstable. This structure can support a high void content or high moisture content (usually greater than the liquid limit) and can be fairly strong (soft, firm or stiff) when undisturbed but when it is disturbed the soil structure collapses and with the excess of water present, the soil liquefies.

During deposition a loose structure is formed but loess has reasonable shear strength and stability (standing vertically in cuts) due to clay particles binding the silt particles and to a lesser extent secondary carbonate cementation. Loess is typically buff or light brown in colour but inclusion of organic matter gives it a dark colour as in the ‘black earth’ deposits of the Russian Steppes.

The reduction in strength is called sensitivity and when the reduction or sensitivity is high the soils are referred to as quick clays, described further in ­Chapter 7.

Fossil root-holes provide greater permeability, espe­ cially in the vertical direction, than would be expected of a silt so making the soil drain more easily. However, when loess is wetted the clay binder may weaken causing collapse of the meta-stable structure and deterioration of the soil into a slurry. Therefore, loess is very prone to erosion, as illustrated in Figure 1.3.

The collapsible behaviour of this soil is described in ­Chapter 6.

Wind-blown soils Wind action is most severe in dry areas where there is little moisture to hold the particles together and where there is little vegetation or roots to bind the soil together. Wind-blown or aeolian soils are mostly sands and occur near to or originate from desert areas, coastlines and periglacial regions at the margins of previously glaciated areas.

There are basically two forms of wind-blown soils: ■■

■■

Dunes – these are mounds of sand having different shapes and sizes. They have been classified with a variety of terms such as ripples, barchan dunes, seif dunes and draas which are found in desert areas and sand-hills which are found in temperate coastal regions. They are not stationary mounds but will move according to wind speed and direction with some desert dunes moving at over 10 m/year and coastal sand-hills moving at a slower rate.

Sand sizes are typically in the medium sand range (0.2–0.6 mm) with coarser sand particles forming the smaller mounds (ripples). In coastal regions vegetation such as marram grass is promoted to bind the sand together and stabilise the dunes for coastal protection.

Loess – these deposits cover large areas and are mostly found across the Northern hemisphere from North America to China. Silt particles mixed with some sand and clay particles are stirred up by the wind to form dust-clouds which can be large and travel several thousand kilometres. For example, the loess found in Russia and central Europe is believed to have originated from the deserts of North Africa.

It can vary from a thin crust to tens of metres thick.

Soil particles Nature of particles The nature of each individual particle in a soil is derived from the minerals it contains, its size and its shape. These are affected by the original rock from which the particle was eroded, the degree of abrasion and comminution during erosion and transportation and decomposition and disintegration due to ­chemical and mechanical weathering. A discussion on ­particle size, shape and density and the tests required to ­identify these properties is given in Chapter 2.

The mineralogy of a soil particle is determined by the original rock type and the degree of alteration or weathering. Particles can be classified as: ■■ ■■

■■ ■■

Hard granular – grains of hard rock minerals, especially silicates, from silt to boulder sizes.

Soft granular – coral, shell, skeletal fragments, volcanic ash, crushed soft rocks, mining spoil, quarry waste, also from silt to boulder sizes.

Clay minerals – see below.

Plant residues – peat, vegetation, organic matter.

These are discussed in the section on soil formation, above.

Most granular particles are easy to identify with the naked eye or with the aid of a low magnification

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Chapter 1 Soil formation and nature 7

Figure 1.3 Severe erosion of loess landscape, Shaanxi Province, China (With permission from Professor Patricia Ebrey, Professor of History, University of Washington, US.)

microscope after washing off any clay particles present. The hard granular particles consist mostly of quartz and feldspars and are roughly equidimensional.

The quartz particles, in particular, have stable chemical structures and are very resistant to weathering and abrasion so these minerals comprise the bulk of silt and sand deposits. Gravel, cobble and boulder particles are usually worn-down fragments of the original rock.

Soft granular particles will produce a more compressible soil since the particles can be easily crushed and they are more likely to be loosely packed.

Clay minerals (Figure 1.4) The word clay is thought to be derived from the Old English word ‘claeg’ meaning sticky. The term ‘clay’ can have several meanings: 1. Clay soil – the soil behaves as a ‘clay’ because of its cohesiveness and plasticity even though the clay mineral content may be small.

2. Clay size – most classification systems describe particles less than 2 µm as ‘clay’ which is a reasonably convenient size. However, some clay minerals

may be greater than 2 µm (see Figure 1.4) and some soils less than 2 µm such as rock flour may not contain many clay minerals at all.

3. Clay minerals – these are small crystalline substances with a distinctive sheet-like structure producing plate-shaped particles.

Clay minerals are complex mineral structures but they can be visualised and classified at a molecular level by considering the basic ‘building blocks’ which they comprise, as shown in Figure 1.4. The octahedral and tetrahedral sheets combine to form layered units, either two-layer (1:1) or three-layer (2:1) units. The molecular structure of the more common mineral types is illustrated in Table 1.3. The octahedral sheets are not electrically neutral and therefore do not exist alone in nature.

However, the minerals gibbsite and brucite are stable.

The oxygen and hydroxyl ions dominate the mineral structure because of their numbers and their size; they are about 2.3 times larger than an aluminium ion and about 3.4 times larger than a silicate ion. Even if their negative charges are satisfied, because the O22 and OH2 ions exist on the surface of the sheets they will impart a slightly negative character.

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8 Soil Mechanics: Principles and Practice Name

Representation

silicon

tetrahedron

tetrahedral layer

oxygen

4 oxygen ions enclosing one silicon ion (silicate)

tetrahedra joined together to form a layer

Si

aluminium or magnesium

octahedron

hydroxyl

octahedral layer

Composition

6 oxygen ions or hydroxyl ions enclosing one aluminium, magnesium, iron or other ion

octahedra joined together to form a layer

Al

Minerals two-layer unit (1:1 mineral)

Al Si

1 tetrahedral and 1 octahedral layer

three-layer unit (2:1 mineral)

Si Al Si

2 tetrahedral and 1 octahedral layer

gibbsite

G

octahedral layer with 6 hydroxyls and at least 2/3 of cations being aluminium

brucite

B

octahedral layer with aluminium entirely replaced by magnesium

stack

Al Si Al Si

bonding

Figure 1.4 Clay minerals

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Chapter 1 Soil formation and nature 9 Table 1.3 Structure of clay minerals

Mineral

Layer structure

kaolinite

1:1

halloysite

1:1

illite

montmorillonite

chlorite

2:1

2:1

2:1:1

Stack structure Al or G Si Al or G Si Al or G Si Al or G Si

K

Si Al or G Si K Si Al or G Si Si Al or G Si Si Al or G Si Si Al or G Si B Si Al or G Si

If substitution of the cations has occurred, for example, Al31 for Si41 or Mg21 for Al31 because these ions were more available at the time of formation, then there will be a greater net negative charge which is transmitted to the particle surface. Isomorphous substitution refers to the situation when the ions substituted are approximately of the same size. Base-exchange or cation-exchange capacity is the ability of a clay mineral to exchange the cations within its structure for other cations and is measured in milli-equivalents per 100 grams of dry soil.

The resulting negative charges are neutralised by adsorption on the mineral surfaces of positive ions (cations) and polar water molecules (H2O) so that with various combinations of substituted cations,

K

Bonding between layers

Base exchange capacity me/100 g

hydrogen bonds (strong)

3 – 15

hydrated with water molecules

6 – 12

potassium ion 10 – 15 (weaker than hydrogen bonds)

van der Waal’s forces exchangeable ions water molecules (weak)

brucite sheet

80 – 140

20

exchangeable cations, interlayer water and structural layers or stacking a wide variety of clay mineral structures is possible.

Most clays formed by sedimentation are mixtures of kaolinite and illite with a variable amount of montmorillonite whereas clays formed by chemical weathering of rocks may also contain chlorites and halloysites.

Cation exchange is important in that the nature and behaviour of the clay minerals is altered. This can occur as a result of the depositional environment, weathering after deposition and leaching due to sustained groundwater flow. It can also be promoted by chemical stabilisation methods for engineering purposes such as the addition of lime (calcium hydroxide) to strengthen a soil for road building.

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10 Soil Mechanics: Principles and Practice

Soil structure The way in which individual particles arrange themselves in a soil is referred to as soil structure.

This structure is sometimes referred to as a soil skeleton.

Cohesive soils (Figures 1.5, 1.6 and 1.7) Clay mineral particles are too small to be seen by the naked eye so their arrangements are referred to as microstructure or microfabric and our knowledge of particle structure comes largely from electron microscope studies. The nature of the more common clay mineral types is described in Table 1.4 and some electron microphotographs of mineral structures are given in Figure 1.5.

There are two basic types of kaolinite. One is formed from chemical weathering of feldspars under hydrothermal activity producing larger well-ordered mineral grains. These are the typical china clays of

Cornwall, England. Microphotographs of this type are given in Figures 1.5a and b.

Another form is a sedimentary clay deposited under freshwater and brackish conditions having smaller particle sizes and a more disordered structure. These are the typical ‘ball clays’ of Devon and Dorset, England.

These kaolinite clays have been used for centuries in the ceramics industry.

Illite and montmorillonite have a less regular and flakier structure; examples are shown in Figures 1.5c–e.

The unusual fine tubular structure of halloysite is shown in Figure 1.5f.

Clay mineral particles have electrically charged surfaces (faces and edges) which will dominate any particle arrangement. The microstructure of clay soils is very complex but appears to be affected mostly by the amount and type of clay mineral present, the proportion of silt and sand present, the deposition environment and chemical nature of the pore water (Collins and McGown, 1974).

Collins and McGown observed a wide variety of structural forms within a number of natural, normally

Table 1.4 Nature of clay mineral particles

Mineral

Diameter: thickness ratio

Surface area m2/gram

kaolinite

10 – 20

10 – 70

Nature Hydrogen bond prevents hydration and produces stacks of many layers (up to 100 per particle).

Particle size up to 3 µm diameter, low shrinkage/swelling

halloysite

–

40

Two water layers between stacks when fully hydrated (4H 2 O) distort structure to a tubular shape. Low unit weight.

Water (in crystal) irreversibly driven off at 60–75°C affecting moisture content, classification and compaction test results

illite

20 – 50

80 – 100

Common mineral but varies in chemical composition. Particles flaky, small, diameter similar to montmorillonite but thicker.

Moderate susceptibility to shrinkage/swelling

800

High surface area due to small (<1 µm) and thin (<0.01 µm) particles produced by water molecules and exchangeable ions entering between layered units and separating them. A good lubricant. Water readily attracted to mineral causing very high susceptibility to expansion, swelling and shrinkage

montmorillonite (smectite)

200 – 400

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Chapter 1 Soil formation and nature 11

2 µm 2 µm a) Kaolinite

b) Kaolinite (Vermiform type)

2 µm

2 µm c) Illite

d) Smectite - montmorillonite

Sand particle

2 µm

Silt particle

e) Montmorillonite on silt and sand particles

f) Halloysite

Figure 1.5 Electron microphotographs of clay mineral structures (Image reproduced from the 'Images of Clay Archive' of the Mineralogical Society of Great Britain & Ireland and The Clay Minerals Society, www.minersoc.org/gallery.php?id=2)

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12 Soil Mechanics: Principles and Practice Elementary particle arrangements (Face to face groups of particles) dispersed – mostly face–face arrangement of groups

flocculated – mostly edge–face and edge–edge partly discernible – no strong structural tendency, difficult to distinguish Particle assemblages clay coatings on silt and sand particles (see Figure 1.5e)

interweaving bunches strips of clay particles interwoven around each other and around silt particles

connectors - ‘bridges’ of mostly clay particles between silt and sand particles particle matrix present where clay content is high binding other assemblages together aggregations - silt to fine sand size mixtures of elementary particle arrangements

Figure 1.6 Clay particle arrangements (From Collins and McGown, 1974)

or lightly overconsolidated soils, as illustrated in ­Figure 1.6. The engineering behaviour of clay soils (shear strength, compressibility, consolidation, permeability, shrinkage, swelling, collapse, sensitivity, etc.) will be better understood if the nature of the microstructure of the soil is appreciated.

The microstructural development of a clay–silt mixture is illustrated in Figure 1.7. The silt is from a clay-free glacial deposit and the clay is an airdried sample of London Clay. The small clay content

(19.6%) provides sufficient cohesion and plasticity but this is only due to the action of clay coatings and bridges between silt particles. At the high clay content (64%) the structure comprises a particle matrix with interweaving strands of clay particles clearly visible.

The images were taken with an environmental scanning electron microscope (ESEM) which has the advantage of examining soil structure while still moist and unaffected by any preparation techniques.

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Chapter 1 Soil formation and nature 13

100 µm

100 µm

X

V

V

V

Clay:silt ratio 30:70 Clay content 19.6%

Mostly medium, some fine silt

Note clay coatings and bridges between silt particles

100 µm X

100 µm V

X

V

X

X V

X

V

X X

V

V

X

Clay:silt ratio 60:40 Clay content 39.2% Silt particles marked by X

V

Clay:silt ratio 100:0 Clay content 64% Note interweaving strands of clay particles Voids marked by V

Figure 1.7 Silt to clay soil – clay:silt mixtures (Images prepared by Dr Patrick Hill, University of Manchester, UK)

The macrostructure of a clay soil comprises the structure which can be seen with the naked eye and generally consists of features produced during deposition such as inclusions, partings, laminations, varves and features produced after deposition such as fissures, joints, shrinkage cracks, root holes.

Water content is a commonly used parameter to represent the structural nature of a clay soil since it is related to the openness of the microstructure, provided the soil is fully saturated. If the soil is partially

saturated then void ratio, porosity or specific volume are also used.

The state of packing of a clay soil cannot be represented by a relative density approach since maximum and minimum densities cannot be sensibly defined.

The liquidity index and consistency index are parameters sometimes used to represent the structural state of a clay soil since they compare the natural moisture content with two limits, the plastic limit and the liquid limit. This is described further in Chapter 2.

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14 Soil Mechanics: Principles and Practice Name

Plan view

Elevation

Points of contact per particle

Porosity %

Void ratio

Cubic

6

47.6

0.91

Rhombic

12

26

0.35

Figure 1.8 Particle packing

Granular soils (Figure 1.8) Granular soils comprise coarse silts, sands, gravels and other coarser particles. Their soil structure will depend on: ■■ ■■ ■■ ■■

■■

The size, shape and surface roughness of the individual particles; The range of particle sizes (well graded or uniformly graded); The mode of deposition (sedimented, glacial); The stresses to which the soil has been subjected (increasing effective stresses with depth, whether the soil is normally consolidated or overconsolidated); The degree of cementation, presence of fines, organic matter, state of weathering.

The state of packing of a granular soil whether loose or dense can be visualised in a number of ways as shown in Table 1.5. The limits of packing can be illustrated by considering the void spaces within an ideal soil

consisting of equal sized spherical particles as shown in Figure 1.8. In practice, typical values of porosity lie within the limits of about 35–50%, with the lowest porosity and greatest density produced with: ■■ ■■ ■■ ■■

Larger particle sizes; A greater range of particle sizes; More equidimensional particles; Smoother particles.

The difference in porosity between the densest state and the loosest state of a granular soil is typically about 9–10%.

Because of the variables discussed above, neither porosity nor void ratio are good indicators of the state of packing so density index, ID, is often used. This term is also referred to as relative density. Density index compares the in situ or as-placed state with the loosest and densest possible states. This is described further in Chapter 2.

Table 1.5 Packing of granular particles

Effect of packing

Loose

Dense

distance between particles

furthest apart

closest together

void space

maximum (maximum e and n)

minimum (minimum e and n)

density

minimum

maximum

particle contacts

least

most

freedom of movement of particles

most

least

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Chapter 1 Soil formation and nature

15

SUMMARY A wide variety of soil particles, combinations of particles and structural arrangements is produced by geological processes in nature. Each depositional environment has its own characteristics and post-depositional processes can modify the soil dramatically.

There is a need to distinguish between coarse (granular) soils and fine (cohesive) soils as they behave differently, particularly regarding shear strength, permeability and consolidation. The electrochemical nature of clay minerals and the relationships with the pore water chemistry can have a significant bearing on the engineering behaviour of soils containing clay particles. Granular soils, from silt to boulder sizes, may comprise hard or soft particles.

The different structural arrangements of coarse soils and fine soils are described. When soils are affected by engineering structures or reworked during construction, the structural arrangement may be irretrievably altered.

A fuller understanding of the properties of a soil such as shear strength, consolidation, permeability, shrinkage, swelling, collapse and sensitivity will be gained by appreciating the nature of the particles and the structural arrangement, especially for soils in their natural state.

FURTHER READING Collins, K. and McGown, A. (1983). Micromorphological studies in soil engineering. Sixth International Meeting on Soil Micromorphology, 1, pp. 195–217.

Henkel, D. J. (1982). Geology, geomorphology and geotechnics. Geotechnique, 32 (3), pp. 175–194.

Waltham, A. C. (2009). Foundations of engineering geology. Third edition, Taylor & Francis, Abingdon, Oxfordshire.

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Index

A parameter, see pressure, parameters abutments, bridge, 387, 388 actions, 287–292, 337, 361–366, 411–423, 445, 446 active pressure, see earth pressure activity, activity index, 38, 49, 251, 427 adhesion, 225, 270, 277, 342, 343, 344, 345, 346, 347, 348, 349, 350, 362, 363, 364, 376, 378, 382, 412, 413 aeolian soils, 6 air entry value, 38, 39, 122, 124, 125, 529 air voids, 38 et seq, 51, 121, 122, 123, 231 content, 41, 51, 478, 479, 490, 491, 494, 504, 507 lines, 42, 489, 494, 503, 504 allowable bearing pressure, 269, 391 sand, 280–283, 292 allowable settlements, see foundations anchors, 386, 393, 394, 395, 396 anchored walls, see walls angle of shearing resistance clay, 116, 217, 218, 219, 220, 224, 235, 236, 237, 239, 240, 249, 250, 255, 256, 272, 273, 276, 346, 370, 371 sand, 116, 217, 218, 219, 220, 224, 225, 226, 227, 228, 229, 253, 272, 273, 276, 277, 279, 347, 348, 349, 370, 371 angular strain, 318, 333 anisotropic soil, 69, 77, 92, 100, 114, 119, 120, 145, 169, 170, 232, 311 aquicludes, 54, 92, 534 aquifers, 54, 192, 195, 528, 534 arching, 88, 89, 372, 373 area ratio, 520, 522, 523 artesian, 54, 56, 90, 91, 97, 133, 134

at rest, see earth pressure Atterberg limits, see liquid and plastic limit augering, see hand and mechanical augering axi-symmetric condition, 113, 118, 119, 210, 211, 223, 229, 233 B parameter, see pressure, parameters back pressure, 63, 64, 138, 176, 177, 234, 241, 253, 254, 255, 256 band drains, 187, 188, 189, 190, 191, 204, 473 Bangkok, Thailand, case study, 135 base-exchange, see cation-exchange basements, 220, 222, 386, 387, 388, 398 Nicoll Highway, case study, 409–410 top-down method, 387, 407–408 Tokyo, Japan, case study, 407–408 bearing capacity, see also allowable bearing pressure, piles, retaining structures base inclination factors, 274 depth factors, 273, 274 eccentric loading, 274, 275, 276, 277, 289–292 effect of compressibility, 277, 325 effect of water table, 268, 276, 282 factor of safety, 269 factors, 272–273 inclined loading, 275–276, 290–291 limit state design, see limit state design modes of failure, 270, 271, 272, 278, 279, 283, 284 net ultimate, 276, 277, 287–292 punching shear, 270, 271, 278, 279, 280, 284 safe, 269

sand over clay, 279, 280 shape factors, 273 strength cases, 275, 276 theory, 270–272 two clay layers, 278, 279 bearing pressure, 390, 391, 401, 403, 404 bedding, 24 bentonite, see montmorillonite boiling, 55, 81, 99 borehole permeability test, see permeability borehole record, 532, 533, 534, 535 boulders, 1, 4, 6, 20, 513, 514, 516 description, 20 boulder clay, see glacial clay brucite, 7, 8 bulbs of pressure, 147 bulk density, see density bulk modulus, see modulus bulking, 482, 483, 484, 485, 501, 502 cable percussion boring, see ground investigation methods California bearing ratio, 477, 493, 494, 495–496 capillaries, 57, 121, 122 capillary break, 122, 123, 140 capillary rise, 106, 121, 122, 130, 267, 436 Carsington dam, 457 cation-exchange, 9, 168, 252 cement stabilisation, 476, 497 characteristic values, see also limit state design foundations, 269, 270, 287–292 material properties, 269, 270 negative skin friction, 351, 352, 365, 366 pile load, 337, 338, 339, 340, 341, 361–366 sliding, 277, 291

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552 Index characteristic values (Continued) slope stability, 434, 435, 436, 437, 438, 439, 441, 443, 444, 445, 446, 447, 448, 451, 452, 459–468 statistical approach, 269 water table, 80, 81, 90, 97, 98, 99, 101, 102, 411, 412, 435, 436, 459, 460, 527 weight density, 435, 436, 439, 441, 443, 444, 445, 446, 506 Charity Hospital, USA, case study, 156, 358, 359 chlorite, 9 classification, 26 et seq, 34, 39 clay, see also consolidation, shear strength, bearing capacity, earthworks, walls, slope stability classification, 22, 23, 26 content, 36, 38, 236, 250, 251, 252, 427, 498, 499 cutter, 516 description, 19, 21, 22, 23, 24, 25 drainage conditions, see drainage fissured, see fissures macrostructure, 13 microstructure, 10–13 minerals, 7–10, 236 partially saturated, 236, 237, 253, 254 sensitivity, 5, 6, 195, 232, 251, 252, 307, 312, 313, 351, 427, 454 see also moisture sensitivity settlements, see settlements size, 7, 13, 29, 476 softening, 482, 483 soil, 7 stiffness, 142, 143 strength, see strength coarse soils, 17, 19, 20 cobbles, 5, 6, 19, 20, 59, 513, 514, 516 description, 20 coefficient of compressibility, 128, 177, 180, 184, 185, 189, 197, 198, 199, 201, 306, 307, 519, 527 consolidation, 171, 172, 177, 178, 179, 180, 181, 182, 184, 188, 189, 199, 200, 201, 202, 519 consolidation, in situ, 181, 186, 189, 191, 524

curvature, 29, 30, 46, 476 earth pressure, see earth ­pressures permeability, see permeability secondary compression, 177, 195, 312, 313 cofferdams, see also sheet piling base stability, 398 boiling, see boiling effect of flexibility and propping, 373 flow around, 54 flow net, 76, 78, 79, 98 piping, 54, 80, 81, 82 strutted excavations, 388, 396–398, 407–410 cohesion, undrained, see strength cohesion intercept, see strength colour, terms, 21, 22, 25 compaction air voids lines, 42, 489, 494, 503, 504 compactive effort, 475, 476, 478, 479, 485, 486, 487, 488, 489, 490, 491, 492 correction for stone content, see oversize particles density, 40, 42, 475, 476, 477, 478, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 498, 499, 502, 503, 504, 505 dynamic, 474 earth pressures due to, 384–385 factors affecting, 42, 485, 486 field, 133, 134, 475, 476, 478, 486–492, 499, 500, 503 laboratory, 476, 478, 485, 486, 488, 489, 492–495, 502, 503, 504 layer thickness, 486, 489, 492 plant, 475, 486, 487, 488, 491, 492 soil type, 476, 477, 478, 479, 481, 482, 484, 486, 491 specification, 476, 477, 478, 488–490, 503 water content, 42, 476, 478, 479, 485, 486, 489, 492, 494, 495, 499, 500, 503, 504, 505 composite soils, 21, 25 compressibility, 161 et seq, see also stiffness bearing capacity, 277 coefficient of, 128, 177, 180, 184, 185, 189, 197, 198, 199, 201, 306, 307

disturbance, 163, 164 index, 316 in situ curves, 163, 164, 165, 166 load duration, 166, 167 load increments, 166, 176 pore size distribution, 166, 167 reloading curves, 162, 163, 164, 165, 168 residual soil, 168, 169 secondary compression, 111, 112, 166, 167, 168, 171, 177, 191, 195, 311–313, 316, 319, 390 void ratio–pressure plot, 109, 111, 117, 161, 162, 163, 164, 165, 166, 167, 168, 169, 198, 305, 329, 330 compression anisotropic, 120, 169, 170, 223, 245 delayed, 111, 167, 168 isotropic, 119, 169, 225, 243, 244, 245 triaxial, 119, 120, 225 compression index, 177, 178, 195, 198, 238, 239, 305, 306 cone penetrometer, 32, 225, 313, 314, 315, 331, 339, 348, 514, 523, 524 consistency, 22, 34 consistency index, 13, 37, 49 consolidation analogy, 117, 118, 170 around piles, 343, 344, 350, 351 cell, 63, 64 coefficient of, see coefficient correction for construction period, 182, 183, 201, 202 curve-fitting, 178, 179, 180, 181, 199, 200 degree of, 179, 180, 181, 182, 184, 185, 186, 190, 199, 200, 201, 202, 203, 204 deposition, 109, 110, 111, 183, 184, 185 in situ curve, 165, 166 in triaxial test, 138, 240, 241, 242, 243 isochrones, 170–1 oedometer test, 170, 175, 176 one-dimensional theory, 170–175 primary, 171, 172, 175, 176, 179, 180 radial, 64, 176, 177, 181, 182, 187, 188, 189, 190, 191, 204

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Index 553 settlement, see settlement two- and three- dimensional, 181, 182, 187, 188, 500 constant head permeability test, see permeabitiy construction period, correction for, 182, 183, 201, 202 construction pore pressures, see ­pressure contact pressure, 140–144 contaminated soils, 2, 15 contiguous bored pile walls, see walls coring, rotary, 517, 518, 533 creep, see secondary compression crib walls, see walls critical depth, 347, 348, 365 critical hydraulic gradient, 81, 99 critical state, theory, 169, 170, 243–249 cuttings, 220, 221, 222, 429, 430, 431 see also slope stability damage to buildings, see ­settlements, permissible Darcy’s law, 58, 59, 171 deep wells, 70, 71, 72 deflection ratio, 317, 318, 319, 332, 333 deflection rule, 75, 76 delayed compression, see ­compression density, 14, 20, 30, 31 bulk, 31, 32, 41, 42, 46, 47, 106, 177 dry, 41, 42, 46, 105, 178, 478, 485, 486, 488, 489, 492, 493, 494, 495 effect of, 226, 227, 228, 229 index, 14, 31, 32, 47, 227, 228, 229 in situ, 31, 32, 488, 489, 490 maximum, 31, 32, 47 minimum, 32, 47 particle, see particle density relative, see density index weight, see weight density depth correction, 281, 302, 313, 314, 331, 357 factors, 273, 274 of exploration, 283, 284, 353, 358, 359 of foundations, see foundations description, 14, 19, 21, 22, 23, 24, 25 desiccated crust, 111, 112, 278, 279, 283, 284

desiccation, 111, 112, 125, 126 design approaches, 268, 269, 270, 435, 439, 443, 445, 446, 447, 448, 449, 459–468 allowable bearing pressure, 292 categories, 260, 261 foundations, 260 et seq, 287–292, 295, 296 Observational method, 407–408, 409–410 Reports, geotechnical, 510, 511, 531–536 site investigation, 510 et seq design values earth pressures, see earth ­pressures foundations, 269, 270, 287–292 geometrical data, 289, 290, 291 modulus, 298, 303, 304, 308 piles, 335–347, 348, 349, 350, 351, 352, 361–366 reinforced soil, 400–401, 402, 403, 404, 405, 406, 422, 423 resistance, 270, 272, 274, 277, 278, 279, 280 serviceability criterion, 268, 269, 270 sliding, 277, 291, 292 slope stability, see characteristic values uplift, 80, 81 walls, 392, 393, 394, 395, 396, 411–423 walls, surcharge, 371, 383–384, 398, 414–416 water table, 97, 98, 100, 101, 276, 282, 380, 381, 411–412 desk study, 510, 511, 512, 530, 531 dewatering, 55, 70, 71, 72, 187, 188, 189, 192, 193 diaphragm walls, see walls differential settlement, 317, 318, 319, 320, 358, 359, 402 dilatancy, 22, 214, 215, 224, 225, 226, 227, 228, 229, 231 discontinuities, 24 dispersed structure, 12 disturbance, 163, 164, 165, 192, 229, 230, 242, 303, 517, 518, 519, 520, 521 downdrag, see negative skin ­friction drainage blankets, 55, 133, 134, 473, 499, 500

drained condition, 117, 220, 221, 222, 223, 224, 230, 234, 235, 242, 243, 246, 247, 248, 257, 273, 274, 275, 276, 277, 279 gravity, 304 in hydraulic cell, 63, 64, 65 path, 117, 170, 171, 172, 173, 174, 175, 176, 177, 179, 180, 181, 182, 187, 188, 189, 190 stress change, due to, 221, 222 undrained condition, 220, 221, 222, 223, 224, 230, 231, 232, 233, 234, 236, 237, 238, 239, 240, 241. 242, 246, 254, 255, 273, 274, 275, 276, 277, 278, 279 drained, see drainage drains gravity, 304 horizontal, 186, 498, 499, 500 vertical, 187, 188, 189, 190, 191, 204, 473, 524 sand, 189 band, 187, 188, 189, 190, 191, 204, 473 drawdown, 222, 433, 449, 450 drumlins, 4 dunes, 6 durability, 477, 494 earth dams, see also slope stability, earthworks construction pore pressures, 132, 222, 499, 500 flow through, 55, 56, 83, 84 stability, 55, 56, 83, 84, 87, 88, 89, 222, 429, 430, 432, 433, 452, 453, 472, 473, 474 earth pressure active, 114, 220, 370–375, 376, 377, 378, 379, 380, 381, 382, 383, 384, 392, 393, 394, 395, 396, 397, 402–406, 411–422 at rest, 63, 114, 115, 116, 119, 128, 169, 170, 211, 216, 217, 218, 219, 220, 225, 244, 245, 346, 347, 348, 370, 371, 372, 373, 405, 527 coefficients, 376, 377, 378, 379, 382, 383, 414, 415, 416, 417 due to compaction, 384, 385 due to surface loads, 383, 384, 414, 415, 416 effect of

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554 Index earth pressure (Continued) cohesion intercept, 378, 379, 380, 413 flexibility and propping, 373, 393, 394, 395, 396 movement, 370–373 wall friction, 373, 374, 375, 376, 377, 378, 414 water table, 380, 381, 411, 412, 413, 414, 415 minimum equivalent fluid ­pressure, 379, 380 passive, 114, 220, 371, 372, 373, 374, 375, 376, 377, 378, 379, 393, 394, 395, 416, 417 undrained, 381, 382 earthworks acceptability of fill, 132, 475–479 acceptability of cohesive soils, 478, 479, 481, 496, 499, 500 acceptability of granular soils, 478, 480 bulking, 483, 484, 485, 501, 502 compactability, 478 compaction plant, 476, 486–488, 491, 492 construction plant, 472, 474, 475, 477, 478, 481, 482 efficiency, 477, 478, 481, 482 material requirements, 471, 472, 476, 477 moisture condition value, 478, 479–481, 496, 501 softening, 482, 483, 499, 500 eccentric loading, see bearing capacity, walls effective area, 273, 274, 275, 276, 277, 287, 288, 390, 391, 401, 402, 403 size, 29, 46, 59, 60, 84, 93 ejector wells, 71, 72 elevation head, see pressure embankments, 430, 432 see also earth dams, slope stability, ­earthworks stability, 220, 222, 432, 471, 472, 473, 474 engineered fill, 1, 17, see also ­earthworks equipotential lines, 72–79 equivalent fluid pressure, minimum, 379, 380 water content, 33, 34, 38, 48, see also oversize particles raft, 357

erosion, 3, 6, 55, 56, 87, 88, 89, 111, 112, 113, 114, 115, 132, 267, 268, 285, 286 internal, 80, 81 eustacy, 190–1 excavations, see also cuttings flow into, 54, 55, 78–83 stability, 54, 55, 56, 80, 81, 97, 98, 99, 386, 387, 429, 437 strutted, see cofferdams vertical cuts, 437, 438, 460 expansive soils, 127, 128, 264, 265 factor of safety, 269, 296, 303, 389, 390, 391, 395, 398, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 446, 450, 451, 452, 454, 457, 458–468 factors, partial, see partial factors failure modes, 208, 209, 214, 217, 218, 220, 222, 223, 270, 271, 272, 278, 279, 283, 284, 336, 337, 350, 351, 431, 432, 433 falling head permeability test, 62, 63, 65, 66, 93, 95 fall cone test, 230, 231, see also liquid limit falls, see slope stability fill, see acceptability, made ground filter paper method, 125 filters, 55, 84, 85, 86 fine soils, 17, 19–23 fines, 21, 29, 33, 60, 130, 476, 479, 180, 499 fissures, 5, 24, 25, 128, 129, 181, 221, 232, 235, 237, 341, 342, 397, 431, 437, 479, 486 flocculated structure, 12, 149, 150, 151, 153, 155, 156, 157, 168 flood bank, 55, 56, 83, 84, 92, 471 flows, 54, 55, see also slope stability flow lines, 54, 55, 56, 73–78 flow nets, 74–78 flow slides, 426, 428 fluvio-glacial drift, 4 foundation, see also bearing ­resistance, settlements stress distribution allowable settlement, 269, 270, 280, 281 depth, 146, 260, 261, 262, 263, 264, 265, 267, 268, 273, 274, 287, 302 effect of tree roots, see tree roots

flexible, 142, 143, 144, 145, 146, 147, 148, 182, 296, 297, 299, 333, 477 pad, 261, 262, 263 pier and beam, 261, 262 raft, 142, 143, 144, 146, 147, 148, 149, 150, 151, 152, 263, 264, 268, 280, 283, 284, 297, 299, 301, 317, 318, 319, 324, 325, 332, 333 spread, 142, 146, 147, 151, 152, 261 et seq, 295, 296, 318, 319 stiffness, 142, 143, 151, 262, 263, 264, 297, 299, 301, 302, 312, 324, 325, 332, 333, 336, 340, 352, 354 strip, 142, 143, 146, 147, 148, 149, 150, 151, 152, 155, 261, 262 freezing index, 129, 130 freezing/thawing, 5, 128, 129 frost action, 129, 130, 266, 267 frost heave test, 131 frost susceptibility, 130, 131, 267 gabion walls, see walls geogrids, 473, see reinforced soil geological origin, 24, 25 geometrical data, 287, 288, 289, 341, 383, 384, 429 geotechnical categories, 296, 433 gibbsite, 8, 9 glacial deposits, 4, 5, 235, 240, 251, 342, 343, 454, 457, 479, 483, 494, 495, 499, 500 gleying, 4 grading, see particle size ­distribution gravel, 4, 5, 6, 19, 20, 21, 122, 130, 225, 227, 229, 476, 478, 480, 483 correction for, see oversize ­particles description, 14, 19, 20, 25 frost action, 130 gravity walls, see walls ground freezing, 131, 323 ground investigation, 283, 284, 512 et seq cable percussion boring, 515, 516 contaminated land, 530, 534 depth, 283, 284, 513 extent, 512, 513 hand auger, 514, 515 in situ testing, see in situ testing mechanical auger, 516, 517 methods, 513 et seq

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

Index 555 reports, 510, 511, 531–536 sampling, see sampling ground model, 358, 510, 511, 534, 535 groundwater, see also piezometers, water table occurrence, 53, 54, 55, 56 lowering, 55, 70–72, 78, 79, 101, 185, 186, 187, 304, 322, 323, 324, 325, 351 observations, 190, 522, 527–530, 532, 533, 534, 535 removal, 186, 187, 188, 189, 190 gyttja, 18 halloysite, 9, 10, 11 hand augering, see ground ­investigation head, see pressure heave, 56, 78, 80, 82, 98, 127, 128, 129, 130, 131, 265, 266, 267, 317, 318, 344, 398, 497 horizontal displacement, 266, 297, 317, 370, 371, 372, 373 stress, see stress humus, 17, 18 Hvorslev surface, 244, 248, 249 hydraulic consolidation cell, 63–65, 176, 177 hydraulic fracture, 65, 87, 89 hydraulic gradient, 57, 58, 60, 61, 62, 64, 66, 68, 69, 70, 78, 79, 80, 81, 82, 93, 96, 171, 286 critical, 81, 99, 171 ice lenses, 128, 129, 131, 267 soils deposited by, 4 illite, 9, 10, 11, 38, 167, 192 inclined loading, see bearing capacity index tests, see liquid, plastic and shrinkage limits in situ curve, see compressibility in situ testing dilatometer test, 526, 527 Dutch cone penetrometer, 523, 524 field vane test, 524, 525 pressuremeter test, 525, 526 standard penetration test, 522, 523 instrumentation, see piezometers isochrones, 172, 173 isomorphous substitution, 7

isotropic soil, 69, 77, 114, 118, 119, 129, 144, 169, 297 Jackfield, UK, case study, 455–457 joints, see discontinuities kaolinite, 9, 10, 11, 38, 167 K0 condition, see earth pressure at rest laminated clay, 4, 24, 130, 181, 307 layered profiles, 54, 56, 60, 61, 66, 70, 78, 87, 92, 144, 151, 185, 278, 279, 280, 283, 284, 320, 339, 343, 351, 400, 407, 407, 436, 438, 527, 528, 533, 534, 535 layering, principle of, 299, 302 leaching, 5, 111, 251, 252 leaning instability, 323 levees, see flood banks lime stabilisation, 474, 476, 496, 497 limit state design, ultimate base stability, 398 boiling, 81, 99 characteristic values, see ­characteristic values correlation factors, see piles design values, see design values foundations, 268, 269, 270, 277, 287–292, 312, 318, 319, 324, 333 heaving, 78, 80, 82, 98 internal erosion, 80, 81 limit states, 209, 269, 270, 277, 318, 319 partial factors, see partial factors piles, see piles piping, 81, 82 quick condition, 81 reinforced soil, 400–406, 422, 423 sliding, 277, 291 slope stability, see slope stability uplift, 80, 81, 92, 98, 100 walls, see walls walls, surcharge, 383, 384 limit state design, serviceability, 146, 269, 270, 298, 318, 389, 390, 392, 399, 402, 403, 404 line load, 145, 384 liquidity index, 13, 37, 49, 251 liquid limit, 22, 34, 35, 36, 48, 127, 135, 185, 230, 231, 251, 306, 427, 476, 482, 499 local shear failure, 271 Lodalen, Norway, case study, 454–455

loess, 6 log-time method, see consolidation, curve fitting Los Vaqueros Dam, California, USA, case study, 472 M6 Motorway, UK, case study, 499–500 made ground, 1, 17, 25, 31, 225, 264, 514 median size, 29 Mexico City, Mexico, case study, 168, 195, 196 middle third rule, 274, 275, 390, 391 model factors, 340, 363 modulus bulk, 213 constrained, see coefficient of compressiblity drained, 119, 177, 178, 212, 308, 310, 313, 314, 315, 525, 526 effect of strain, 303, 328 increasing, 144, 297, 298, 299, 300, 301, 302, 327, 328, 357 shear, 212, 525, 526 undrained, 298, 303, 304, 307 Young’s, 144, 212, 214, 296, 297, 298 Mohr–Coulomb relationship, 217, 218, 219, 220, 225. 226, 227, 228, 229, 235, 236, 237, 240, 270 Mohr’s circle of stress, 209, 210, 211, 218, 219, 235, 236, 237, 371, 400 Mohr’s circle of strain, 212, 213 moisture condition value, see ­earthworks moisture content, see water content moisture sensitivity, 482, 483, 499, 500 monitoring, 285, 286, 318, 321, 322, 323, 357, 359, 407–408, 409–410 montmorillonite, 9, 10, 11, 38, 167, 343 mudflows, 426, 427, 428 negative skin friction, see piles normally consolidated clay, 109, 110, 111, 112, 114, 115, 116, 132, 135, 146, 162, 163, 164, 165, 167, 176, 184, 185, 195, 214,

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

556 Index normally consolidated clay (Continued) 216, 222, 236, 238, 239, 240, 241, 242, 245, 303, 304, 305, 307, 311, 431 observational method, see design oedometer test, 117, 118, 124, 130, 175, 176, 177, 178, 224, 306, 307 settlement, see settlement organic soils, see peat outwash deposits, 4 overconsolidated clay, 110–113, 114, 115, 116, 118, 119, 120, 127, 129, 135, 146, 162, 163, 164, 165, 166, 178, 198, 228, 237, 238, 239, 240, 241, 242, 247, 248, 303, 304, 305, 307, 311, 344, 345 overconsolidation ratio, 111, 112, 114, 115, 116, 120, 127, 128, 163, 198, 303, 304, 307, 345, 527 oversize particles, 33, 34, 48, 62, 225, 235, 265, 479, 489, 493, 494, 495, 499, 500, 505, 506, 507 overturning, 274, 389, 390, 391, 417, 418, 419, 420, 421 packer test, see permeability packing, state of, 14, 226, 227, 228 partial factors actions, 340 foundations, 269, 270, 287–292 groundwater, 80 heave, 97, 98, 99 negative skin friction, 351, 352 piles, 337, 338, 339, 350, 352, 361–366 sliding, 291 slope stability, see characteristic values, slope stability uplift, 80, 101, 102 walls, 395, 396, 411–423 walls, surcharge, 383, 384, 414, 415 weight density, 435, 436, 439, 441, 443, 444, 445, 446 particle clay, 7 density, 26, 27, 41, 99, 105, 178, 306, 494 effect on strength, 14, 226, 227, 228, 230

mineralogy, 6, 226, 227, 228, 229, 236 oversize, see oversize particles shape, 6, 14, 26, 27, 226, 227 size distribution, 14, 27, 28, 29, 30, 45, 46, 58, 59, 85, 135, 226, 227, 228, 476 passive pressure, see earth ­pressure peat, 3, 6, 17, 18, 25, 31, 33, 36, 92, 304, 307, 313, 473, 484, 527 classification, 18 description, 18, 25 secondary compression, see secondary compression perched water table, 54 permafrost, 128, 129, 130, 266, 267 permeability borehole tests, 65–70, 95, 96, 523, 524, 528, 529 coefficient, 58, 70, 72, 73, 74, 77, 78, 79, 93–96, 171, 172, 177, 181, 184, 185, 189, 192, 519 empirical values, 59, 60 laboratory tests, 61–65, 93, 94 layered soils, 60, 61, 94, 95 packer test, 67, 68 piezometer test, 68, 69, 96, 181 pumping test, 69, 70 triaxial, 65 typical values, 57, 59, 185 pulverised fuel ash, 1, 31, 473, 476, 497 phreatic surface, 53, 54, 55, 70, 75, 83, 431, 449, 450 piezocone, 524 piezometer, 68, 69, 187 hydraulic, 529 permeability test, 68, 69 pneumatic, 529, 530 standpipe, 528, 529, 533 vibrating wire, 530 piezometric head, 57, 58, 69, 79, 92 level, 54, 92 observations, 527 piles, 335 et seq bored, in clay, 339, 340, 341, 342, 343, 345, 346, 350, 361, 362, 363 bored, in sand, 349, 350 critical depth, 347, 348, 349, 365 driven, in clay, 343–346, 364 driven, in sand, 346–349, 358, 359, 365

factor of safety, 350, 356 layered deposits, 339, 343, 351 limit state design, 335–340, 350 correlation factors, 338, 339, 340, 361 model factors, 340, 363 load tests, 337, 338, 339, 351, 353, 358, 359, 361, 362 negative skin friction, 350–353, 359, 360, 365, 366 case study, 359–360 types, 335, 336, 337, 474 ultimate compressive resistance from static load tests, 337–340, 361, 362 from ground test results, 339–341, 362, 363, 364, 365 from other methods, 340, 341 weight of pile, 341 pile groups block failure, 336, 353, 354, 355 efficiency, 353, 354 individual pile penetration, 336, 354, 355 load variation, 344, 353 pile cap, 336, 339, 340, 353, 354, 355 serviceability limit state, 337, 340, 350, 355, 356, 357, 361 settlements, 355, 356, 357, 358, 359 spacing, 344, 352, 353, 354, 355, 358, 359 stiffness, 340, 352, 353, 354, 355, 358, 359 stressed zone, 352, 353, 358, 359 ultimate capacity, 354, 355 piping, 56, 80, 81, 82, 83 piston sampler, 520, 521 plane strain condition, 211, 212, 223, 224, 228, 229 plasticity behaviour, 26, 33, 37, 214, 215, 216, 217, 218, 238, 239, 243–248, 278, 284, 477 chart, 23, 37 index, 36, 37, 38, 116, 127, 130, 184, 195, 232, 233, 238, 239, 240, 250, 251, 252, 265, 306, 310, 476 terms, 22, 35, 481 plastic limit, 22, 34, 36, 135, 476, 479, 496, 499, 500

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

Index 557 Poisson’s ratio, 116, 119, 145, 146, 212, 214, 297, 308, 311, 356, 526 pole, 209, 210, 211, 213 polluted soils, 2 pores, 32, 38, 39, 40, 42, 43, 166, 169, 485 pore pressure, see pressure pore size distribution, 42, 43, 57, 166, 167, 169 porosity, 14, 38, 41, 51, 57 pozzolana, 500 precompression, 185, 186, 187, 188, 473 preconsolidation pressure, 110, 111, 112, 134, 163, 164, 165, 166, 167, 184, 195, 198, 216, 217, 246, 247, 305, 311, 315, 316 pressure active, see earth pressure change in pore, 116–120, 132, 138, 139, 163, 171, 172, 201, 220, 221, 222, 223, 224, 254, 307, 343, 344, 350, 359, 360, 430–433, 449, 450, 454, 478, 499, 500 construction, 133, 134, 182, 183, 432, 433, 478, 499, 500 head, 57, 58, 79, 80, 82, 92, 96, 97, 380, 381 initial pore, 113–117, 171, 172, 173 minimum and maximum, 390, 391, 417, 418, 419 minimum equivalent fluid, 379, 380 parameters, pore, 118–120, 134, 139, 221, 224, 236, 241, 253, 254, 255, 307, 449, 450 pore, 57, 98, 106–109, 112, 113, 136, 170, 171, 172, 176, 184, 187, 188, 221–224, 230, 234, 235, 236, 240, 241, 242, 369, 380, 381 pore, control methods, 70–72, 185 pore pressure ratio ru, 436, 446 uplift, 56, 80, 81, 92, 98, 100 pressuremeter test, 525, 526 principal stress, 210 propped walls, see walls pumice, 19 pumping test, see permeability quick clays, 5, 6, 251, 252, 427, 454 quick condition, 81

raft foundations, 140–144, 146–152, 155, 263, 264, 268, 280, 283, 288, 299, 324, 325 rapid drawdown, 222, 433, 449, 450 reinforced soil, 398–406, 472 construction, 398–400, 476 design, 400–406, 422, 423 reinforcement, 399, 400 relative deflection, 317, 318 relative density, see density index reports Geotechnical Design, 510, 511, 532, 534 Ground Investigation, 510, 511, 531–535 residual strength, see strength retaining structures, see earth ­pressures, walls rigid foundation, 142, 143, 151, 152 ring shear test, 224, 249, 250 risk, 260, 261, 452, 453, 510, 511, 512, 513, 530 register, 260, 261, 511 rocks, weathered, 2, 3 rollers, compaction, see compaction plant root-time method, see consolidation, curve fitting Roscoe surface, 244, 246, 248 rotary drilling, 517, 518, 533 rotation, 317, 318, 372, 373 rotational failure, 389, see also slope stability Rowe cell, see hydraulic cell running sand, 55, 92 safety margin, 209 sampling block, 5, 6 Delft continuous, 521, 522 disturbance, see disturbance groundwater, 522 piston, 519, 520, 521 quality, 518, 519, 528 split-barrel SPT, 519, 520, 522, 523, 533 thin-walled tube, 519, 520 U100, 518, 519, 520, 533 window, 522 sand allowable bearing ­pressure, 280–282, 292

bearing capacity, see bearing resistance description, 19, 20, 21, 25, 31 drains, 189 frost action, 129, 130, 131 normally consolidated, 118, 146, 314, 315, 316 overconsolidated, 118, 120, 146, 315, 316, 346, 347 parameter Af, 120 permeability, 57, 58, 59, 60, 94 replacement test, 31, 32 settlements, 161, 280, 281, 612–317 shear strength, see strength stiffness, 142, 143, 146, 224, 225, 314, 315, 372 saprolite, 3 saturation back pressure, 64, 65, 138, 177 capillary rise, 106, 121, 122 degree of, 41, 42, 50, 51, 120, 123, 178, 485, 504 line, see air voids lines partial, 38, 39, 41, 105, 106, 118, 119, 120, 121, 122, 123, 124, 236, 237 process, 241, 242, 253, 254 triaxial, 241, 242, 253 zone of, 106, 121, 124 Schoharie Creek, USA, case study, 285, 286 scoria, 19 scour, see erosion secant bored pile walls, see walls secondary compression, see compressibility sedimentation test, 27, 29 seepage anisotropic soils, 69, 77, 92, 100 deflection rule, 75, 76 effect on slope stability, 434, 435, 436 flow nets, 74–78, 79 force, 80, 81, 111 pressure, 81, 98 quantities, 77, 78, 79, 96, 98 theory, 72–74 selected materials, 1, 471, 472, 473, 476, 477 sensitivity, see clay serviceability, see limit state design settlement, see also piles

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

558 Index settlement, consolidation, 304–307, 321, 324 compression index, 177, 178, 195, 198, 305, 306, 329 oedometer, 178, 197, 198, 306, 307, 329 time, 161, 167, 172, 173, 178, 182–187, 188, 189, 190, 191, 201, 202 settlement, immediate, 296, 298–303, 326–328 average, 301 depth correction, 302, 327 during construction, 182, 183, 298, 310, 311 elastic displacement theory, 297–298 modulus estimates, 303, 304 modulus increasing, 297–302, 327, 328 principle of layering, 299, 302, 327 principle of superposition, 299, 301, 326 rigidity correction, 299, 301, 302, 328 yielding, 296, 303, 328 settlements, permissible, 317–320 allowable, 268, 312, 313, 317 criteria for movements, 296, 318 damage criterion, 280, 318, 319, 333, 358 definitions, 317, 318 routine limits, 318, 319, 320 settlements, regional, 192–196, 304, 305, 321, 322, 323 settlements, sand, 161, 312–317 Burland and Burbridge method, 315, 316, 332 Schmertmann method, 314, 315, 331, 332 settlements, secondary, 296, 311–313 coefficient, see coefficient general method, 312, 313 settlements, total, 296, 307–311 elastic displacement theory, 297–298 elastic drained method, 308, 309, 310, 330 modulus, drained, 310, 330 Skempton-Bjerrum method, 307–308, 329, 330 settlements, piles individual piles, 350, 360, 361

pile groups, 355, 356, 357, 358, 359 rigidity correction, 299, 301, 302, 328 shape factor, 65, 66, 67, 78, 98, 273, 314 shear box test, see strength shear modulus, see modulus shear surfaces, 5, 218, 226, 428, 456 sheet piling, see also cofferdams anchored or propped, 386, 393, 394, 395, 396 boiling, 54, 55, 56, 81, 99 cantilever, 381, 382, 383, 386, 391–393, 394, 395, 421, 422 heaving, 56, 78, 80, 82, 97, 98 piping, 56, 80, 81, 82 seepage, 76, 77, 78, 79, 81, 96 shell and auger, see cable ­percussion boring shell fragments, 6 shrinkage, 38, 39, 43, 50, 264, 265, 266, 317, 483, 484, 485, 501 shrinkage limit, 34, 38, 39, 40 sieving, see particle size ­distribution silt, 19, 21, 22, 25, 27, 29, 31, 33, 37, 59, 87, 88, 89, 122, 128, 130, 131, 227, 316, 527 site investigation, 510 et seq desk study, 510, 511, 512, 531 ground investigation, see ground investigation site reconnaissance, 511, 512, 530, 532 skin friction, 80, 101, 277, 339, 345, 346, 347, 348, 349, 373–378, 414 see also piles, negative skin friction slickensided surfaces, 5, 24, 283, 284, 428, 487 slides, see slope stability sliding, 274, 277, 291, 389, 390, 391, 419, 420 slope stability, see cuttings, earth dams, embankments Bishop simplified method, 442–446, 460, 461, 462, 463, 464 circular arc, 431, 432, 433, 438 et seq circular arc, undrained, 438, 439 critical circle, 439, 440, 454, 455, 461, 462, 463, 464

dry slope, 435, 446, 447, 448, 449, 458 effective stress, 435, 436, 437, 441 et seq, 454–456, 458–462 factor of safety, see factor of safety case study, Nicolet landslide, Canada, 427 first-time slides, 429, 430, 431, 454–455 mass movement, 427, 428, 429, 430, 431, 432, 433 method of slices, 438–448, 460–468 natural slopes, 426–429, 454–457 non-circular, 433–436, 450, 451, 452, 454 overdesign factor, 439, 441, 443–448, 462–468 plane translational slide, 433–436, 455, 456, 457, 458, 459 pore pressure ratio, 436, 445, 446 pre-existing slip surfaces, 428, 452, 456, 457 progressive failure, 428, 429, 430, 431 rapid drawdown, 433, 449, 450 serviceability, 452, 453 stability coefficients, 439, 440, 441, 446, 447, 448, 462, 463 stability number, 435, 436, 449, 450 submerged slopes, 435, 436, 449, 450 tension crack, 437, 438, 439, 440 three-dimensional, 454, 455 undrained, 430, 432, 437, 438–441, 460, 462 vertical cuts, 437, 438, 460 water table, 429–437, 445–452, 454, 455, 456–462, 464 wedge method, 451, 452 smectite, see montmorillonite softening, 341, 342 soil aeolian, 6 classification, 26 et seq, 49 colour, 21 description, 16 et seq, 532, 533, 534, 535 extraction method, 323 formation, 1–6 gassy, 185 glacial, see glacial deposits

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

Index 559 marine, 3, 5, 183 model, 39, 40, 41, 42, 50, 121, 485 moisture, 106, 121, 122 nailing, 399 residual, 168, 169, 215 section, 534, 535 stiffness, 142, 143, 146, 297, 303, 304, 310, 314, 315, 496, 497 strength terms, 22, 23 structure, 10–14, 24, 181, 182, 251, 252 tropical, 3, 36 solum, 3 specific gravity, see particle density specific volume, 41, 169 spread foundations, see foundations stability coefficients, see slope stability stability number excavations, 397, 398 slopes, undrained, 439, 440, 441 standard penetration test, 31, 224, 280, 281, 282, 292, 310, 314, 315, 316, 332, 339, 348, 519, 520, 522, 523, 533 standpipe, 527, 528 standpipe piezometer, 527, 528, 529, 533 stiffness, see foundations, modulus stone, see gravel strain control, 223, 224, 225, 226, 232, 233, 234, 243 effect of, 214, 215, 216 normal, 211, 212, 213 rate of, 223, 224, 232, 234, 242, 243 reinforced soil, 405 representation of, 211–214 shear, 211, 212, 213, 214, 223, 226 volumetric, 171, 177, 178, 212, 213, 214, 257 yield, see yield strength critical state, 214, 215, 217, 227, 228, 229, 245, 246, 243–249, 250, 257 dry, 22 effect of drainage, 220–223 effective stress, clay, 217–224, 236, 237, 241, 242, 344, 345, 346, 434, 435, 436, 437, 441

failure criterion, 214–218 failure mode, 218, 220, 222 peak, 195, 214, 215, 217, 218, 219, 220, 225–230, 241, 246, 253, 378 residual, 214, 215, 217, 224, 249, 250, 430, 455, 456, 457 ring shear test, 224, 249, 250 sand, 224–229, 273, 274, 276, 277, 279 shear box test, 224, 225, 226, 227, 253 test procedures, 239, 240 triaxial, see triaxial test ultimate, 214, 215, 253 undrained, clay, 23, 112, 184, 216, 221, 223, 224, 229–233, 234–239, 254, 255, 273, 275–279, 303, 304, 310, 339, 341, 342, 343, 344, 345, 354, 355, 378, 381, 382, 397, 398, 399, 437, 438, 439, 479, 481, 482, 483, 524 vane, see vane test variation with depth, 238, 239 yield, 214, 215, 216, 217 stress effective, 105–108, 109–115, 117, 119, 123, 124, 134–137, 162–165, 169–172, 184, 188, 305 et seq, 360 et seq, 434–437, 441 et seq effective, above water table, 123, 124, 140 history, 109–112, 162–168, 238, 239 horizontal, 113–116, 119, 120, 134, 137, 144, 170, 346, 347, 349, 384, 385, see also earth pressures in the ground, 105 et seq paths, 114, 219, 220, 243–249, 255, 256 principal, 113–116, 118, 119, 209, 210, 211 shear, 209, 210, 211, 225, 226, 227, 228 total, 30, 105–107, 108–111, 113, 114, 117, 118, 119, 120, 138, 139 stress distribution bulbs of pressure, 147, 283, 284, 352, 353

circle, 146, 147, 148, 149, 151, 182 line load, 145 Newmark’s method, 147, 149, 156 on walls, see earth pressure point load, 143, 144, 145, 158, 261, 384 principle of superposition, 147, 149, 152, 156, 158 rectangle, flexible, 144, 146, 147–152, 156, 157, 182 rectangle, rigid, 142, 143, 144, 151, 152, 158 strip load, 146–149, 150, 151, 152, 182 triangular load, 151, 152, 153, 158 uniform pressure, 143, 144, 146–153, 181, 182 structure, 10–14, 24, 181, 182, 251, 252 structure, mass, 23, 24, 219, 231, 232 submerged density, 81, 82, 99, 108, 109, 136, 435, 436 slopes, 436 subsidence, 192–196, 304 suction, 106, 121, 122, 123, 124–125, 126, 127, 264, 265, 266, 436 sump pumping, 54, 70, 71 super-elevation, 268 superposition, principle, 147, 149, 152, 156, 158 surcharging, 185, 186, 187, 188, 189, 201, 202 surface area, 10 swelling, 127, 128, 162, 165, 169, 305, 306, 482, 483, 484 swelling index, 128, 177, 178, 238, 239, 305, 306 swelling pressure, 127, 128 Tancred Pit Borehole, Yorkshire, case study, 90 temperature, effect of, 18, 36, 58, 59, 128–131, 264, 265, 266, 267, 496 tension cracks, 378, 379, 382, 383, 437, 438, 439, 440 Teton Dam, USA, case study, 87–89 thixotropy, 111, 168, 195, 252 till ablation, 4 lodgement, 4 melt-out, 4

Copyrighted material – 9781137512208

Copyrighted material – 9781137512208

560 Index tilt, 275, 283, 284, 317, 318, 319, 321–323 time factor, 171–175, 178–181, 184, 187, 199, 200, 202, 204 topsoil, 18, 472, 473, 476, 484 toughness, 22 Tower of Pisa, Italy, case study, 321–323 Transcona Elevator, Canada, case study, 283–285 translational slides, see slope stability trees, effects of, 125, 126, 127, 265, 266 trial pits, 460, 513, 514 triaxial test compression, 118, 119, 138, 223, 224, 233–236 consolidated drained, 222, 224, 231, 242–243, 257 consolidated undrained, 119, 120, 224, 231, 240–242, 254–256 extension, 119, 120, 220, 223, 224 multi-stage, 236 permeability, 65 quick undrained, 221, 222, 224, 231–235 rate of strain, 234, 241, 242, 243 saturation, 140, 236, 237, 241, 253, 254 tropical soils, 3, 36 tuff, 19 unconfined compression test, 231 undisturbed samples, see sampling undrained, see drainage, shear strength uniformity coefficient, 29, 30, 227, 228, 476 unit weight, see weight density uplift, 56, 77, 80, 81, 82, 98, 100 Usk dam, UK, case study, ??

vane test, field, see in situ tests vane test, laboratory, 224, 230, 231, 232, 233 varved clay, 5, 24, 59, 60, 181, 191, 232 Venice, Italy, case study, 192–194 voids, see pores void ratio, 31, 41, 51, 109, 111, 117, 122, 161–169, 171, 172, 177, 178, 197, 228, 305, 306, 504 constant, 226–229 volcanic soil, 17, 19, 36, 195 walls adhesion, see adhesion anchored, propped, 373, 391, 393, 394, 395, 396 basement, 386, 387, 388 cantilever, 373, 419, 420, see sheet piling cofferdam, see cofferdams contiguous bored pile walls, 386, 391, 392 crib, 386, 388 diaphragm, 386, 391, 392 embedded, see sheet piling friction, 373–376, 377, 378 gabion, 386, 388 gravity, 386, 389, 391, 417–421 masonry, 386, 387 reinforced concrete, 386, 387, 391 reinforced soil, see reinforced soil secant bored pile walls, 386, 391, 392 sheet pile, see sheet piling waste materials, see made ground water-borne soils, 3, 4 water content, 13, 32, 33, 37, 41, 42, 177, 427, 457 optimum, 478, 485, 489, 492, 493, 495, 499

Copyrighted material – 9781137512208

water table, 53, 54, 56, 66, 68, 69, 90, 91, 92, 105–109, 111, 112, 121–126, 135, 136, 268, 276, 282, 349, see also earthworks, compaction capillary rise above, 106, 112, 121, 122, 123, 124, 126, 129 correction, 276–282 effective stresses above, 112, 123, 124, 140 effect on bearing capacity, 268, 276, 282, 287, 288, 321, 322 effect on earth pressures, 380, 381, 382, 411, 412, 413, 414 effect on slope stability, see slope stability instruments for, see groundwater observations on borehole record, 533 on soil section, 535 weathering chemical, 2, 36, 251, 252 clay, 24, 59, 111, 112, 252 grades, 2, 3, 24 mechanical, 2 oxidation, 5 wedge method active thrust, 374, 375 passive thrust, 375, 376 reinforced soil, 400, 401, 404, 405, 406 weight density, 30, 31, 32, 41, 46, 106, 107 wellpoints, 71 Westergaard material, 145 wind-blown soils, 6 yield, 135, 146, 214, 215, 216, 217, 297, 303, 311 yield stress, 135, 214, 215, 216, 217 Young’s modulus, see modulus