9780230 579804 01 Pre - macmillanihe.com · 1 Soil formation and nature 1 Objectives 1 ... Present...

Preface xiiList of symbols xivNote on units xixList of case studies xx

1 Soil formation and nature 1

Objectives 1Soil formation 1

Man-made soils 1Contaminated and polluted soils 2Naturally occurring soils 2In situ soils – weathered rocks 2In situ soils – peat 3Water-borne soils 3Glacial deposits 4Wind-blown soils 6

Soil particles 6Nature of particles 6Clay minerals 8

Soil structure 10Cohesive soils 10Granular soils 13

Summary 13

2 Soil description and classification 14

Objectives 14Soil description 14

Soil categories 14Made ground 14Organic soils 15Volcanic soil 15Particle size fractions – fundamental basis 16Very coarse soil 16Coarse soil 17Fines 18Composite soils 18

Fine soil 19Mass structure 21Degree of weathering 22Geological origin 22

Soil classification 22Particle density 23Particle shape 24Particle size distribution 24Grading characteristics 27Density 28Density Index 29Moisture content or water content 30Atterberg limits 31Activity Index 35Shrinkage limit 36Soil model 36

Summary 39Worked examples 39Exercises 46

3 Permeability and seepage 47

Objectives 47Permeability 47

Introduction 47Groundwater 47Flow problems 48Flow into excavations 48Flow around cofferdams 48Dewatering 48Flow through earth structures 49Stability problems – ‘running sand’ 49Boiling or heaving in cofferdams 49Piping 50Heaving beneath a clay layer 50Uplift pressures 50Soil voids 50Pressure and head 51

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Darcy’s law 51Effect of temperature 52Empirical correlations for k 52Layered soils 54Laboratory test – constant head permeameter 55Laboratory test – falling head permeameter 56Laboratory test – hydraulic cell – vertical

permeability 57Laboratory test – hydraulic cell – horizontal

permeability 58Laboratory test – triaxial cell – vertical

permeability 58Borehole tests – open borehole 58Borehole tests – packer tests 61Borehole tests – piezometers 62Pumping tests 63

Seepage 63Seepage theory 63Flow nets 66Flow net construction 67Seepage quantities 69Total head, elevation head and pressure head 70Pore pressure and uplift pressure 71Failure by uplift (buoyancy) 71Seepage force 72Quick condition, boiling and internal erosion 72Critical hydraulic gradient 73Failure by internal erosion 73Failure by heave – sheet piling 73Failure by piping 74Seepage through earth dams 74Seepage through flood banks, levees 74Soil filters 76

Summary 78Case studies 79Worked examples 83Exercises 94

4 Effective stress and pore pressure 97

Objectives 97Total stress 97Pore pressure below the water table 97Effective stress 98Effective stress in the ground 98Stress history 98

Normally consolidated clay 98Overconsolidated clay 101Desiccated crust 103Present state of stress in the ground 103Mohr’s circle of stress 104In situ horizontal and vertical stresses 104Changes in stress due to engineering

structures 108Pore pressure parameters – theory 110Pore pressure parameters A and B 111Capillary rise above the water table 112Effective stresses above the water table 114Desiccation of clay soils 115Suctions 116Frost action in soils 118Frost heave test 120Permafrost 121Ground freezing 121

Summary 122Case study 123Worked examples 125Exercises 130

5 Contact pressure and stress distribution 132

Objectives 132Contact pressure 132

Contact pressure – uniform loading 132Contact pressure – point loading 133

Stress distribution 134Stresses beneath point load and line

load 134Assumptions 134Stresses beneath uniformly loaded areas 136Bulbs of pressure 137Stresses beneath a flexible rectangle 137Principle of superposition 137Stresses beneath flexible area of any shape 137Stresses beneath a flexible

rectangle – finite soil thickness 137Stresses beneath a rigid rectangle 139Embankment loading 141

Summary 143Worked examples 144Exercises 149

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6 Compressibility and consolidation150

Objectives 150Introduction 150Compressibility 150

Void ratio/effective stress plot 150Reloading curves 151Preconsolidation pressure σp' and

overconsolidated ratio OCR 152Casagrande method for σp' 152Effect of sampling disturbance 153In situ curve for normally consolidated clay 153In situ curve for overconsolidated clay 153Effect of load increments 154Effect of duration of load 154Effect of secondary compressions 155Isotropic compression 156Anisotropic compression 156

Consolidation 157Terzaghi theory of one-dimensional

consolidation 157Solution of the consolidation equation 159Isochrones 159Average degree of consolidation 160Oedometer test 162Coefficient of consolidation, cv – root time

method 164Coefficient of consolidation, cv – log time

method 166In situ cv values 167Rowe consolidation cell 167Two- and three-dimensional consolidation 169Correction for construction period 170Precompression by surcharging 171Radial consolidation for vertical drains 172


7 Shear strength 190

Objectives 190Introduction 190Stresses and strains in soils 191

Representation of stresses 191Pole 191Principal stresses 191

Axial symmetry 192Plane strain 192K0 condition 192Normal and shear strains 192Mohr circle of strain 194Volumetric strains 194

Shear strength 194Effect of strain 194Idealised stress–strain relationships 197Yield and plasticity 197Flow rule and normality 198Failure criterion 199Failure of soil in the ground 199Stress paths 201Effects of drainage 202Test procedures 205

Shear strength of sand 206Stress–strain behaviour 206Shear box test 207Effect of packing and particle nature 208Constant volume condition 210Effect of density 210

Shear strength of clay 211Effect of sampling 211Undrained cohesion, cu 211Strength index tests 211Strength tests 212Laboratory vane test 212Fall cone test 212Unconfined compression test 212Field vane test 213Triaxial test 214Triaxial unconsolidated undrained (UU) test 216Multi-stage (UU) test 217Effect of clay content and mineralogy 218Partially saturated clays 218Fissured clays 218Variation with depth 219Frictional characteristics 221Test procedures 221Triaxial consolidated undrained (CU) test 222Triaxial consolidated drained (CD) test 224

Critical state theory 224Parameters 225State boundary surface 225Isotropic normal consolidation line (ICL) 225K0 normal consolidation line (K0 CL) 227Critical state line (CSL) 227

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Roscoe surface 228Tension cut-off 229Hvorslev surface 229The elastic wall 230Real soils 231

Residual strength 231Summary 233Case study 234Worked examples 236Exercises 241

8 Geotechnical Eurocodes 243

Objectives 243Relevant Eurocodes 243Personnel 243Geotechnical Design Report 243Geotechnical Risk 244Durability 245Geometrical data 245Limit states 246Verification of limit states 247Design by prescriptive measures 247Design by experimental models and

load tests 247Observational method 247Design by calculation 248Models and model factors 248Actions 248Design situations and values of actions 248Characteristic and representative values of

actions 249Design values of actions 249Effects of actions Ed 249Design resistances 249Design approach and partial factors 249Characteristic values of geotechnical

parameters 251Summary 254

9 Shallow foundations – stability 255

Objectives 255Shallow foundations 255

Definition 255Spread foundations 255Types of foundation 256Depth of foundations 259

Foundation design 263Design requirements 263Traditional approach compared with the

Eurocodes 264Bearing resistance 264

Modes of failure 264Bearing capacity and bearing resistance 266Shape factors 267Depth factors 267Base inclination factors 267Bearing resistance – overturning 268Eccentric loading 268Inclined loading 270Different soil strength cases 270Effect of water table 271Net ultimate bearing capacity 271Effect of compressibility of soil 271Sliding 271

Allowable bearing pressure of sand 272Introduction 272Settlement limit 272Allowable bearing pressure 272Corrected SPT N values 273


10 Shallow foundations – settlements 287

Objectives 287Introduction 287Are settlement calculations required? 288

Immediate settlement 289General method 289Principle of superposition 290Principle of layering 290Rigidity correction 290Depth correction 291Average settlement 291Modulus increasing with depth 291Effect of local yielding 292Estimation of undrained modulus Eu 294

Consolidation settlement 295General 295Compression index Cc method 296Oedometer modulus Eoed or mv method 297

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Total settlement 298Skempton–Bjerrum method 298Elastic drained method 299Estimation of drained modulus E' 299Proportion of immediate to total settlement 299

Secondary compression 302Introduction 302General method 302Estimation of Cα or εα values 303

Sands 304Methods of estimating settlements 304Schmertmann’s method 304Burland and Burbridge’s method 306

Permissible settlements 307Definitions of ground and foundation

movement 307Criteria for movements 309Routine settlement limits 309


11 Pile foundations 326

Objectives 326Pile foundations 326

Introduction 326Types of pile 326Loading conditions 326Uncertainty of design calculation methods 327Limit states 328Pile load tests 328Ultimate compressive resistance from

static load tests 329Ultimate compressive resistance from

ground test results 330Ultimate compressive resistance from

other methods 330Weight of pile 331

Bored piles in clay 332End bearing resistance qb 332Adhesion ca 332

Driven piles in clay 334End bearing resistance qb 334Adhesion ca – installation effects 334Adhesion ca – values 334Effective stress approach for adhesion 336

Driven piles in sand 336Effects of installation 336End bearing resistance qb 337Critical depth 337Skin friction fs 339

Bored piles in sand 340Mobilisation of base and shaft loads 340Downdrag (negative skin friction) 341

Causes of downdrag 341Determination of downdrag 342

Pile groups 342Stiffness of pile cap and structure 342Pile spacing 342Stressed zone 343Load variation 343Efficiency 343Ultimate capacity 344Settlement ratio 345Settlement of pile groups 347


12 Lateral earth pressures and retaining structures 360

Objectives 360Lateral earth pressures 360

Introduction 360Effect of horizontal movement 360Effect of wall flexibility and propping 364Effect of wall friction 364Coulomb theory – active force 365Coulomb theory – passive force 366Limitations of the Coulomb theory 366Earth pressure coefficients 367Effect of cohesion intercept c' 369Minimum equivalent fluid pressure 369Effect of water table – gravity walls 370Effect of water table – embedded walls 371Undrained conditions 372Earth pressures – undrained condition 372Tension cracks 373Uniform surcharge 373Line loads and point loads 374Earth pressures due to compaction 374

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Retaining structures 376Introduction 376Basement walls 376Bridge abutments 379Gabions and cribwork 379

Design of gravity walls 379Serviceability limit states 379Ultimate limit states 379Loss of overall stability 380Overturning or rotational failure 380Bearing pressure under the toe 380Bearing capacity 381Sliding 382Failure of structural elements 382

Design of embedded walls 382Cantilever embedded walls – general 383Cantilever embedded walls – design 383Single anchor or propped embedded walls

– general 384Single anchor or propped embedded walls

– design 384Design methods 384Gross pressure method 384Net available passive resistance method 385Factor on strength method 385BS8002 method 386Anchorages for embedded walls 386

Strutted excavations and cofferdams 387Introduction 387Strut loads 387Base stability of excavations 388Base stability – shallow excavations 388Base stability – deep excavations 389

Reinforced soil 389Reinforced soil walls – construction 389Effects of reinforcement 390Reinforced soil walls – design 390External stability 391Internal stability – general 392Tensile rupture 393Pull-out resistance or adherence 393Internal stability – tie-back wedge method 394Coherent gravity method 395


13 Slope stability 417

Objectives 417Natural and artificial slopes 417

Introduction 417Types of mass movement 417Natural slopes 417Artificial slopes or earthworks 420Short-term and long-term conditions 421

Methods of analysis 425Plane translational slide – general 425Plane translational slide – Eurocode

approach 425Plane translational slide – special cases 426Stability of vertical cuts 428Circular arc analysis – general 429Circular arc analysis – undrained condition

or φu = 0° analysis 429Tension crack 430Undrained analysis stability charts –

Taylor’s method 431Effective stress analysis 432Effective stress analysis – method of

slices 432Bishop simplified method 433Bishop simplified method – limit state

approach 434Pore pressure ratio ru 435Stability coefficients – ru method 435Stability coefficients – water table method 438Submerged slopes 439Rapid drawdown 439Non-circular slip surfaces 440Wedge method – single plane 441Wedge method – multi-plane 441Factors affecting stability and slope design 443


14 Earthworks and soil compaction 462

Objectives 462Earthworks 462

Introduction 462Construction plant 462

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Purpose and types of materials 463Material requirements 466Suitability of fill material 466Suitability of granular soils 467Suitability of cohesive soils 468Moisture condition test 469Efficiency of earthmoving 471Material problems 471Softening 471Bulking 472

Soil compaction 474Factors affecting compaction 474

Field compaction 476Compaction plant 476Specification of compaction 478Control of compaction in the field 480

Laboratory compaction 482Light compaction test 482Heavy compaction 483Vibrating hammer 483Air voids lines 484Correction for oversize particles 484California Bearing Ratio (CBR) test 484Addition of lime 485Cement stabilisation 486

Summary 487Case study 488Worked examples 490Exercises 497

15 Site investigation 499

Objectives 499Site investigation 499

Introduction 499Relationship with geotechnical design 500Stages of investigation 501Desk study 501Site inspection 501

Ground investigation 501Extent of the ground investigation 501Depth of exploration 502Choice of method of investigation 503Methods of ground investigation 504Undisturbed sampling – sampling quality 508Types of samples 509Methods of in situ testing 512Dilatometer tests 515Groundwater observations 516Investigation of contaminated land 519

Ground investigation report 520Presentation of geotechnical information 520Factual report 520Geotechnical evaluation 522

Summary 525

Answers to Exercises 526Glossary 528References 530Index 540

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

Soil formationSoils in the engineering sense are either naturallyoccurring or man-made. They are distinguished fromrocks because the individual particles are not suffi-ciently bonded together.

Man-made soilsThese are described as made ground or fill (BREDigest 427:1998). The main types of made groundare:

● waste materials● selected materials.

Waste materialsThese include the surplus and residues from construc-tion processes such as excavation spoil and demoli-tion rubble, from industrial processes such as ashes,slag, PFA, mining spoil, quarry waste, industrial by-products and from domestic waste in landfill sites.

They can be detrimental to new works through beingsoluble, chemically reactive, contaminated, haz-ardous, toxic, polluting, combustible, gas generating,swelling, compressible, collapsible or degradable.

All waste materials should be treated as suspectbecause of the likelihood of extreme variability andcompressibility (BRE Digest 427: Part 1). Thesedeposits have usually been randomly dumped andany structures placed on them will suffer differentialsettlements. There is also increasing concern aboutthe health and environmental hazards posed by thesematerials.

Selected materialsThese are materials that have none or very few ofthe detrimental properties mentioned above. Theyare spread in thin layers, are well compacted andmay be referred to as engineered fill (BRE Digest427: Part 3). This gives a high shear strength andlow compressibility, to provide adequate stabilityand ensure that subsequent volume changes and set-tlements are small.

They are used to form a range of earth structuressuch as highway embankments and earth dams,

1

Soil formation and nature

Objectives

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

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

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

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backfilling around foundations, behind retainingwalls and in reinforced soil.

Contaminated and polluted soilsDue to past industrial activities many sites com-prising naturally occurring soils have been contam-inated (there are potential hazards) or polluted (there are recognisable hazards) by the careless orintentional introduction of chemical substances.These contaminants could comprise metals (arsenic,cadmium, chromium, copper, lead, mercury, nickel,zinc), organics (oils, tars, phenols, PCB, cyanide) ordusts, gases, acids, alkalis, sulphates, chlorides andmany more compounds.

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

Naturally occurring soilsThe two groups of naturally occurring soils are those formed in situ and those transported to theirpresent location. There are two very different typesof soils formed in situ: weathered rocks and peat.

Transported soils are moved by the principal agentsof water, wind and ice although they can also beformed by volcanic activity and gravity.

In situ soils – weathered rocksWeathering produces the decomposition and disinte-gration of rocks. Disintegration is produced largelyby mechanical weathering, which is most intense incold climates and results in fragmentation or fractureof the rock and its mineral grains. Chemical alter-ation results in decomposition of the hard rock min-erals to softer clay minerals and is most intense in ahot, wet climate such as in the tropics.

Weathering gradually converts rock to a soil. BSEN ISO 14689-1:2003 requires that the weatheringprofile is described in terms of three units: rock ➤

rock and soil ➤ soil. The scale of weathering of rockmasses from this BS is given in Table 1.1.

BS EN 14689-1 states that the weathered products,which could be sand from a sandstone or clay from amudstone, can be described as a matrix and the lessweathered remnants of rock described as lithorelicsor corestones. At the mass scale the distribution andproportion of the corestones vs. matrix should berecorded. With more intense weathering the matrix (a

2 Soil Mechanics – Principles and Practice

Unit Grade Term Description

SOIL

ROCKANDSOIL

ROCK

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.

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 frameworkor as corestones.

Discolouration indicates weathering of rock material and discontinuity surfaces.

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

5

4

3

2

1

0

Residual soil

Completely weathered

Highly weathered

Moderately weathered

Slightly weathered

Fresh

TABLE 1.1 Mass weathering grades (From BS EN ISO 14689-I:2003)

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soil) would provide a continuous framework and theprinciples of soil mechanics could apply, notablystrength, stiffness and permeability.

The soil/rock interface will depend on the extentof this framework, or the proportion and extent ofthe matrix, and on the engineering application, asshown in Table 1.2.

In situ soils – peatPeats are almost entirely organic matter, comprisingpartly decomposed and fragmented plant remains.They constitute 5 to 8% of the land surface of theearth (Mesri and Ajlouni, 2007).

They are referred to as cumulose soils and mayoccur as high or moor peats comprising mostlymosses, raised bogs consisting of sphagnum peat andlow or fen peat composed of reed and sedge peat.Moor and bog peats tend to be brown or dark brown incolour, fibrous and lightly decomposed while fen peatsare darker, less fibrous and more highly decomposed.

Landva and Pheeney (1980) suggested a suitableclassification for peats based on genera, degree ofhumification, water content and the content of finefibres, 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 firstremoved from their original locations or eroded andthen transported. During these processes the parti-cles are also broken down or abraded into smallerparticles. The most erosive locations are in thehighland or mountainous regions and upper reachesof rivers, especially during flood conditions, andalong the coastline, particularly at high tides andduring storms. Cliff erosion can produce a widevariety of particles sorted into beach materials(sands, gravels) and finer materials which arecarried out to sea.

Soils deposited by water tend to be named accord-ing to the deposition environment as shown inFigure 1.1, e.g. marine clays. Whether a particle canbe lifted into suspension depends on the size of theparticle and the water velocity, so that further down-stream in rivers where the velocity decreases certainparticles tend to be deposited out of suspension pro-gressively. However, various geological processessuch as meandering, land emergence, sea levelchanges and flooding tend to produce a complexmixture of different soil types.

1 ■ Soil formation and nature 3

TABLE 1.2 Soil/rock interface

soil/rock interface 1From BS EN ISO 14689-1:2003 2After Anon (1990b)

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Glacial deposits (Figure 1.2)During the Pleistocene era which ended about10,000 years ago the polar ice caps extended over amuch greater area than at present with ice sheets upto several hundred metres thick and glaciers movingslowly over the earth’s surface eroding the rocks,transporting rock debris and depositing soils of widevariety over northern Europe, the United States,Canada and Asia.

The deposits are generally referred to as glacialdrift but can be separated into:

● soils deposited directly by ice● soils deposited by melt-waters.

Soils deposited by iceThese are referred to as till. Lodgement till wasformed at the base of the glaciers and is oftendescribed as boulder clay. Unless the underlying rockwas an argillaceous shale or mudstone the fine frac-tion consists of mostly rock flour or finely ground-updebris with the proportion of clay minerals being low.Gravel, cobble and boulder-size lumps of rock areembedded in this finer matrix. These deposits havebeen compressed or consolidated beneath the thick-ness of ice to a much greater stress than at presentand are overconsolidated which makes them stiff andrelatively incompressible. The deposits have been leftas various landforms: oval-shaped mounds of boulderclay called drumlins are a common variety.

Ablation till was formed as debris on the icesurface and then lowered as the ice melted and typi-

cally consists of sands, gravels, cobbles and boulderswith little fines present but because of their mode offormation they are less dense and more compress-ible. Melt-out till was formed in the same way butfrom debris within the ice.

Soils deposited by melt-watersThese may be referred to as outwash deposits, strati-fied deposits or tillite. Close to the glaciers thecoarser particles (boulders, cobbles, gravels) willhave been deposited as ice contact deposits butstreams will have provided for transport, sorting androunding of the particles and subsequently produc-ing various stratified or layered deposits of sandsand gravels including outwash and fluvio-glacialdeposits. A photograph showing the ill-sorted natureof individual glacial deposits is presented in Figure1.2a; although some layering is evident.

As the glaciers melted and retreated, leaving manylarge lakes, the finer particles of clays and silts weredeposited (glacio-lacustrine deposits) producinglaminated clays and varved clays. In deeper watersor seas where more saline conditions existed glacio-marine deposits are found.

A photograph showing the higly stratified natureof varved clays is presented in Figure 1.2b.

From the soil mechanics point of view the term‘till’ is of little use since it can describe soils of anypermeability (very low to very high), any plasticity(non-plastic to highly plastic) with cohesive or gran-ular behaviour. Although glacial soils are often con-


gravels

mountainouserosion

river valleys, fluvial terraces flood plains, alluvium lakes, lacustrine,

estuaries, estuarinedeltas, deltaic

coastlinecliff erosion

beach deposits

seas, marine oceans, oceanicboulders, cobbles

gravelssands

siltsclaysorganics, plant remains

colloids, muds, ooze,skeletal remains

FIGURE 1.1 Simplified deposition environment – water-borne soils

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sidered to be varied and mixed it may still be possi-ble at least within a small site to identify a series oflayers or beds of different soil types and it is impor-tant to attempt a reasonable geological interpretationduring the site investigation.

Post-depositional changesThese have altered glacial and many other soils inthe following ways:

● Freezing/thawing – this tends to destroy thestructure of the soil so that the upper few metresof say, laminated or varved clays have been mademore homogeneous. Associated with desiccationvertical prismatic columnar jointing has beenproduced in many boulder clays.

Freeze/thaw cycles during winter/summerperiods produce down-slope creep. In addition,thawing of ice lenses formed during winterleaves excess water in the soil which then under-goes the process of gelifluction or solifluction, adown-slope movement. Accumulations of thistype of soil, referred to as head, occur in areasbeyond the ice margins, in periglacial areas.

● Fissures – these may be produced in boulderclays due to stress relief on removal of ice.Where they have opened sufficiently they may befilled with other clay minerals making themmuch weaker or with silt and sand particlesmaking them more permeable. Due to chemicalchanges they may be gleyed (reduced to a lightgrey or blue colour and of softer consistency).

● Shear surfaces – due to moving ice, shear stressesmay have produced slip surfaces in the clay soilwhich can be grooved, especially if gravel parti-cles are present, slickensided or polished.

● Weathering – oxidation will change the coloursin the upper few metres, especially of clays, andleaching of carbonates is likely.

● Leaching – where this has been extensive inpost-glacial marine clays such as in Norway,Sweden and Canada the removal of some of thedissolved salts in the original pore water by themovement of fresh water has resulted in a parti-cle structure which is potentially unstable. Thisstructure can support a high void content or highmoisture content (usually greater than the liquidlimit) and can be fairly strong (soft, firm or stiff)


FIGURE 1.2A Stratified ill-sorted glacial gravels

Late glacial deposits of layered but ill-sorted sandsand gravels, near Minehead, Somerset.

Varved clay showing annual layers in a typical glaciallake deposit in Finland with thick silt and sand layersand thin clay layers.Photograph courtesy of J. J. Sederholm, 1907.(No the man with the fine moustache is not theauthor!)

FIGURE 1.2B Mass characteristics of varved clay

Sand, gravel, cobbles

Sharp unconformity

Sand with gravel, some cobbles

Fine to coarse gravel, cobbles

Beach cobbles

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when undisturbed but when it is disturbed thesoil structure collapses and with the excess ofwater present the soil liquefies. The reduction instrength is called sensitivity and when the reduc-tion or sensitivity is high the soils are referred toas quick clays.

Wind-blown soilsWind action is most severe in dry areas where thereis little moisture to hold the particles together andwhere there is little vegetation or roots to bind thesoil together. Wind-blown or aeolian soils are mostlysands and occur near to or originate from desertareas, coastlines and periglacial regions at themargins of previously glaciated areas.

There are basically two forms of wind-blown soils:

● Dunes – these are mounds of sand having differ-ent shapes and sizes. They have been classifiedwith a variety of terms such as ripples, barchandunes, seif dunes and draas, which are found indesert areas, and sand-hills, which are found intemperate coastal regions. They are not station-ary mounds but will move according to windspeed and direction with some desert dunesmoving at over 10 m/year and coastal sand-hillsmoving at a slower rate. Sand sizes are typicallyin the medium sand range (0.2–0.6 mm) withcoarser sand particles forming the smallermounds (ripples). In coastal regions vegetationsuch as marram grass is promoted to bind thesand together and stabilise the dunes for coastalprotection.

● Loess – silt mixed with some sand and clay parti-cles is stirred up by the wind to form dust-cloudswhich can be large and travel several thousandkilometres. For example, the loess found inRussia and central Europe is believed to haveoriginated from the deserts of North Africa. Loessdeposits cover large areas of the earth’s surfaceespecially the United States, Asia and China.

During deposition a loose structure is formedbut loess has reasonable shear strength and sta-bility (standing vertically in cuts) due to clay par-ticles binding the silt particles and to a lesserextent secondary carbonate cementation. Loess istypically buff or light brown in colour but inclu-sion of organic matter gives it a dark colour as in

the ‘black earth’ deposits of the Russian Steppes.Fossil root-holes provide greater permeabilityespecially in the vertical direction than would beexpected of a silt so making the soil drain moreeasily. However, when loess is wetted the claybinder may weaken causing collapse of the meta-stable structure and deterioration of the soil intoa slurry. Therefore, loess is very prone to erosionon shallow slopes.

Soil particlesNature of particlesThe nature of each individual particle in a soil isderived from the minerals it contains, its size and itsshape. These are affected by the original rock fromwhich the particle was eroded, the degree of abra-sion and comminution during erosion and trans-portation, and decomposition and disintegration dueto chemical and mechanical weathering. A discus-sion on particle size, shape and density and the testsrequired to identify these properties is given inChapter 2.

The mineralogy of a soil particle is determined bythe original rock mineralogy and the degree of alter-ation or weathering. Particles can be classed 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 forma-tion, above.

Most granular particles are easy to identify with thenaked eye or with the aid of a low magnificationmicroscope after washing off any clay particlespresent. The hard granular particles consist mostly ofquartz and feldspars and are roughly equidimen-sional. The quartz particles, in particular, have stablechemical structures and are very resistant to weath-ering and abrasion so these minerals comprise thebulk of silt and sand deposits. Gravel, cobble andboulder particles are usually worn-down fragmentsof the original rock.


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Name Representation Composition

tetrahedron

tetrahedral layer

oxygen

silicon 4 oxygen ions enclosing one silicon ion(silicate)

terahedra joined together to form a layer

Minerals

octahedron

octahedral layer

aluminium ormagnesium

hydroxyl

Al

6 oxygen ions or hydroxyl ions enclosingone aluminium, magnesium, iron or other

octahedra joined together to form a layer

Si

brucite Boctahedral layer with aluminium entirelyreplaced by magnesium

gibbsite Goctahedral layer with 6 hydroxyls andat least 2/3 of cations being aluminium

two-layer unit(1:1 mineral)

1 tetrahedral and 1 octahedral layerSiAl

three-layer unit(2:1 mineral)

2 tetrahedral and 1 octahedral layerSiAlSi

stack bondingSiAl

SiAl

6 oxygen ions or hydroxyl ions enclosingone aluminium, magnesium, iron or otherion

FIGURE 1.3 Clay minerals

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Soft granular particles will produce a more com-pressible soil since the particles can be easilycrushed and they are more likely to be looselypacked.

Clay minerals (Figure 1.3)The word clay is thought to be derived from the OldEnglish word ‘claeg’ meaning sticky. The term‘clay’ can have several meanings:

1. Clay soil – the soil behaves as a ‘clay’ because ofits cohesiveness and plasticity even though theclay mineral content may be small.

2. Clay size – most classification systems describeparticles less than 2 µm as ‘clay’ which is a rea-sonably convenient size. However, some clayminerals may be greater than 2 µm (see Figure1.4a) and some soils less than 2 µm such as rockflour may not contain many clay minerals at all.

3. Clay minerals – these are small crystalline sub-stances with a distinctive sheet-like structure pro-ducing plate-shaped particles.

Clay minerals are complex mineral structures butthey can be visualised and classified at a molecularlevel by considering the basic ‘building blocks’


MineralLayer

structureStack structure

Bonding betweenlayers

Baseexchangecapacityme/100 g

kaolinite 1:1hydrogen bonds

(strong)3 – 15

halloysite 1:1hydrated with water

molecules6 – 12

Al or GSi

Al or GSi

Al or GSi

Al or GSi

montmorillonite 2:1

van der Waal’s forces

(weak)

exchangeable ionswater molecules

80 – 140

chlorite 2:1:1 brucite sheet 20

illite 2:1potassium ion

(weaker than hydrogen bonds)10 – 15

Al or GSi

Si

Al or GSi

SiK K K

Al or GSi

Si

Al or GSi

Si

Al or GSi

Si

Al or GSi

SiB

TABLE 1.3 Structure of clay minerals

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which they comprise, as shown in Figure 1.3. Theoctahedral and tetrahedral sheets combine to formlayered units, either two-layer (1:1) or three-layer(2:1) units. The molecular structure of the morecommon mineral types is illustrated in Table 1.3.The octahedral sheets are not electrically neutral andtherefore do not exist alone in nature. However, theminerals gibbsite and brucite are stable.

The oxygen and hydroxyl ions dominate themineral structure because of their numbers and theirsize; they are about 2.3 times larger than an aluminiumion and about 3.4 times larger than a silicate ion. Evenif their negative charges are satisfied, because the O2–

and OH– ions exist on the surface of the sheets theywill impart a slightly negative character.

If substitution of the cations has occurred, forexample Al3+ for Si4+ or Mg2+ for Al3+, becausethese ions were more available at the time of forma-tion then there will be a greater net negative chargewhich is transmitted to the particle surface.Isomorphous substitution refers to the situation whenthe ions substituted are approximately of the samesize. Base-exchange or cation-exchange capacity is

the ability of a clay mineral to exchange the cationswithin its structure for other cations and is measuredin milli-equivalents per 100 grams of dry soil.

The resulting negative charges are neutralised byadsorption on the mineral surfaces of positive ions(cations) and polar water molecules (H2O) so thatwith various combinations of substituted cations,exchangeable cations, interlayer water and structurallayers or stacking, a wide variety of clay mineralstructures is possible.

Most clays formed by sedimentation are mixturesof kaolinite and illite with a variable amount ofmontmorillonite whereas clays formed by chemicalweathering of rocks may also contain chlorites andhalloysites.

Cation exchange is important in that the nature andbehaviour of the clay minerals are altered. This canoccur as a result of the depositional environment,weathering after deposition and leaching due to sus-tained groundwater flow. It can also be promoted bychemical stabilisation methods for engineering pur-poses such as the addition of lime (calcium hydrox-ide) to strengthen a soil for road building.


NatureMineral

kaolinite

halloysite

illite

montmorillonite(smectite)

10 – 70

40

80 – 100

800

Surfacearea

m /gram2

lubricant. Water readily attracted to mineral causing very highsusceptibility to expansion, swelling and shrinkage

Hydrogen bond prevents hydration and produces stacks ofmany layers (up to 100 per particle).Particle size up to 3 µm diameter, low shrinkage/swelling

distort structure to a tubular shape. Low unit weight.Water (in crystal) irreversibly driven off at 60 – 75°C affectingmoisture content, classification and compaction test results

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

High surface area due to small (<1 µm) and thin (<0.01 µm)particles produced by water molecules and exchangeable ionsentering between layered units and separating them. A good

Two water layers between stacks when fully hydrated (4H O)2

Moderate susceptibility to shrinkage/swelling

Diameter:thickness

ratio

10 – 20

–

20 – 50

200 – 400

TABLE 1.4 Nature of clay mineral particles

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Soil structureThe way in which individual particles arrange them-selves in a soil is referred to as soil structure. Thisstructure is sometimes referred to as a soil skeleton.

Cohesive soils (Figures 1.4 and 1.5) Clay mineral particles are too small to be seen by thenaked eye so their arrangements are referred to asmicrostructure or microfabric and our knowledge ofparticle structure comes largely from electron micro-scope studies. The nature of the more common clay


FIGURE 1.4 Electron microphotographs of clay mineral structures(From ‘Images of Clay’, courtesy of the Mineralogical Society and the Clay Minerals Society)

f) Halloysite

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Particle assemblages

clay coating

on silt and sand particles (see Figure 1.4e)

connectors‘bridges’ of mostly clay particles betweensilt and sand particles

particle matrixpresent where clay content is high bindingother assemblages together

aggregationssilt to fine sand size mixtures of elementaryparticle arrangements

interweaving bunchesstrips of clay particles interwoven aroundeach other and around silt particles

Elementary particle arrangements

dispersed – mostly face-face arrangement of groups

flocculated – mostly edge-face and edge-edge

partly discernible – no strong structuraltendency, difficult to distinguish

Face to face groups of particles arranged as:

FIGURE 1.5 Clay particle arrangements (From Collins and McGown, 1974)

dispersed – mostly face–face arrangements of groups

flocculated – mostly edge–face and edge–edge

particle matrixpresent where clay content is high, binding other assemblages together

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mineral types is described in Table 1.4 and someelectron microphotographs of mineral structures arepresented in Figure 1.4.

There are two basic types of kaolinite. One isformed from chemical weathering of feldspars underhydrothermal activity producing larger well-orderedmineral grains. These are the typical China clays ofCornwall, England. Microphotographs of this typeare presented in Figures 1.4a and b.

Another form is a sedimentary clay depositedunder freshwater and brackish conditions havingsmaller particle sizes and a more disordered struc-ture. These are the typical ‘ball clays’ of Devon andDorset, England. These kaolinite clays have beenused for centuries in the ceramics industry.

Illite and montmorillonite have a less regular andmore flaky structure, examples are shown in Figures1.4c – e. The unusual fine tubular structure of hal-loysite is shown in Figure 1.4f.

Clay mineral particles have electrically chargedsurfaces (faces and edges) which will dominate anyparticle arrangement. The microstructure of claysoils is very complex but appears to be affectedmostly by the amount and type of clay mineralpresent, the proportion of silt and sand present, thedeposition environment and chemical nature of thepore water (Collins and McGown, 1974).

These authors have observed within a number ofnatural, normally or lightly overconsolidated soils awide variety of structural forms as illustrated inFigure 1.5. The engineering behaviour of clay soils(shear strength, compressibility, consolidation, per-meability, shrinkage, swelling, collapse, sensitivity,etc.) will be better understood if the nature of themicrostructure of the soil is appreciated.

The macrostructure of a clay soil comprises thestructure which can be seen with the naked eye andgenerally consists of features produced during depo-


Rhombic

Cubic

Name Plan view Elevation Points of contactper particle

6

12

Porosity%

47.6

26

Void ratio

0.91

0.35

FIGURE 1.6 Particle packing

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

TABLE 1.5 Packing of granular particles

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sition such as inclusions, partings, laminations,varves and features produced after deposition suchas fissures, joints, shrinkage cracks, root holes.

Moisture content is a commonly used parameterto represent the structural nature of a clay soil sinceit is related to the openness of the microstructure,provided the soil is fully saturated. If the soil is par-tially saturated then void ratio, porosity or specificvolume are also used.

The state of packing of a clay soil cannot be rep-resented by a relative density approach sincemaximum and minimum densities cannot be sensi-bly defined. The liquidity index and consistencyindex are parameters sometimes used to representthe structural state of a clay soil since they comparethe natural moisture content with two limits, theplastic limit and the liquid limit. This is describedfurther in Chapter 2.

Granular soils (Figure 1.6)Granular soils comprise coarse silts, sands, gravelsand other coarser particles. Their soil structure willdepend on:

● the size, shape and surface roughness of the indi-vidual particles

● the range of particle sizes (well graded or uni-formly graded)

● the mode of deposition (sedimented, glacial)● the stresses to which the soil has been subjected

(increasing effective stresses with depth, whetherthe soil is normally consolidated or overconsoli-dated)

● the degree of cementation, presence of fines,organic matter, state of weathering.

The state of packing of a granular soil whetherloose or dense can be visualised in a number of waysas shown in Table 1.5. The limits of packing can beillustrated by considering the void spaces within anideal soil consisting of equal sized spherical particlesas shown in Figure 1.6. In practice, typical values ofporosity lie within the limits of about 35–50% withthe lowest porosity and greatest density producedwith:

● larger particle sizes● a greater range of particle sizes● more equidimensional particles● smoother particles.

The difference in porosity between the denseststate and the loosest state of a granular soil is typi-cally about 9–10%.

Because of the variables discussed above, porosityor void ratio are not good indicators of the state ofpacking so density index, ID, is often used. This termis also referred to as relative density. Density indexcompares the in situ or as placed state with theloosest and densest possible states. This is describedfurther in Chapter 2.


Summary

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

There is a need to distinguish between granular soils and cohesive soils as they behave differently, particu-larly regarding shear strength, permeability and consolidation. The electrochemical nature of clay mineralsand the relationships with the pore water chemistry can have a significant bearing on the engineeringbehaviour of soils containing clay particles. Granular soils, from silt to boulder sizes, may comprise hard orsoft particles.

The different structural arrangements of cohesive soils and granular soils are described. When soils areaffected by engineeering structures or reworked during construction the structural arrangement may be irre-trievably altered.

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

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A parameter, see pressure,parameters

abutments, bridge, 377actions, 244, 246, 247, 248, 249,

250, 251, 279–281, 341, 352,357

active pressure, see earth pressure activity, activity index, 35, 36, 44,

234, 410adhesion, 207, 266, 272, 330, 332,

333, 334, 335, 336, 354, 367,369, 373, 405, 406

aeolian soils, 6air entry value, 113, 117air voids, 36–38, 113, 115, 213

content, 38, 45, 479, 493, 494, 496

lines, 478, 484, 492, 493allowable bearing pressure, 264, 381

sand, 272 et seq, 284, 287allowable settlements, see

foundationsanchors, 341, 377, 384, 386angle of shearing resistance

clay, 199, 201, 206, 217, 218, 221,222, 224, 231, 232, 238, 267,268, 270, 271

sand, 199, 201, 206, 207, 208,209, 210, 211, 236, 267, 268,270, 271, 272, 336, 337, 338,339, 340, 361

angular strain, 308, 323anisotropic soil, 63, 68, 70, 83, 91,

97, 106, 110, 156, 157, 213, 301aquicludes, 47, 83aquifers, 48, 176, 179, 517arching, 80, 81, 364

area ratio, 510artesian, 47, 48, 82, 83, 88, 123, 124at rest, see earth pressureAtterberg limits, 22, 31, 32, see also

liquid limit and plastic limitaugering, 503, 504, 505–507, see

also hand augeringaxi-symmetric condition, 104, 110,

192, 193, 205, 210, 214

B parameter, see pressure,parameters

back pressure, 57, 58, 127, 168, 215,223, 237, 239

band drains, 173, 186–187base-exchange, see cation-exchangebasements, 202, 204, 347, 377, 378

case study, Nicholl Highway,400–401

case study, Tokyo, Japan, 398–399top-down method, 377–378,

398–399bearing capacity, see also allowable

bearing pressure; piles;retaining structures

base inclination factors, 267, 268depth factors, 267, 268eccentric loading, 268, 269,

281–283effect of compressibility, 271, 316effect of water table, 263, 271, 274factor of safety, 264factors, 266, 267inclined loading, 266, 269, 270,

282–283limit state design, see limit state

design

modes of failure, 264, 265, 266,276, 277

net ultimate, 271, 280–283punching shear, 265safe, 264shape factors, 267, 268strength cases, 270, 271theory, 265–267, 276vertical load only, 266–268, 277,

bedding, 21bentonite, see montmorilloniteboiling, 49, 72, 73, 83, 91borehole permeability test, see

permeabilityborehole record, 82, 521, 523boulder clay, 123boulders, 1, 4, 6, 16, 17, 53, 504

description, 17, 18brucite, 7, 8bulbs of pressure, 137bulk density, see densitybulk modulus, 194bulking, 472–474, 490, 491

cable percussion boring, see groundinvestigation, methods

capillaries, 51, 112, 113capillary break, 129capillary rise, 99, 112, 113, 114, 129,

262, 427Categories, geotechnical, 244–245,

288, 443cation-exchange, 9, 102, 155, 235CBR, 466, 484–485cement stabilisation, 465, 486, 487characteristic values, 249, 250, 252,

see also limit state design

540

Index

9780230_579804_20_Idx.qxd 6/9/10 1:39 pm Page 540

foundations, 279, 280, 281, 282material properties, 249, 250,

251negative skin friction, 342, 356,

357pile load, 329, 330, 331, 352, 353,

354, 355, 356sliding, 272slope stability, 425, 426, 427, 428,

430, 432, 433, 434, 435, 438,441, 442, 443, 450, 455, 456

statistical approach, 250, 253water table, 72, 73, 82, 88, 89, 90,

92, 93, 402, 426, 450, 517weight density, 426, 427, 495

Charity Hospital, USA, case study,145, 349

chlorite, 8classification, 14 et seq, 15, 17, 23,

44clay, see also consolidation; shear

strength; bearing capacity;earthworks; walls; slopestability

classification, 20, 22, 34content, 32, 33, 35, 218, 232, 234,

410 description, 17, 19, 20, 22, 23drainage conditions, see drainagefissured, see fissuresminerals, 7, 8, 9, 10, 218partially saturated, 218, 223, 236sensitivity, 5, 6, 179, 213, 214,

234, 298, 303, 418, 445, 446,see also moisture sensitivity

settlements, see settlementssize, 8, 15, 27, 465softening, 471–472soil, 8stiffness, 132, 133 strength, see strength

coarse soil, 14, 16, 17, 18cobbles, 5, 6, 16, 17, 53, 504

description, 18coefficient of

compressibility, 117, 118, 163,164, 167, 169, 173, 180, 181,182, 297, 298

consolidation, 158, 159, 163, 164,165, 166, 167, 169, 170, 173,174, 175, 182, 183

consolidation, in situ, 166, 167,172

curvature, 27, 28, 40, 465earth pressure, see earth pressurepermeability, 51, 52, 54–61, 158,

167, 173, 182, 184secondary compression, 163, 179,

302, 303cofferdams, see also sheet piling

base stability, 388–389boiling, see boilingeffect of flexibility and propping,

364flow around, 48flow net, 68, 89piping, 49, 73, 74, 89strutted excavations, 381–388,

398–399, 400–401cohesion, undrained, see strengthcohesion intercept, see strength,

effective stress or drained, claycolour, terms, 18, 19, 21compaction

air voids lines, 478, 479, 484, 492,493

compactive effort, 465, 474, 475,476, 479, 481, 482

correction for stone content, seeoversize particles

density, 467, 474, 475, 478, 479,483, 484, 491, 492, 494, 495

earth pressures due to, 374–375factors affecting, 474–476field, 124, 465, 476, 478, 479,

480, 481, 493laboratory, 465, 474, 475, 478,

482, 483, 491, 492layer thickness, 479, 480 moisture content, 43, 51, 465, 467,

468, 474, 478, 479, 480, 483,488, 491, 492, 493, 484, 495

plant, 465, 476–477, 479, 480, 481soil type, 465, 476specification, 465, 467, 478, 479

composite soils, 18, 19, 27

compressibility, 150 et seqcoefficient of, 117, 158, 163, 164,

165, 169, 173, 180, 297, 298disturbance, 153in situ curves, 153, 154index, 306load duration, 154,155load increments, 154reloading curves, 151, 152, 155,

156secondary compression, 155, 156void ratio–pressure plot, 99, 101,

102, 109, 150, 151, 152, 153,154, 155, 156, 157, 176, 296,320

compressionanisotropic, 110, 206isotropic, 110, 156, 207, 225, 226,

227triaxial, 110, 207

compression index, 163, 164, 179,180, 181, 219, 296–297

cone penetrometer, 30, 207, 304,305, 321, 330, 338, 503,513–514

consistency, 20, 32consistency index, 9, 13, 31, 32, 35,

44consolidation

analogy, 109, 157around piles, 341, 342cell, 56, 57coefficient of, 158, 159, 163, 164,

165, 166, 167, 169, 173, 174,175

correction for construction period,170–171, 185–186, 187

curve-fitting, 164–167, 182, 183degree of, 159, 160, 161, 162, 165,

166, 172, 173, 174, 184, 185,186, 187

deposition, 99, 100, 101, 102in situ curve, 153–154in triaxial test, 127, 223isochrones, 159, 160oedometer test, 157, 162–164one-dimensional theory, 157–159,

160

Index 541

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consolidation (continued)primary, 151–162, 164, 165, 166radial, 59, 168, 172–175, 186–187settlement, see settlementtwo- and three-dimensional, 169,

488construction pore pressures, see

pressurecontact pressure, 132 et seqcontaminated soils, 2, 15 contiguous bored pile walls, see

wallscreep, see secondary compression crib wall, see wallscritical depth, 337–339, 356critical hydraulic gradient, 73, 91critical state, theory, 156, 157, 224 et

seqcuttings, 202, 203, 204, 420, 421,

422, see also slope stability

damage to buildings, see settlements,permissible

deflection ratio, 308, 309, 310, 323

deflection rule, 68, 69delayed compression, 103, 154, 155,

156, 179density, 12, 13, 28, 29, 41

bulk, 28, 37, 38, 40, 41, 98, 100,163

dry, 28, 38, 40, 41, 163, 467effect of, 210in situ, 29, 42index, 9, 13, 18, 20, 29, 30, 42,

209, 210, 211, 271maximum, 12, 27, 29, 42 minimum, 12, 29, 42particle, see particle densityrelative, see density, indexweight, see weight density

depthcorrection, 191, 299, 300, 304,

347factors, 267, 268of exploration, 276, 349of foundations, see foundations

description, 14 et seq

desiccated crust, 103, 104, 276desiccation, 102, 115, 116Design

Approaches, 250–251, 435, 450,451, 455, 456

allowable bearing pressure, 284by calculation, 248by experimental models and load

tests, 247by prescriptive measures, 247by tests, 247foundations, 263 et seq, 279–284,

287, 288observational method, 247,

398–399, 400–401Reports, geotechnical, 243–244,

500, 520site investigation, 500–501situations, 248

design valuesactions, 247, 249, 250earth pressures, 249foundations, 279, 280, 281, 282geometrical data, 246, 249geotechnical parameters, 246, 249,

252ground resistance, 246modulus, 289piles, 329, 330, 331, 340, 341,

352, 353, 354reinforced soil, 391, 392, 393,

394, 395resistance, 247, 249, 250serviceability criterion, 247sliding, 271–272, 283–284slope stability, 425, 426, 427, 428,

430, 432, 433, 435, 438, 441,442, 443, 450, 455, 456

uplift, 72, 73walls, 385, 386, 402–408walls, surcharge, 373, 374water table, 88, 89, 90, 92, 93,

249, 370, 371, 402, 405desk study, 501, 519, 520, 522dewatering, 48, 49, 83, 171diaphragm walls, see wallsdifferential settlement, 308, 309,

310, 349, 392

dilatancy, 19, 196, 197, 207, 208,209, 210, 211, 213, 336

discontinuities, 21, 22dispersed structure, 11disturbance, 153, 176, 211, 224, 294,

508downdrag, see piles; negative skin

frictiondrainage

blankets, 49, 124, 464, 488, 489drained condition, 109, 203, 204,

205, 206, 211, 215, 221, 224gravity, 295, 371in hydraulic cell, 58, 59path, 157, 159, 160, 161, 165, 166,

167, 168, 169, 172stress change, due to, 109, 204undrained condition, 20, 202–207,

211, 213, 215, 221drained, see drainagedrains

band, 173, 186–187horizontal, 172sand, 172vertical, 172–175, 186–187

drawdown, 204, 424drumlins, 4dunes, 6durability, 245

earth dams, see also slope stability;earthworks

construction pore pressures, 123,124, 204

flow through, 49, 74, 75stability, 74, 76, 204, 421, 424,

443, 464earth pressure

active, 106, 361, 363, 367, 370,372, 383, 384, 385, 402–407

at rest, 57, 104, 105, 106, 107, 108,110, 117, 126, 127, 156, 157,192, 193, 200, 201, 202, 207,226, 227, 336, 337, 339, 340,360–361, 363, 395, 396, 516

coefficients, 361, 362, 365, 366,367, 368, 369, 372, 373, 374,375, 391, 402

542 Index

9780230_579804_20_Idx.qxd 6/9/10 1:39 pm Page 542

due to compaction, 374–375due to surface loads, 373, 374,

375, 405, 406effect of cohesion intercept, 369,

370, 405, 406effect of flexibility and propping,

364, 378effect of movement, 360–364

effect of wall friction, 364–368,374, 405, 406

effect of water table, 366, 370,404, 405

minimum equivalent fluidpressure, 369

passive, 106, 362, 363, 366, 370,380, 383, 384, 385, 407, 408

undrained, 372, 373earthworks

acceptability of cohesive soils,466, 468, 469, 471, 485, 488

acceptability of fill, 123, 465, 466acceptability of granular soils,

466, 467bulking, 472–474, 490, 491compactability, 467compaction plant, 465, 467,

476–478, 479, 480, 481construction plant, 462, 463, 468,

469, 471, 473, 488efficiency, 462, 467, 469, 471material requirements, 460, 463,

464, 465MCV, 467, 469–471, 486, 490softening, 471–472

eccentric loading, see bearingcapacity; walls

effectivearea, 268, 269, 270, 381, 391, 394size, 27, 40, 52, 53, 54, 84, 114

elevation head, see pressure embankments, see also earth dams;

slope stability; earthworks;stress distribution

stability, 202, 204, 421, 423, 488engineered fill, 1, 14, 253equipotential lines, 65, 66, 67, 68,

70, 71

equivalent fluid pressure, minimum, 369moisture content, 31, 43raft, 347

erosion, 3, 50, 83, 101, 102, 125,262, 277, 278, 307

internal, 72, 73eustacy, 177excavations, see also cuttings

flow into, 48, 83stability, 49, 83, 88, 388, 389, 420strutted, see cofferdamsvertical cuts, 428–429, 451

expansive soils, 116, 117, 118

factor of safety, 249, 250, 264, 294,301, 319, 380, 381, 382, 384,385, 389

factors, partial, see limit state designfailure modes, 190, 200, 202, 246,

247, 250, 262, 264, 266, 276,277, 327, 419, 420, 421

fall cone test, 211, 212, see alsoliquid limit

falling head permeability test, 56, 57,84, 86

fill, see earthworks, acceptability offill; made ground

filter paper method, 117filters, 49, 74, 76, 77fine soil, 14, 17, 18, 19, 20, 21fines, 17, 18, 27, 31, 77, 465, 466fissures, 5, 21, 22, 23, 119, 167, 203,

213, 214, 217, 218–219, 332,334, 372, 428

flexible foundation, 132, 133, 134,136, 137, 138, 139, 140, 146,169, 289, 323

flocculated structure, 11flood bank, 49, 74, 75, 83flow lines, 48, 49, 65, 66, 67, 68,

70flow nets, 66, 67, 68, 69, 70, 74flow rule and normality, 198, 199flow slides, 421flows, 48fluvio-glacial drift, 4foundations, see also bearing

capacity; settlements; stressdistribution

allowable settlement, 264, 272depth, 136, 255, 257, 259, 260,

261, 264, 291effect of tree roots, see trees,

effects ofpad, 257, 258pier and beam, 256raft, 132, 133, 137, 139, 140, 145,

255, 258, 277, 290, 309, 315,323, 342

spread, 132, 137, 141, 255, 276,288, 309

stiffness, 132, 133, 134, 139, 141,145, 247, 255, 258, 291, 315,316, 323, 329, 331, 342

strip, 136, 137, 140, 256–257freezing index, 118, 119freezing/thawing, 5frost action, 118, 121, 262frost heave test, 120frost susceptibility, 118, 119, 120,

262

gabion walls, see wallsgeological origin, 20, 21, 22geometrical data, 245–246, 279, 280,

281, 373, 374gibbsite, 7, 8glacial deposits, 4, 22, 23, 217, 222,

234, 332, 334, 445, 448, 488gleying, 4grading, see particle size distributiongravel, 4, 15, 17, 209, 472

correction for, see oversizeparticles

description, 18, 23 gravity walls, see wallsground freezing, 121, 314ground investigation, 248, 250, 277,

500 et seqcontaminated land, 519–520depth, 502–503extent, 501–502in situ testing, see in situ testingmethods, 503 et seqreports, 243, 244, 500, 520–525

Index 543

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ground investigation (continued)sampling, see sampling

ground model, 246, 250, 253, 349,500, 502, 522

groundwater, see also piezometer;water table

lowering, 83, 171, 176observations, 512, 516 et seq, 521,

523occurrence, 47, 48removal, 176–178

gyttja, 15, 17

halloysite, 8, 9, 10hand augering, see ground

investigation, methodshead, see pressure headings, see ground investigation,

methodsheave, 73, 74, 88, 90, 117, 119, 260,

262, 308, 334, 388, 389heaving, 49, 50, 89, 90horizontal

displacement, 260, 308, 398–399,400–401, 446–447

stress, see stresshumus, 15, 17Hvorslev surface, 226, 229–230

hydraulic consolidation cell, 57,58, 59, 165, 167

hydraulic fracture, 59, 79, 81hydraulic gradient, 51, 52, 54, 55,

56, 65, 69, 72, 73, 74, 87, 278critical, 73, 91, 158

ice lenses, 118, 119, 262illite, 8, 9, 10, 12, 35, 176inclined loading, see bearing

capacityin situ curve, 153, 154in situ testing

dilatometer test, 515–516Dutch cone penetrometer, 513–514field vane test, 514pressuremeter, 514–515, 516SPT, 512–513

index tests, see liquid limit; plasticlimit; shrinkage limit

isochrones, 159, 160isomorphous substitution, 7isotropic soil, 63, 70, 106, 110, 127,

134, 156, 157

Jackfield, UK, case study, 446–448joints, see discontinuities

kaolinite, 8, 9, 10, 12, 35K0 condition, see earth pressure, at

rest

laminated clay, 5, 21, 119, 167, 298layered profiles, 47, 54, 55, 69, 85,

87, 88, 134, 135, 137, 139, 276,278, 310, 330, 399, 401, 428,449, 522, 524

layering, principle of, 291leaching, 5, 102, 235leaning instability, 314levees, see flood banklime stabilisation, 465, 485–486 limit state design, serviceability,

136, 246, 247, 250, 287, 288, 289limit state design, ultimate

base stability, 388, 389boiling, 91characteristic values, see

characteristic valuescorrelation factors, see pilesdesign values, see design valuesfoundations, 263, 264, 279, 280,

281, 282, 287, 304, 309, 310,315, 323

geotechnical, 247heaving, 73, 88, 89, 90, 247internal erosion, 73, 247limit states, 190, 246 et seq, 249,

250, 309 partial factors, see partial factorspiles, see pilespiping, 74quick condition, 72, 73reinforced soil, 390–396sliding, 271–272, 283–284slope stability, see slope stabilityuplift, 71, 72, 91, 92, 93, 247 walls, see walls

walls, surcharge, 373–374line load, 134, 135, 374, 375liquidity index, 9, 13, 31, 32, 35, 44,

234liquid limit, 15, 16, 19, 20, 22, 33,

34, 35, 43, 118, 179, 212, 234,297, 410, 465, 488

local shear failure, 265Lodalen, Norway, case study,

445–446loess, 6, 15Los Vaqueros Dam, California, USA,

case study, 74

M6 Motorway, UK, case study,488–489

made ground, 1, 14, 15, 22, 23, 207,503

median size, 27, 40Mexico City, Mexico, case study,

155, 178–179Mexico City clay, 179middle third rule, 269, 381model factors, 248, 331, 354 modulus

bulk, 194drained, 163, 164, 297, 298, 304,

305, 516effect of strain, 252, 292–293,

299, 300, 321increasing, 134, 291–292, 293,

299, 301, 321, 346shear, 193undrained, 289, 291, 292, 293,

294–295 Young’s, 193

Mohr–Coulomb relationship, 199,266

Mohr’s circle of strain, 194, 195Mohr’s circle of stress, 200, 201,

217, 218, 238, 360, 361, 362moisture condition value, 467,

469–471, 486, 490moisture content, 9, 13, 15, 22, 30,

31, 33, 37, 38, 40, 41, 163, 179,448

moisture sensitivity, 471, 472, 488,489

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monitoring, 244, 277, 309, 312, 313,314, 350, 398–399, 400–401,443, 500, 502, 521

montmorillonite, 8, 9, 10, 12, 35, 277

mudflows, 417, 419

negative skin friction, see piles normally consolidated clay, 98–101,

102, 104, 107, 108, 136, 151,152, 153, 156, 157, 164, 179,219, 220, 221, 223, 225, 227,294, 296, 298, 302, 422, 423

observational method, see Designoedometer

settlement, see settlementtest, 110, 116, 128, 157, 162–164,

206, 302organic soils, see peatoutwash deposits, 4overconsolidated clay, 101, 102, 103,

104, 105, 107, 108, 112, 125,127, 134, 136, 151, 152, 153,154, 164, 181, 219, 220, 221,222, 223, 294, 296, 302, 422,423

overconsolidation ratio, 102, 103,104, 105, 108, 112, 125, 126,152, 181, 214, 229, 230, 294,298, 335, 516

oversize particles, 31, 43, 56, 208,217, 468, 469, 478, 482, 484,488, 494, 495, 496

overturning, 268, 313, 380, 383, 384

packer test, see permeabilitypacking, state of, 12, 13, 208–209partial factors

actions, 252anchors, 251angle of shearing resistance, 252bearing, 252effective cohesion, 252foundations, 279, 280, 281, 282groundwater, 72heave, 88, 89, 90negative skin friction, 342

piles, 251, 329, 330, 331, 340,352, 353, 354, 357

sliding, 252, 283–284slope stability, 425, 426, 427, 428,

430, 432, 434, 435, 438, 441,442, 443, 450, 451, 455, 456

unconfined strength, 252undrained shear strength, 252uplift, 72, 92, 93walls, 385, 386, 402, 403, 404–407walls, surcharge, 373, 374weight density, 252, 428

particledensity, 15, 16, 22, 23, 37, 38, 39,

91, 179effect on strength, 12, 210, 211mineralogy, 6, 209, 218shape, 6, 12, 13, 18, 19, 22, 24,

210size distribution, 13, 16, 17, 18,

22, 24, 25, 26, 27, 28, 40, 52,53, 77, 210, 465

passive pressure, see earth pressurepeat, 3, 6, 14, 15, 17, 18, 23, 29, 31,

34, 83, 295, 298, 303, 473classification, 16, 17description, 16, 17, 22, 23secondary compression, see

secondary compressionperched water table, 48permafrost, 118, 119, 121, 262permeability

borehole tests, 58, 59, 60, 61, 86coefficient, 51, 52, 54–61, 167,

173, 182, 184empirical values, 53, 54laboratory tests, 55, 56, 57, 58, 59,

84layered soils, 54, 55, 85packer test, 61, 62piezometer test, 62, 63, 87, 167pumping test, 63, 64triaxial, 58typical values, 51, 53, 54

personnel, 243PFA, 1, 29, 465, 487phreatic surface, 48, 68, 75, 76, 97,

440

piezocone, 513piezometer, 48, 71

hydraulic, 518–519permeability test, 87pneumatic, 518, 519standpipe, 517–519vibrating wire, 519

piezometrichead, 48, 52level, 48observations, 516, 517

pile groups, block failure, 327, 344, 345efficiency, 343–344, 345individual pile penetration, 344,

345load variation, 334, 343pile cap, 327, 329, 342, 344, 345serviceability limit state, 328, 331,

340, 345, 346, 347, 352settlements, 345, 346, 347, 349spacing, 334, 342, 343, 344, 345,

346stiffness, 342, 343, 349, 352stressed zone, 343, 349

piles, 326 et seqbored, in clay, 332–333, 336, 353,

354bored, in sand, 339, 340critical depth, 337–339, 356 driven, in clay, 332, 333, 334–336,

355driven, in sand, 336–340, 349,

356factor of safety, 340, 341, 346layered deposits, 330, 333, 341limit state design, 326, 327, 328,

340, 341correlation factors, 329, 330,331, 352model factors, 331, 354ultimate capacity, 344, 345, 352

load tests, 327, 328–329, 341, 349,350, 351, 354

negative skin friction, 341–342,356, 357case study, 350–351

types, 326, 327

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piles (continued)ultimate compressive resistance

from static load tests, 329–330,352from ground test results, 330,353, 354from other methods, 330–331

weight of pile, 331piping, 48, 50, 59, 73, 74piston sampler, 510–511plane strain condition, 192, 193, 205,

206, 210plastic limit, 20, 22, 32, 33, 176, 465,

468, 488plasticity

behaviour, 19, 20, 31, 34, 197,198, 200, 277, 471, 472

chart, 20, 34, 35, 44index, 34, 35, 44, 118, 120, 179,

214, 219, 220, 222, 232, 234,259, 260, 297, 301, 465

terms, 20, 35point load, 133, 134, 135, 136, 144,

255, 374, 375Poisson’s ratio, 194, 289, 299, 301,

346pole, 191, 192, 194, 200polluted soils, 2pore pressure, see pressureporosity, 12, 13, 38, 45, 51pozzolana, 485precompression, 171–172, 186preconsolidation pressure, 100, 102,

151, 152, 154, 155, 179, 191,296, 302, 307

pressurechange in pore, 108, 109, 110,

123, 124, 127, 128, 157, 158,159, 184, 204, 237, 298, 334,350, 422, 439, 445, 467

construction, 123, 124, 170, 424,467, 488, 489

head, 51, 62, 67, 70, 71, 87, 88,89, 91, 371, 372

initial pore, 109, 157, 159, 160,161

minimum and maximum, 381,408–412

minimum equivalent fluid, 369parameters, pore, 110, 111, 112,

124, 128, 129, 218, 223, 236,237, 238, 298, 440

pore, 51, 89, 97, 98, 99, 100, 129,158, 159, 216, 223, 371, 372

pore pressure ratio ru, 427, 435uplift, 69, 71, 73, 89pressuremeter test, 514–515, 516

principal stress, see stress, principalpropped walls, see wallspumice, 15pumping test, see permeability

quick clays, 5, 6, 234, 418, 445quick condition, 72, 73

raft foundations, 132, 133, 137, 139,141, 145, 255, 258, 277, 290,315

rapid drawdown, 204, 424reinforced soil, 377

construction, 389–390design, 390–396, 413–414reinforcement, 389, 390

relative deflection, 308relative density, see density indexReports

Geotechnical Design, 243, 244,500, 520

Ground Investigation, 243, 244,520–525

representative values, seecharacteristic values

residual strength, see strengthretaining structures, see wallsrigid foundation, 132, 133, 134,

139ring shear test, 206risk, 244–245, 443, 502

certification, 245register, 245, 500

rocks, weathered, 3, 17Roscoe surface, 226, 228–229rotary drilling, 507–508, 523rotation, 308, 309, 323rotational failure, 419, 429 et seqrunning sand, 49, 83

safety margin, 190, 370, see alsodesign values

samplingblock, 509Delft continuous, 511disturbance, 211, 504, 508groundwater, 512piston, 510–511quality, 508, 509, 521split-barrel SPT, 509, 510,

512–513thin-walled tube, 509, 510U100, 509–510, 523window, 511–512

sandallowable bearing pressure, 272 et

seq, 284, 287bearing capacity, see bearing

capacitydescription, 17, 18, 22, 23, 31, 40drains, 172 frost action, 118, 121normally consolidated, 108, 136,

305, 306, 339overconsolidated, 108, 136, 305,

307, 337, 339parameter Af, 112permeability, 51, 52, 53, 54, 84replacement test, 29, 30settlements, 150, 304 et seqshear strength, see shear strengthstiffness, 132, 133, 136, 207

saprolite, 3saturation

back pressure, 57, 58, 127, 168capillary rise, 99, 112, 113degree of, 37, 45, 112, 164, 493line, see air voids, linespartial, 13, 37, 38, 97, 99, 111,

112, 113, 114, 115, 116, 218process, 223, 236triaxial, 236, 237zone of, 113, 114

Schoharie Creek, USA, case study,277–278

scoria, 15scour, see erosionsecant bored pile walls, see walls

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secondary compression, 103, 154,155, 156, 158, 163, 165, 166,167, 175, 295, 302–304, 305,349, 400

sedimentation test, 25, 26seepage

anisotropic soils, 68, 69deflection rule, 68, 69effect on slope stability, 426, 427,

445flow nets, 66, 67, 68, 69, 70, 74,

371force, 72, 83, 90pressure, 72, 89quantities, 54, 69, 70, 87, 89, 91theory, 63 et seq

selected materials, 464, 465sensitivity, see clayserviceability, see limit state designsettlement, see pilessettlement, consolidation, 287, 295 et

seq, 313, 316compression index, 163, 164, 179,

180, 181, 296–297, 319oedometer, 184, 185, 295,

297–298, 299, 320time, 150, 161, 170, 171, 172,

174, 175, 178, 184, 185, 186,187

settlement, immediate, 287, 288, 289et seq, 317

average, 289, 291, 292, 318depth correction, 289, 291, 318during construction, 171, 289,

298, 299, 301general method, 289modulus estimates, 294–295modulus increasing, 289,

291–292, 301, 318–319principle of layering, 289, 290,

291, 317, 318principle of superposition, 289,

290, 317rigidity correction, 289, 290, 318yielding, 288, 292, 294, 319

settlements, permissible, 307 et seq,315–316

allowable, 272, 304, 307

criteria for movements, 287, 288,309

damage criterion, 272, 309, 310,323, 349

definitions, 307–309routine limits, 309–310

settlements, regional, 176–179, 295,296, 313, 315

settlements, sand, 150, 272, 304 etseq, 314

Burland and Burbridge method,306–307, 322–323

Schmertmann method, 304–306,321–322

settlements, secondary, 295coefficient of, see coefficient of

settlements, total, 287, 298 et seqgeneral method, 302–304elastic drained method, 299, 300,

301, 321individual piles, 340–341modulus, drained, 297, 298, 299,

300, 301, 321pile groups, 345, 346, 347rigidity correction, 299Skempton–Bjerrum method, 298,

320shape factor, 59, 60, 61, 62, 63, 70,

86, 267, 306shear strength, see strengthshear surfaces, 4, 231, 419sheet piling, see also cofferdams,

anchored or propped, 377, 378,382–386

boiling, 91cantilever, 383–386heave, 73, 74, 90piping, 48, 59, 73, 74seepage, 68, 89

shell and auger, see cable percussionboring

shell fragments, 6shrinkage, 259, 260, 261, 307, 473,

474shrinkage limit, 22, 32, 36sieving, see particle, size distributionsilt, 15, 19, 20, 23, 26, 31, 34, 79, 81,

84, 119, 120, 123

site investigation, 499 et seqdesk study, 501, 519, 520, 522ground investigation, see ground

investigationsite inspection, 501, 519, 520, 522

skin friction, 71, 92, 93, 207, 266,272, 330, 336, 338, 339, 364,365, 366, 367, 369, 382, seealso piles; negative skin friction

slickensided surfaces, 5, 22, 277, 476slides, see slope stabilitysliding, 266, 268, 271, 283–284, 382,

403slope stability, see cuttings; earth

dams; embankmentsBishop simplified method,

433–434, 435, 446, 453, 454,457, 458

circular arc, undrained, 429–430critical circle, 430, 434, 445, 452,

453, 454, 455dry slope, 426, 436, 437, 438, 439,

449effective stress, 425, 432 et seq,

445, 446, 449, 450, 453, 454,455

factor of safety, 425, 426, 427,430, 431, 432, 433, 434, 435,438, 440, 441, 442, 446, 449,452, 453, 454

limit state designcase study, Nicolet landslide,418circular arc, 430effective stress, 432, 434, 435,438, 441, 442, 443, 453, 455first-time slides, 420, 445–446mass movement, 417, 418–419method of slices, 430–433, 451natural slopes, 417, 420,445–448non-circular, 440–441overdesign factor, 430, 435,438, 453, 455, 456, 458plane translational slide,425–428, 447–448, 449, 450pore pressure ratio, 427, 435,438

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slope stability (continued)limit state design (continued)

pre-existing slip surfaces, 419,420, 421, 446–448progressive failure, 420rapid drawdown, 427, 439, 440serviceability, 443stability coefficients, 431, 435,437, 438, 453, 456, 457stability number, 431, 432submerged slopes, 427, 439,457, 458tension crack, 428, 429,430–431three-dimensional, 446undrained, 428, 429, 430–432,451, 453vertical cuts, 428, 429, 451water table, 422, 423, 425, 426,436, 437, 438, 439, 445, 447,449wedge method, 441–442

smectite, see montmorillonitesoftening, 332soil

aeolian, 6classification, 14 et seqdescription, 14 et seq, 22, 521, 523extraction method, 315formation, 1–5glacial, see glacial depositsmarine, 3, 5model, 36, 37, 38moisture, 113nailing, 389section, 522, 524stiffness, 132, 134, 136, 293–294,

295, 305, 319, 485strength terms, 20structure, 10, 11, 12, 13tropical, 3

solum, 3specific gravity, see particle densityspecific volume, 38, 156, 225spread foundations, see foundations,

spreadstability coefficients, see slope

stability

stability numberexcavations, 387, 388 slopes, undrained, 431, 432

standard penetration test, 18, 20, 30,206, 207, 272, 273, 274, 284,299, 304, 306, 307, 322, 330,338, 503, 512–513, 523

standpipe, 517standpipe piezometer, 517–519stone, see gravel strain

control, 205, 208, 213, 215, 224effect of, 194, 196, 395normal, 192, 194rate of, 208, 215, 224reinforced soil, 396representation of, 195, 198shear, 192, 193, 194, 205volumetric, 194, 240yield, 196, 198

strengthcritical state, 224 et seq, 196, 197,

198, 208, 210, 211, 239, 240dry, 19effect of drainage, 202, 203, 205,

206effective stress or drained, clay,

211 et seq, 203, 205, 206, 208,215, 216, 222, 223, 224, 369

failure criterion, 196, 199, 200failure mode, 190, 196peak, 179, 196, 197, 198,

208–211, 222, 236, 448residual, 196, 197, 198, 206, 207,

231–232, 420, 446, 448ring shear test, 206, 207, 212sand, 206 et seqshear box test, 206, 207, 208, 212,

236test procedures, 203, 205, 221triaxial, see triaxial testultimate, 196, 197, 236undrained, clay, 20, 21, 202, 206,

207, 208, 211, 212, 213, 214,215, 216, 217, 218, 219, 223,237, 238, 276, 301, 332, 334,335, 344, 369, 372, 428, 429,468, 469, 471, 514

vane, see vane testvariation with depth, 219–221yield, 196

stresseffective, 98, 99, 100, 102, 103,

105, 106, 125, 126, 127, 128effective, above water table, 113,

114, 115, 127, 129history, 98, 101, 102, 151, 152,

155, 156, 206, 221horizontal, 97, 104, 105, 106, 107,

126, 127, 316, 336, 337, 339,360, see also earth pressure

in the ground, 97 et seqpaths, 106, 201, 202, 227, 228,

229, 230, 238, 239principal, 103, 104, 105, 110, 111,

191 et seqshear, 191 et seqtotal, 28, 97, 98, 99, 100, 105,

106, 125, 126stress distribution

bulbs of pressure, 137, 276, 277circle, 133, 136, 169line load, 134, 135Newmark’s method, 137, 139, 145on walls, see earth pressurepoint load, 134, 135, 144principle of superposition, 137,

138, 141, 145, 147rectangle, flexible, 133, 137, 138,

140, 145, 146, 169rectangle, rigid, 133, 139, 141, 147strip load, 136, 137, 138, 140, 144,

169triangular load, 141, 142, 147uniform pressure, 13, 134,

136–142, 144–148, 168, 169,296

structure, 9, 10, 11, 12, 13, 21, 167,168, 213, 235

structure, mass, 21, 203submerged

density, 90, 98, 100, 125, 217, 427slopes, 427, 439, 457, 458

subsidence, 176–179, 295, 307suction, 99, 103, 104, 113, 114, 115,

116, 117, 118, 259, 260, 427

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sump pumping, 48super-elevation, 263surcharging, 171–172, 186surface area, 9swelling, 116, 117, 118, 307, 473swelling index, 163, 164, 219, 296, 297swelling pressure, 116

Tancred Pit Borehole, Yorkshire,case study, 82

temperature, effect of, 15, 30, 33, 52,53, 118, 119, 121, 259, 260,262, 307

tension cracks, 372, 373, 428, 429,451

Teton Dam, USA, case study, 74, 79,80, 81

thixotropy, 102, 155, 179, 235till

ablation, 4lodgement, 4melt-out, 4

tilt, 270, 277, 308, 309, 312, 313,314, 315, 381

time factor, 159, 160, 161, 162, 164,165, 166, 167, 172, 174, 184,185, 186, 187

topsoil, 15, 464, 465, 473Tower of Pisa, Italy, case study,

312–315Transcona Elevator, Canada, case

study, 276–277translational slides, see slope

stabilitytrees, effects of, 115, 116, 117, 260,

261trial pits, 451triaxial apparatus, 58triaxial test, 214 et seq

compression, 127, 202, 205, 206,207, 215

consolidated drained, 206, 212,216, 221, 224, 240

consolidated undrained, 206, 212,221, 222–224, 236, 237, 238

extension, 110, 202, 205, 206multi-stage, 217, 218quick undrained, 206, 215, 216,

217rate of strain, 215, 224saturation, 223, 236, 237

tropical soils, 3

unconfined compression test, 212undisturbed samples, see samplingundrained, see drainage; shear

strengthuniformity coefficient, 27, 28, 40,

210, 465unit weight, see weight density uplift, 50, 70, 71, 91Usk dam, UK, case study, 123

vane test, 206, 211, 212, 213, 214,see also in situ testing

varved clay, 4, 9, 21, 53, 54, 167Venice, Italy, case study, 176–178,

296void ratio, 12, 29, 38, 45, 91, 99,

150, 158, 159, 163, 164, 179,210, 493

constant, 210voids, 50, 51volcanic soil, 14, 15, 16, 33, 179

wallsadhesion, see adhesionanchored or propped, 377,

384–386basement, 376, 377, 378, 379cantilever, 363, 364, 377,

383–384, 412–413cofferdam, see cofferdamscontiguous bored pile walls, 377,

383crib, 377, 379diaphragm, 377, 383embedded, 247, 371, 372, 376,

377, 378, 382 et seq, 386gabion, 377, 379

gravity, 370, 371, 377, 379 et seq,408–410

masonry, 376, 377reinforced soil, see reinforced soilsecant bored pile walls, 377, 378,

383sheet pile, see sheet pilingwall friction, see skin friction

waste materials, see made groundwater table, 48, 47, 49, 60, 81, 82,

100, 103, 113, 114, 116 capillary rise above, 99, 104, 114,

295correction, 274, 284effect on bearing capacity, 263,

271, 274, 280, 284, 313, 314,337

effect on earth pressures, 370, 371,372, 402, 403

effect on slope stability, see slopestability

effective stresses above, 103, 115,125

instruments for, see groundwater,observations

on borehole record, 523on soil section, 524

water-borne soils, 314weathering

chemical, 2, 12, 33, 235clay, 102, 235grades, 2, 3, 22mechanical, 2oxidation, 5

wedge methodactive thrust, 365–366passive thrust, 366–367reinforced soil, 394, 395, 396slope stability, 441–442

weight density, 28, 29, 38, 40, 41, 97Westergaard material, 135wind-blown soils, 6

yield, 196, 197, 198Young’s modulus, 193

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