Unsaturated Soils: A fundamental interpretation of soil behaviour

304 Pages·2010·5.28 MB·English

by  E. J. Murray and V. Sivakumar

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Unsaturated Soils
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Unsaturated Soils
A fundamental interpretation of
soil behaviour
E.J.Murray
Director
MurrayRixGeotechnical
UK
V.Sivakumar
SeniorLecturer
Queen’sUniversityBelfast
UK
A John Wiley & Sons, Ltd., Publication
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Thiseditionfirstpublished2010
(cid:1)C E.J.Murray
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LibraryofCongressCataloging-in-PublicationData
Murray,E.J.(EdwardJohn),1949-
Unsaturatedsoils:afundamentalinterpretationofsoilbehaviour/E.J.Murray,V.Sivakumar.
p.cm.
Includesbibliographicalreferencesandindex.
ISBN978-1-4443-3212-4(pbk.:alk.paper) 1. Soilmechanics. 2. Zoneofaeration. I. Sivakumar,V.
II. Title.
TA711.M872010
624.1(cid:2)5136–dc22 2010007734
AcataloguerecordforthisbookisavailablefromtheBritishLibrary.
Setin9.5/11.5ptSabonbyAptara(cid:1)R Inc.,NewDelhi,India
PrintedinMalaysia
1 2010
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Contents
Preface viii
Acknowledgements x
Introduction xi
Symbols xiii
1 PropertiesofUnsaturatedSoils 1
1.1 Natureandgenesisofunsaturatedsoils 1
1.2 Soilvariables 3
1.3 Particleproperties 7
1.4 Phasepropertiesandinteractions 9
1.5 Soilstructure 22
1.6 Experimentaltechniquesforexaminingporesizedistribution 23
1.7 Poresizedistribution 25
1.8 Conclusions 32
2 SuctionMeasurementandControl 34
2.1 Introduction 34
2.2 Techniquesformeasurementofsuction 35
2.3 Controlofsuctioninlaboratorytests 52
2.4 Conclusions 56
3 LaboratoryTechniques 57
3.1 Introduction 57
3.2 Materialselectionandspecimenpreparation 58
3.3 Experimentaltechniquesforvolumechangeandstrengthmeasurements 64
3.4 Essentialmeasurements 69
3.5 Furtherdetailsoftriaxialandstresspathtestingtechniques 71
3.6 Conclusions 85
4 BackgroundtotheStresses,Strains,Strength,VolumeChangeand
ModellingofUnsaturatedSoil 87
4.1 Introduction 87
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vi Contents
4.2 Stressesinsoils 88
4.3 Strainsinsoils 90
4.4 Constitutivemodelling 92
4.5 Criticalstateframeworkforsaturatedsoils 98
4.6 TheconstitutiveBarcelonaBasicModelforunsaturatedsoils 107
4.7 Extendedconstitutiveandelasto-plasticcriticalstateframeworksfor
unsaturatedsoils 112
4.8 Concludingremarks 123
5 ThermodynamicsofSoilSystems 127
5.1 Introduction 127
5.2 Outlineofthermodynamicprinciplesandsystems 128
5.3 Introductiontoequilibriumandmeta-stableequilibrium 129
5.4 Variablesofstate 130
5.5 Extensiveandintensivevariables 131
5.6 Thelawsofthermodynamics 131
5.7 Thermodynamicpotentials 135
5.8 Thermodynamicpotentialsinpractice 138
5.9 Conjugatethermodynamicpairings 142
5.10 Influenceofagravitationalfield 144
5.11 Concludingremarks 145
6 EquilibriumAnalysisandAssumptionsinTriaxialTesting 147
6.1 Introduction 147
6.2 Theminimumprinciplesforthepotentials 147
6.3 Isotropicloadingconditions 149
6.4 Anisotropicloadingconditions 152
6.5 Workinputandthethermodynamicpotential 155
6.6 Thethermodynamicpotentialandaxistranslation 156
6.7 Thethermodynamicpotentialandanaggregatedsoilstructure 157
6.8 Conclusions 158
7 EnthalpyandEquilibriumStressConditionsinUnsaturatedSoils 160
7.1 Introduction 160
7.2 Roleofenthalpy 160
7.3 EnthalpyandTerzaghi’seffectivestressforsaturatedsoils 162
7.4 Enthalpyofunsaturatedsoils 163
7.5 Thesignificanceofα 167
7.6 Stressstateinunsaturatedsoils 171
7.7 Alternativeequilibriumanalysis 172
7.8 Graphicalrepresentationofstressstateinunsaturatedsoils 173
7.9 Stressstatevariablesandconjugatevolumetricvariables 174
7.10 Hysteresis,collapseanddiscontinuitiesinsoilbehaviour 176
7.11 Conclusions 179
8 ShearStrengthandCompressionCharacteristicsofUnsaturatedSoils 180
8.1 Introduction 180
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Contents vii
8.2 Shearstrengthandcriticalstatecharacteristicsofunsaturatedsoils 181
8.3 Equivalentstrengthparameters 200
8.4 Compressionandcriticalstatecharacteristicsofunsaturatedkaolin 200
8.5 Modellingofunsaturatedkaolin 206
8.6 Structure,variablesandparameters 208
8.7 Conclusions 210
9 WorkInput,ConjugateVariablesandLoad-DeformationBehaviourof
UnsaturatedSoils 213
9.1 Introduction 213
9.2 Workinputundertriaxialstressconditions 213
9.3 Componentsofthedeviatorstress 218
9.4 Workinputtounsaturatedsoils 218
9.5 Analysisofthemobilisedstressratios 220
9.6 Continuityrelationshipsbetweenstrain-increments 221
9.7 Stressstatevariablesandconjugatevolumetricandstrain-increment
variables 223
9.8 Themeaningandinterpretationofstressesandstrains 224
9.9 Analysisoftriaxialexperimentaldataonkaolin 232
9.10 Conclusions 251
References 254
Index 273
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Preface
Thebookexaminesthemechanicalpropertiesofunsaturatedsoils.Theaimistoprovide
studentsandresearchersingeotechnicalengineeringwithaframeworkforunderstanding
soilbehaviouratafundamentallevelandamodelforinterpretingexperimentaldata,as
wellasprovidingpractitionerswithadeeperappreciationoftheimportantcharacteristics
of unsaturated soils. A notable theme of the book is the interpretation of experimental
strengthandcompressiondatafromstresspathtestsinthetriaxialcell.
The three phases making up an unsaturated soil are the soil particles, water and air;
thephysicalandchemicalpropertiesofwhichvarywidely.Thebehaviourofsoilsisinflu-
enced by many factors but must be compliant with the general laws of thermodynamics
that provide broad principles to which material behaviour must adhere. The theoretical
analyses are based on sound thermodynamic principles and provide a rigorous method-
ology, justified by comparison with test data, to predict and investigate the mechanical
behaviourofunsaturatedsoils. Wehaveendeavouredtokeepthetheoreticalpartofthe
book interesting but thorough, and have drawn on analogous behaviour in physics and
chemistrytoexplainimportantphenomena.
Chapter 1 provides a basic introduction to soil variables, the phases, the phase inter-
actionsandtherelevanceofsoilstructuretosubsequentdiscussions.Particularreference
is made to mercury intrusion porosimetry (MIP) testing in describing the aggregated,
bi-modalstructureofunsaturatedsoils.
Anup-to-datereviewoflaboratorytestingtechniquesispresentedinChapters2and3,
including suctionmeasurementand controltechniquesin laboratorytriaxialcell testing.
The basis of the testing is important if the ideas developed from thermodynamics are to
beproperlyapplied.
Chapter 4 introduces the stress state variables, critical state and theoretical models
in unsaturated soils. This review of current ideas provides a background to subsequent
analyses,whichdifferprincipallyinthedescriptionofunsaturatedsoilsascontrolledby
a dual stress regime with the relative volumes of the phases playing an essential role in
definingthevolumesthroughwhichthestressesact.
Chapters5and6diveintoadetaileddescriptionofthermodynamicprinciplesasapplied
to multiphase materials under equilibrium conditions. In particular, the significance of
the thermodynamic potentials, including enthalpy, is described. It is shown that it is
possible to deal with anisotropic stress conditions as the thermodynamic potentials are
extensivevariables.Thesignificanceoftheminimisationofthethermodynamicpotentials
atequilibriumandthemeaningsofequilibriumandmeta-stableequilibriumareoutlined.