Dredging Engineering-Part 2 soil 疏浚工程 土质篇

Part2DredgingProcess..........................................................................................................1Chapter1BasicConceptsofSoilMechanics........................................................................................11.1SoilClassification...............................................................................................................11.2SoilProperties....................................................................................................................11.2.1PhaseRelationshipsofSoil..........................................................................................................21.2.2Compactionand/orConsistency.......................................................................................................21.2.3Permeability........................................................................................................................21.3ElementarySoilTests............................................................................................................71.3.1PermeabilityTest....................................................................................................................71.3.2MohrCircle..........................................................................................................................81.3.3CaseStudy..........................................................................................................................101.3.4TriaxialShearTest---MohrFailureEnvelop..........................................................................................121.3.5DirectShearTest---Coulomb’sLaw(1776)...........................................................................................131.3.6StandardPenetrationTest--SPT......................................................................................................161.4PassiveandActiveFailure—Rankine’sTheoryofLateralEarthPressure..................................................171.4.1ActiveStressState.................................................................................................................181.4.2PassiveStressState................................................................................................................201.5StressesintheSubsoil.........................................................................................................201.5.1General.............................................................................................................................201.5.2DeterminationofVerticalStresses..................................................................................................221.5.3OverstressedorUnderstressedPoreWaterinaClayLayer............................................................................241.6Consolidation......................................................................................................................25Acknowledgements..........................................................................................................................25Part2DredgingProcessChapter1BasicConceptsofSoilMechanics1.1SoilClassificationTheobjectofsoilclassificationistodividethesoilintogroupssothatallthesoilsinaparticulargrouphavesimilarcharacteristicsbywhichtheymaybeidentified.Inpractice,therearemanydifferentclassificationsareusedbydifferentinstitutions,mostoftheseclassificationsystemsarebasedontheoutcomeoftheparticlesizedistributionanalysesandtheresultsoftheplotsontheplasticitychartofCasagrande.Table1-1istheinternationallymostacceptedstandardizationofparticle-size-ranges.Table1-1Internationallymostacceptedstandardizationofparticle-size-ranges.fine-grainedcoarse-grainedClaySiltsandgravelstoneColloidsfine2~6medium6~20Coarse20~60fine60~200medium200~600coarse600~2mmfine2~6medium6~20coarse20~60cobbles60~200boulders200~μm(micron)mmTable1-2showstheBritishSoilClassificationSystemforEngineeringpurpose(BS5930,1981).Thenameanddescriptivelettersusedinthissystemareexplainedintable1-3.1.2SoilProperties1.2.1PhaseRelationshipsofSoilSoilisamultiphasesystem,containingthreedistinctphases:solid,liquid(water)andgas(air).Inrealitytheporesinbetweenthesolidparticlesarefilledwithwaterand/orgas,figure1-1(a);however,inordertodefinethephaserelationships,anelementofsoilisschematizedinfigure1-1(b).1.2.2Compactionand/orConsistencyFornaturaldepositsofsoilsthecompactionoftheencounteredlayerin-situisanimportantfeature.Thecompactionofanin-situsandlayerdependsonlargelyontheparticlesizedistribution(figure1-2),themodeofsedimentationandthestresshistory.Forclaysthecompactionmoreorlessdependsonthesamefeaturesbutissomewhatmorecomplicatedbecauseforclaystheinteractionbetweenclayparticlesdependsalsoontheelectricalchargesonthesurfaceoftheparticles.Thereforeitiscommonpracticetodistinguishthenotationcompactionforgranularsoils,whichisexpressedintherelativedensityDrandthenotationconsistencyforcohesivesoils,whichisexpressedintheunstrainedshearstrengthCu.Seetable1-4.1.2.3PermeabilityTheperme