Dredging EngineeringPart 2 soil 疏浚工程 土质篇.docx

Dredging EngineeringPart 2 soil 疏浚工程 土质篇.docx

《Dredging EngineeringPart 2 soil 疏浚工程 土质篇.docx》由会员分享，可在线阅读，更多相关《Dredging EngineeringPart 2 soil 疏浚工程 土质篇.docx（36页珍藏版）》请在冰豆网上搜索。

DredgingEngineeringPart2soil疏浚工程土质篇

Part2    DredgingProcess..........................................................................................................1

Chapter1BasicConceptsofSoilMechanics........................................................................................1

1.1SoilClassification...............................................................................................................1

1.2SoilProperties....................................................................................................................1

1.2.1PhaseRelationshipsofSoil..........................................................................................................2

1.2.2Compactionand/orConsistency.......................................................................................................2

1.2.3Permeability........................................................................................................................2

1.3 ElementarySoilTests............................................................................................................7

1.3.1PermeabilityTest....................................................................................................................7

1.3.2MohrCircle..........................................................................................................................8

1.3.3CaseStudy..........................................................................................................................10

1.3.4TriaxialShearTest---MohrFailureEnvelop..........................................................................................12

1.3.5DirectShearTest---Coulomb’sLaw（1776）...........................................................................................13

1.3.6StandardPenetrationTest--SPT......................................................................................................16

1.4 PassiveandActiveFailure—Rankine’sTheoryofLateralEarthPressure..................................................17

1.4.1ActiveStressState.................................................................................................................18

1.4.2PassiveStressState................................................................................................................20

1.5 StressesintheSubsoil.........................................................................................................20

1.5.1General.............................................................................................................................20

1.5.2DeterminationofVerticalStresses..................................................................................................22

1.5.3OverstressedorUnderstressedPoreWaterinaClayLayer............................................................................24

1.6Consolidation......................................................................................................................25

Acknowledgements..........................................................................................................................25

Part2    DredgingProcess

Chapter1BasicConceptsofSoilMechanics

1.1SoilClassification

Theobjectofsoilclassificationistodividethesoilintogroupssothatallthesoilsinaparticulargrouphavesimilarcharacteristicsbywhichtheymaybeidentified.Inpractice,therearemanydifferentclassificationsareusedbydifferentinstitutions,mostoftheseclassificationsystemsarebasedontheoutcomeoftheparticlesizedistributionanalysesandtheresultsoftheplotsontheplasticitychartofCasagrande.Table1-1istheinternationallymostacceptedstandardizationofparticle-size-ranges.

Table1-1Internationallymostacceptedstandardizationofparticle-size-ranges.

fine-grained

coarse-grained

Clay

Silt

sand

gravel

stone

Colloids

fine

2~6

medium

6~20

Coarse

20~60

fine

60~200

medium

200~600

coarse

600~2mm

fine

2~6

medium

6~20

coarse

20~60

cobbles

60~200

boulders

200~

μm（micron）

mm

Table1-2showstheBritishSoilClassificationSystemforEngineeringpurpose（BS5930,1981）.Thenameanddescriptivelettersusedinthissystemareexplainedintable1-3.

1.2SoilProperties

1.2.1PhaseRelationshipsofSoil

Soilisamultiphasesystem,containingthreedistinctphases:

solid,liquid（water）andgas（air）.Inrealitytheporesinbetweenthesolidparticlesarefilledwithwaterand/orgas,figure1-1（a）;however,inordertodefinethephaserelationships,anelementofsoilisschematizedinfigure1-1（b）.

1.2.2Compactionand/orConsistency

Fornaturaldepositsofsoilsthecompactionoftheencounteredlayerin-situisanimportantfeature.Thecompactionofanin-situsandlayerdependsonlargelyontheparticlesizedistribution（figure1-2）,themodeofsedimentationandthestresshistory.Forclaysthecompactionmoreorlessdependsonthesamefeaturesbutissomewhatmorecomplicatedbecauseforclaystheinteractionbetweenclayparticlesdependsalsoontheelectricalchargesonthesurfaceoftheparticles.Thereforeitiscommonpracticetodistinguishthenotationcompactionforgranularsoils,whichisexpressedintherelativedensityDrandthenotationconsistencyforcohesivesoils,whichisexpressedintheunstrainedshearstrengthCu.Seetable1-4.

1.2.3Permeability

Thepermeabilityofthesoildeterminestherateofingressofwaterintothesoil,eitherbygravitationalfloworbydiffusion.Sincetheindividualsandparticlesarenotbondedtogetherbyhydratedwaterandsincetheparticlesarerelativelylarge,thereisaneasyaccessofwaterintothepores.Thereforesandhasagoodpermeability（permeabilityvariesbetweenk=10-2mm/sandk=10-4mm/s）.However,claysarealmostimpermeable（permeabilityvariesbetweenk=10-6mm/sandk=10-8mm/s）.Thetwomainreasonsforthisverylowpermeabilityare:

（1）theparticlesareverysmalli.e.ofcolloidalsize;

（2）thewatersurroundingtheclayparticlesispartlyhydratedand/orelectricallybondedtotheparticleandthereforetheflowofwaterenteringtheporesisverydifficult.

Permeabilityisanimportantsoilpropertythatvariesconsiderablyfordifferenttypesofsoils,asshownintable1-5.Relationsbetweensoiltypeandsoilparametersarelistedintable1-6.

Table1-2BritishSoilClassificationSystemforEngineeringPurposes

Table1-3Namesanddescriptivesymbolsforgradingandplasticitycharacteristics,usedintheBritishSoilClassificationSystemforEngineeringpurposes.

Component

Mainterm

Symbol

Qualifying

Symbol

Coarse

Gravel

Sand

G

S

Wellgraded

Poorlygraded

Poorlygraded,uniform

Poorlygapgraded

W

P

Pu

Pg

Fine

Finesoil,fines

Silt（M-soil）

Clay

F

M

C

Lowplasticity

Intermediateplasticity

Highplasticity

Veryhighplasticity

Extremelyhighplasticity

L

I

H

V

E

Organic

Peat

Pt

Organic

O

Fig.1-2Particlesizedistribution

Table1-4

Compactionofgranularsoils

Consistencyofcohesivesoils

classification

Dr

Classification

Cu[kN/m2]

Veryloose

Loose

Mediumdense

Dense

Verydense

0<15

15-35

35-65

65-85

85-100

Verysoft

Soft

Firmormedium

Stiff

Verystifforhard

<20

20-40

40-75

75-150

>150

Table1-5

Table1-6RelationbetweensoiltypeandsoilparameterstoNEN6740.

1.3 ElementarySoilTests

1.3.1PermeabilityTest

Alreadyinthemiddleofthe19thcentury（1850’s）Darcyexperimentallyfoundhisfamouslaw,whenhestudiedtheflowpropertiesofwaterthroughasand-filter-bed.Forhisexperimentsheusedaset-upsimilartothatshowninFig1-3,withwhichhecouldvarythelength（L）ofthesampleandthewaterpressuresatthetopandatthebottom.

Darcyexperimentallyfoundthatthearteofflow（Q）isproportionaltothefallofhead:

Andinverselyproportionaltothelength（L）ofthesample:

SinceQdenotesthetotaldischarge[m3/s]passingthroughthecross-sectionalarea A[m2]ofthesamplecontainer,itwillbeclearthatthespecificrateofthefloworspecificdischarge（q）hasthedimensionofavelocity[m/s]andalsorepresentsthevelocityvofthefreewaterinthetubewherethereisnosand.

Thereal（average）velocitywithwhichthewaterpassestheporechannelsinsidethesandsampleiscalledtheseepagevelocity（Vs）andcanbedefinedbyusingtheprincipleofcontinuity.Thedischargeofwaterpassingthetotalarea（A）abovethesandsampleperunittimemustalsopassthereducedaveragearea （Ap）oftheporechannelsinthesametime:

or

Theconstant（k）usedintheformulaaboveisthecoefficientofpermeabilitywhichhasthedimensionofavelocity[mm/s]andisanimportantsoilpropertywhichvariesconsiderablyfordifferenttypesofsoils,asshowninTable1-5.Itshouldbenotedthatkvaluesstrictlyapplytowater（200C）.Allotherliquidswillhaveothervaluesforthepermeationconstant,dependingontheviscosity.

Fig.1-3Determinationofthecoefficientofpermeability

1.3.2MohrCircle

Inalmostallsoilmechanicsandfoundationengineeringproblems,whereconcentratedloadsareapplied,thehorizontalandverticalstresscomponentswillnotbeprincipalstresses:

i.e.alsoshearstresseswillactonthehorizontalandverticalplanes.

Fig1-4 Determinationofforcesactingonaninclinedplane

Asamatteroffactspeakingofthe“stressstate”inapointofthesubsoilismeaningless,withoutmentioningtheorientationoftheplaneofinterestonwhichtheforcesact.Thereforethecompl