Expansive soil laboratory test汇总.docx

Expansive soil laboratory test汇总.docx

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Expansivesoillaboratorytest汇总

Chapter3

Laboratorytesting

3.1Introduction

Inthischapter,thelaboratorytestingisdiscussedindetails,whichincludesset-upandpreparationofexperiments,soilusedfortesting,andthetestprocedures.Theresultsoftestsarepresentedanddiscussedaswell.

Swellinginexpansiveclaysisaresultofchangesinthesoilsuctionorwatercontent.Theswellingpressurecanbedefinedasthepressurerequiredre-compressing,thefullyswollensampletoitsoriginalvolume.

Inthisstudy,oedometertestwasusedtomeasuretheswellingpressureofexpansivesoil.ThesoilssamplesusedinthelaboratorytestwerecollectedfromthefieldsateitherGlenroy（asuburb13kmnorthofMelbourne）,orBraybrook（asuburb9kmwestofMelbourne）.

3.2Shrinkswelltest

InAustralia,themethodfordirectlytestingtheswellingpressurepotentialofexpansivesoilsisgiveninAS1289.7.1.1（StandardsAustralia,2003）.Thetestsincludeacoreshrinkagetestandaswellingtest.Shrinkswelltestisasimplemethodtodeterminetheexpansivepotentialofundisturbedorremoldedclaysoil.ThisisalocalmethodthathasbeenusedbyAustraliageotechnicalengineersforover20years.Howeveritisnotknownwidelyaroundinternationalgeotechnicalcommunity.Theindexiscalculatedbytheswellingandshrinkagechangeofaspecimen（Fityusetal.2005）.Theequationisshownbelow.

（3.1）

Where

;

;

.

3.2.1Testprocedure

Theshrink-swelltestingwascarriedoutaccordingtoAS1289.7.1.1（2003）.Theprocedureofshrinkagetestis:

1.Ashrinkagecorehasadiameterwith45mmandalengthof1.5-2m,whichisshavedfromthesoilsample.Themajorstructuremustbeintegrated.

2.Initialdiameter,lengthandmassarerecorded.

3.Eachendofcoreisaddedasmallpinthatishelptomeasurementduringthedryproceeds.

4.Afterpreparation,theshrinkagecoreisair-dried.

5.Diameter,lengthandmassarerecordedregularlyuntilthesamplestopshrink.

6.Thentheshrinkagecoreistakenoven-driedwith105-110OC,andfinaldimensionandmassneedtoberecorded.

Figure3.1:

Coreshrinkagetest

Thetotalshrinkagestrainshiscalculatedbyequation3.5:

（3.2）

Where

;

;

.

Theswellingtestprocedure（AS1289.7.1.1,2003）isasfollows:

1.Asampleisinstalledsteelcuttingringhasdiameter45mmand20mmheightandtheinitialmoisturecontentandmassisrecorded.

2.Agagetomeasurethesampleheightiszeroedunderanominalseatingpressureof5kPa.

3.Thenaloadof25kPaormorepressureisappliedonthesamplefor30minutesandinitialsettlementisrecorded.Thedisplacementisusedtoadjusttheinitialheightofsampleforswellingstrain.

4.Afterre-zeroeddisplacementgage,thesampleisinundatedwithdistilledwaterandregularlyrecordstheswellingincrement.

5.Finalmoisturecontentandmassismeasuredintheendoftest.

Figure3.2:

Apparatususedfortheswellingtest

（3.3）

Where

;

;

.

3.2.2Testresults

Insummary,shrink-swelltestingisimportantindexforsoilclassification.TheresultgivesIss=1.98%/pF.BasedontheTable3.1,thetestingsoilhaslowreactivity.

Table3.1:

Soilclassificationbasedontheshrink-swellindex（Lietal,2014）

Reactivity

Shrink-swellingindex

（%/pF）

Verylowtolow

<2

Medium

2-4

High

4-6

Veryhigh

>6（Li,Cameron&Ren2014）

3.3Atterberglimittest

Asthe2.2.1.1introduced,AtterbergLimitTestisthemostcommontestforuseinpractice.Thislaboratoryexperimenthasthreeteststhatareplasticlimittest,liquidlimittestandlinearshrinkagelimittest.Afterthesethreetests,thekindsofsoilscanbeindicated,suchassiltorclay.ThesetestsschedulesarefollowingtheAustraliaStanderAS1289.Thesamplesoilsunderwentovendryfor3dayswith105oCandmechanicalsievedwith425

mdiameterbeforetheexperiment.ThesoilshowsinFigure3.4.

Figure3.3:

Soilsamplepreparation

3.3.1Plasticlimittest

Plasticlimitisthemoisturecontentatwhichsoilbeginstobeaplasticmaterial.Inplasticlimittest,soilisrolledtothreadsabout3mmindiameterandstarttocrumbleshowninFigure3.5.Sothemoisturecontentisatthislevelcanindicatethekindofsoil（Budhu2007）.AccordingtoAS1289.3.2.1-2001,thesamplesoilwasrolledbyfingersonaglassplatewithrollingratebetween80to90strokesperminutes.Asmalltinwouldbeweightedbeforethetest,collectedthesoilthreadintothetinandusetodeterminethemoisturecontent.

TheplasticlimitwpcanbecalculatedbasedonAS1289.3.2.1:

（3.4）

Where

;

;

.

Figure3.4:

Plasticlimittest

3.3.2Liquidlimittest

Liquidlimitisthemoisturecontentatwhichsoilbeginstobealiquidstatus.AccordingtoAS1289.3.1.2,liquidlimittestusesonepointcasagrandemethod.Basedonthestandard,theminimumdepthofthesoilisintheliquidlimitapparatusabout1cmandthecutbypaletteknifewith10mmdistanceatthecenterofsoil.Twohalvesofsoilcakesonapparatuswillberantogetherby25blows,andthespeedofturningcrankhandleisat2rev/sec.Figure3.6showstheapparatususedforliquidlimittest.

Figure3.5:

Liquidlimittest

ThestandardAS1289.3.1.2givestheliquidlimitwLdeterminationis:

（3.5）

Where

;

;

.

3.3.3Linearshrinkagetest

Linearshrinkagelimittestisasoilstatusthatisfullysaturated.AccordingAS1289.3.4.1,thefullysaturatedsoilwasfilledintheshrinkagemoldandovendry3daysat105oC.

Figure3.6:

Linearshrinkagetest

TheshrinkagelimitLScanbedeterminedbythefollowingequationfromAS1289.3.4.1:

（3.6）

Where

;

.

Insummary,theplasticindexisimportantindexforsoilclassificationinAtterberglimittest.Itcanbedeterminedasthedifferenceoftheliquidlimitandplasticlimit;theresultofGlenroysoilandBraybrooksoilispresentedinTable3.2andTable3.3respectively.BasedontheUnifiedSoilClassificationSystem,theresultsindicatethatGlenroysoilisclay（showedinFigure3.7andFigure3.8）

Table3.2IndexpropertiesofGlenroysoil

Property

Value

LiquidLimit,wL（%）

60.63

PlasticLimit,wp（%）

16.92

PlasticIndex,Ip（%）

47.71

LinearShrinkage,LS（%）

?

Table3.3IndexpropertiesofBraybrooksoil

Property

Value

LiquidLimit,wL（%）

80.75

PlasticLimit,wp（%）

18.02

PlasticIndex,Ip（%）

62.73

LinearShrinkage,LS（%）

22.10

Figure3.7:

PlasticitychartshowingGlenroysoilstudied

Figure3.8PlasticitychartshowingBraybrooksoilstudied

3.4ShearBoxTests

Shearboxtestisamethodtodeterminetheshearstressofasoildirectly.AlinearfunctioncalledMohr-Coulombasshownbelowisarelationaboutshearstressandnormalstress（AS1289.6.2.2）.

（3.7）

Where

;

;

;

.

3.4.1TestProcedure

1.Initialmoisturecontentanddrydensityaredeterminedforeachspecimenbeforethetest.

2.Thespecimenneedstobeconsolidatedintheshearbox.

3.Toturnonthemachinetodothetestandtakereadingbycomputer,whichincludetheshearstress,horizontalmovementandverticalmovement.Thetimetakentoreachfailureiscalculatedfromthefollowingequation:

（3.8）

Where

;

;

4.Themachinestopsandreservesthedirection,whentheshearboxisreachedthelimitoftravelandtheshearboxgobacktotheinitialpositon.

5.Theshearstressversushorizontaldisplacementneedstobeplated.Thepeakshearstressisestablished,whichistheshearstressunderthenormalstress.

6.Finally,graphofshearstressversusnormalstressisplottedbyMicrosoftExcel（AS1289.6.2.2）.

3.4.2TestResults

Figure3.11showedthefirsttestresultswith14kN/m3drydensity.Fourshearboxtestswereconductedat25,50,100and200kPanormalpressureinordertoestablishalinearrelationshipwithshearpressure.Howeverthe100kPapointwasfailed.TherelationshipbetweenshearstressandnormalstresscanbeseeninFigure3.7.Measuringtheangleofthelinearliegivestheinternalfrictionangel’.Thiswasfoundtobe56.06º.Theeffectivecohesionis117.67kPa.

Theequationis

Figure3.9:

Shearboxtestwithsoildensityof14kN/m3

Figure3.12showsthefirsttestresultswith17.4kN/m3drydensity.Threeshearboxtestswereconductedat100,200and400kPanormalpressuresinordertoestablishalinearrelationshipwithshearpressure.Therelationshipbetweenshearstressandnormalstresscanbeseeninfigure3.8.Measuringtheangleofthelinearliegivestheinternalfrictionangel’.Thiswasfoundtobe49.32º.Theeffectivecohesionis71.51kPa.Theequationis

.

Figure3.10:

Shearboxtestwithsoildensityof17.4kN/m3

Figure3.13showsthefirsttestresultswith18kN/m3drydensity.Fourshearboxtestswereconductedat25,50,100and200kPaNormalpressureinordertoestablishalinearrelationshipwithshearpressure.Howeverthe200kPapointwasfailed.Therelationshipbetweenshearstressandnormalstresscanbeseeninfigure3.9.Measuringtheangleofthelinearliegivestheinternalfrictionangel’.Thiswasfoundtobe76.94º.Theeffectivecohesionis292.22kPa.

Theequationis

Figure3.11:

Shearboxtestwithsoildensityof18kN/m3

3.5Soil-WaterCharacteristicCurve

Thesoil-watercharacteristiccurve（SWCC）alsoknownasthesoil-waterretentioncurve（SWRC）isgenerallyusedtopresentthebehaviorofdeformableunsaturatedsoil.Itprovidestheconnectionbetweenthesoilsuctionandtheamountofwaterinthesoilsuchasthedegreesofsaturation.Italsogivestheessentialcharacteristicsofunsaturatedsoil.Lotsofpropertiesofunsaturatedsoilsuchascoefficientofpermeabi