土木工程毕业设计外文翻译土方工程的地基勘察与施工.docx

土木工程毕业设计外文翻译土方工程的地基勘察与施工.docx

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土木工程毕业设计外文翻译土方工程的地基勘察与施工

DESIGNANDEXECUTIONOFGROUNDINVESTIGATIONFOREARTHWORKS

ABSTRACT

Thedesignandexecutionofgroundinvestigationworksforearthworkprojectshasbecomeincreasinglyimportantastheavailabilityofsuitabledisposalareasbecomeslimitedandcostsofimportingengineeringfillincrease.Anoutlineofgroundinvestigationmethodswhichcanaugment‘traditionalinvestigationmethods’particularlyforglacialtill/boulderclaysoilsispresented.Theissueof‘geotechnicalcertification’israisedandrecommendationsoutlinedonitsmeritsforincorporationwithgroundinvestigationsandearthworks.

1.INTRODUCTION

Theinvestigationandre-useevaluationofmanyIrishboulderclaysoilspresentsdifficultiesforboththegeotechnicalengineerandtheroaddesignengineer.Theseglacialtillorboulderclaysoilsaremainlyoflowplasticityandhaveparticlesizesrangingfromclaytoboulders.Mostofourboulderclaysoilscontainvaryingproportionsofsand,gravel,cobblesandbouldersinaclayorsiltmatrix.Theamountoffinesgovernstheirbehaviourandthesiltcontentmakesitveryweathersusceptible.

Moisturecontentscanbehighlyvariablerangingfromaslowas7%forthehardgreyblackDublinboulderclayupto20-25%forMidland,South-WestandNorth-Westlightgreyboulderclaydeposits.Theabilityofboulderclaysoilstotake-infreewateriswellestablishedandpoorplanningofearthworksoftenamplifiesthis.

Thefinesoilconstituentsaregenerallysensitivetosmallincreasesinmoisturecontentwhichoftenleadtolossinstrengthandrenderthesoilsunsuitableforre-useasengineeringfill.Manyofourboulderclaysoils（especiallythosewithintermediatetypesiltsandfinesandmatrix）havebeenrejectedattheselectionstage,butgoodplanningshowsthattheycaninfactfulfilspecificationrequirementsintermsofcompactionandstrength.

Theselectionprocessshouldaimtomaximisetheuseoflocallyavailablesoilsandwithcarefulevaluationitispossibletouseorincorporate‘poorormarginalsoils’withinfillareasandembankments.Fillmaterialneedstobeplacedatamoisturecontentsuchthatitisneithertoowettobestableandtrafficableortoodrytobeproperlycompacted.

Highmoisturecontent/lowstrengthboulderclaysoilscanbesuitableforuseasfillinlowheightembankments（i.e.2to2.5m）butnotsuitablefortraffickingbyearthworkplantwithoutusingageotextileseparatorandgranularfillcappinglayer.Hence,itisvitalthattheearthworkscontractorfullyunderstandsthehandlingpropertiesofthesoils,asformanyprojectsthisiseffectivelygovernedbythetrafficabilityofearthmovingequipment.

2.TRADITIONALGROUNDINVESTIGATIONMETHODS

Forroadprojects,aprincipalaimofthegroundinvestigationistoclassifythesuitabilityofthesoilsinaccordancewithTable6.1fromSeries600oftheNRASpecificationforRoadWorks（SRW）,March2000.Themajorityofcurrentgroundinvestigationsforroadworksincludesacombinationofthefollowingtogivetherequiredgeotechnicaldata:

▪Trialpits

▪Cablepercussionboreholes

▪Dynamicprobing

▪Rotarycoredrilling

▪In-situtesting（SPT,variableheadpermeabilitytests,geophysicaletc.）

▪Laboratorytesting

Theimportanceof‘phasing’thefieldworkoperationscannotbeoverstressed,particularlywhenassessingsoilsuitabilityfromdeepcutareas.Cablepercussionboreholesarenormallysunktoadesireddepthor‘refusal’withdisturbedandundisturbedsamplesrecoveredat1.00mintervalsorchangeofstrata.

Inmanyinstances,cablepercussionboringisunabletopenetratethroughverystiff,hardboulderclaysoilsduetocobble,boulderobstructions.Sampledisturbanceinboreholesshouldbepreventedandlossoffinesiscommon,invariablythisleadstoinaccurateclassification.

Trialpitsareconsideredmoreappropriateforrecoveringappropriatesizesamplesandforobservingtheproportionofclaststomatrixandsizesofcobbles,boulders.Detailedandaccuratefielddescriptionsarethereforevitalforcutareasandtrialpitsprovideanopportunitytoexaminethesoilsonalargerscalethanboreholes.Trialpitsalsoprovideaninsightontrenchstabilityandtoobservewateringressanditseffects.

Asuitablyexperiencedgeotechnicalengineerorengineeringgeologistshouldsupervisethetrialpittingworksandrecoveryofsamples.Thecharacteristicsofthesoilsduringtrialpitexcavationshouldbecloselyobservedasthisprovidesinformationonsoilsensitivity,especiallyifwaterfromgranularzonesmigratesintothefinematrixmaterial.Veryoften,theconditionofsoilonthesidesofanexcavationprovidesamoreaccurateassessmentofitsin-situcondition.

3.SOILCLASSIFICATION

SoildescriptionandclassificationshouldbeundertakeninaccordancewithBS5930（1999）andtestedinaccordancewithBS1377（1990）.Theengineeringdescriptionofasoilisbasedonitsparticlesizegrading,supplementedbyplasticityforfinesoils.Formanyofourglacialtill,boulderclaysoils（i.e.‘mixedsoils’）difficultiesarisewithdescriptionsandassessingengineeringperformancetests.

Akeyparameter（whichisoftenunderestimated）inclassifyingandunderstandingthesesoilsispermeability（K）.Inspectionoftheparticlesizegradingswillindicatemagnitudeofpermeability.Wherepossible,triaxialcelltestsshouldbecarriedoutoneitherundisturbedsamples（U100’s）orgoodqualitycoresamplestoevaluatethedrainagecharacteristicsofthesoilsaccurately.

Lowplasticityboulderclaysoilsofintermediatepermeability（i.e.Koftheorderof10-5to10-7m/s）canoftenbe‘conditioned’bydrainagemeasures.Thisusuallyentailstheinstallationofperimeterdrainsandsumpsatcutareasorborrowpitssoastoreducethemoisturecontent.Hence,withsmallreductioninmoisturecontent,difficultglacialtillsoilscanbecomesuitableasengineeringfill.

4.ENGINEERINGPERFORMANCETESTINGOFSOILS

Laboratorytestingisverymuchdictatedbytheproposedend-useforthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombinationofthefollowing:

▪Moisturecontent

▪Particlesizegrading

▪PlasticLimit

▪CBR

▪Compaction（relatingtooptimumMC）

▪Remouldedundrainedshearstrength

Anumberofkeyfactorsshouldbeborneinmindwhenschedulinglaboratorytesting:

▪Compaction/CBR/MCVtestsarecarriedouton<20mmsizematerial.

▪Moisturecontentvaluesshouldrelateto<20mmsizematerialtoprovideavalidcomparison.

▪Porepressuresarenottakenintoaccountduringcompactionandmayvaryconsiderablybetweenlaboratoryandfield.

▪Preparationmethodsforsoiltestingmustbeclearlystipulatedandagreedwiththedesignatedlaboratory.

Greatcaremustbetakenwhendeterminingmoisturecontentofboulderclaysoils.Ideally,themoisturecontentshouldberelatedtotheparticlesizeandhaveacorrespondinggradinganalysisfordirectcomparison,althoughthisisnotalwayspractical.

Inthemajorityofcases,theMCVwhenusedwithcompactiondataisconsideredtoofferthebestmethodofestablishing（andchecking）thesuitabilitycharacteristicsofaboulderclaysoil.MCVtestingduringtrialpittingisstronglyrecommendedasitprovidesarapidassessmentofthesoilsuitabilitydirectlyafterexcavation.MCVcalibrationcanthenbecarriedoutinthelaboratoryatvariousmoisturecontentincrements.SampledisturbancecanoccurduringtransportationtothelaboratoryandthiscanhaveasignificantimpactontheresultantMCV’s.

IGSLhasfoundlargediscrepancieswhenperformingMCV’sinthefieldonlowplasticityboulderclayswiththosecarriedoutlaterinthelaboratory（2to7days）.ManyoftheaforementionedlowplasticityboulderclaysoilsexhibittimedependantbehaviourwithsignificantlydifferentMCV’srecordedatalaterdate–increasedvaluescanbeduetothedrainageofthematerialfollowingsampling,transportationandstoragewhiledilatancyandmigrationofwaterfromgranularlensescanleadtodeteriorationandlowervalues.

CBRtestingofboulderclaysoilsalsoneedscarefulconsideration,mainlywiththepreparationmethodemployed.Designengineersneedtobeawareofthis,asitcanhaveanorderofmagnitudedifferenceinresults.Staticcompactionofboulderclaysoilsisadvisedascompactionwiththe2.5or4.5kgrammeroftenleadstohighexcessporepressuresbeinggenerated–henceverylowCBRvaluescanresult.Also,curingofcompactedboulderclaysamplesisimportantasthisallowsexcessporewaterpressurestodissipate.

5.ENGINEERINGCLASSIFICATIONOFSOILS

InaccordancewiththeNRASRW,generalcohesivefilliscategorisedinTable6.1asfollows:

▪2AWetcohesive

▪2BDrycohesive

▪2CStonycohesive

▪2DSiltycohesive

Thematerialpropertiesrequiredforacceptabilityaregivenandthedesignengineerthendeterminestheupperandlowerboundlimitsonthebasisofthelaboratoryclassificationandengineeringperformancetests.IrishboulderclaysoilsarepredominantlyClass2C.

Clause612oftheSRWsetsoutcompactionmethods.Twoproceduresareavailable:

▪MethodCompaction

▪End-ProductCompaction

Endproductcompactionisconsideredmorepractical,especiallywhengoodcompactioncontroldatabecomesavailableduringtheearlystagesofanearthworkscontract.AminimumTargetDryDensity（TDD）isconsideredveryusefulforthecontractortoworkwithasameansofcheckingcompactionquality.Oncethematerialhasbeenapprovedandmeetstheacceptabilitylimits,thenin-situdensitycanbemeasured,preferablybynucleargaugeorsandreplacementtestswherethestonecontentislow.

Asplacingandcompactionofthefillprogresses,thein-s