土木工程毕业设计外文翻译21913766.docx

土木工程毕业设计外文翻译21913766.docx

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土木工程毕业设计外文翻译21913766

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DESIGNANDEXECUTIONOFGROUNDINVESTIGATIONFOREARTHWORKS

PAULQUIGLEY,FGS

IrishGeotechnicalServicesLtd

ABSTRACT

Thedesignandexecutionofgroundinvestigationworksforearthworkprojectsoutlineofgroundinvestigationmethodswhichcanaugment‘traditionalinvestigationmethods’particularlyforglacialtillboulderclaysoilsispresented.Theissueof‘geotechnicalcertification’israisedandrecommendationsoutlinedonitsmeritsforincorporationwithgroundinvestigationsandearthworks.

1.INTRODUCTION

Theinvestigationandre-useevaluationofmanyIrishboulderclaysoilspresentsdifficultiesforboththegeotechnicalengineerandtheroaddesignengineer.Theseglacialtillorboulderclaysoilsaremainlyoflowplasticityandvaryingproportionsofsand,gravel,cobblesandbouldersinaclayorsiltmatrix.Theamountoffinesgovernstheirbehaviourandthesiltcontentmakesitveryweathersusceptible.

Moisturecontentscanbeboulderclayupto20-25%forMidland,South-WestandNorth-Westlightgreyboulderclaydeposits.Theabilityofboulderclaysoilstotake-infreewateriswellestablishedandpoorplanningofearthworksoftenamplifiesthis.

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

Theselectionprocessshouldaimtomaximisetheuseoflocallyavailablesoilsandwithcarefulevaluationitispossibletouseorincorporate‘poorormarginalsoils’withinfillareasandembankments.Fillmaterialneedstobeplacedatamoisturecontentsuchthatitisneithertoowettobestableandtrafficableortoodrytobeproperlycompacted.

HighmoisturecontentlowstrengthboulderclaysoilscanbesuitableforuseasfillinlowistoclassifythesuitabilityofthesoilsinaccordancewithTable6.1fromSeries600oftheNRASpecificationforRoadWorks（SRW）,March2000.Themajorityofcurrentgroundinvestigationsforroadworksincludesacombinationofthefollowingtogivetherequiredgeotechnicaldata:

▪Trialpits

▪Cablepercussionboreholes

▪Dynamicprobing

▪Rotarycoredrilling

In-situtesting（SPT,variableassessingsoilsuitabilityfromdeepcutareas.Cablepercussionboreholesarenormallysunktoadesireddepthor‘refusal’withdisturbedandundisturbedsamplesrecoveredat1.00mintervalsorchangeofstrata.

Inmanyinstances,cablepercussionboringisunabletopenetratethroughverystiff,boreholesshouldbepreventedandlossoffinesiscommon,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.

Asoutlinedpreviously,Irishboulderclaysusuallycompriseasiltorclaymatrix.Lowplasticitysoilswithfinescontentsofaround10to15%oftenpresentthemostdifficulties.BS5930（1999）nowrecognisesthesedifficultiesindescribing‘mixedsoils’–thefinesoilconstituentswhichgoverntheengineeringbehaviournowtakespriorityoverparticlesize.

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

4.ENGINEERINGPERFORMANCETESTINGOFSOILS

Laboratorytestingisverymuchdictatedbytheproposedend-useforthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombinationofthefollowing:

▪Moisturecontent

▪Particlesizegrading

▪PlasticLimit

▪CBR

▪Compaction（relatingtooptimumMC）

▪Remouldedundrainedshearstrength

Anumberofkeyfactorsshouldbeborneinmindwhenschedulinglaboratorytesting:

▪CompactionCBRMCVtestsarecarriedouton<20mmsizematerial.

▪Moisturecontentvaluesshouldrelateto<20mmsizematerialtoprovideavalidcomparison.

▪Porepressuresarenottakenintoaccountduringcompactionandmayvaryconsiderablybetweenlaboratoryandfield.

▪Preparationmethodsforsoiltestingmustbeclearlystipulatedandagreedwiththedesignatedlaboratory.

Greatcaremustbetakenwhendeterminingmoisturecontentofboulderclaysoils.Ideally,themoisturecontentshouldberelatedtotheparticlesizeand,althoughthisisnotalwayspractical.

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

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

Thistypeofinformationisimportanttoboththedesignerandearthworkscontractorasitprovidesanopportunitytounderstandthepropertiesofthesoilswhentestedasoutlinedabove.Itcanalsoillustratetheadvantagesofpre-draininginsomeinstances.Withmixedsoils,faceexcavationmaybenecessarytoacceleratedrainageworks.

CBRtestingofboulderclaysoilsalsoneedscarefulconsideration,mainlywiththepreparationmethodemployed.Designengineersneedtobeawareofthis,asitcanorderofmagnitudedifferenceinresults.Staticcompactionofboulderclaysoilsisadvisedascompactionwiththe2.5or4.5kgrammeroftenleadstoresult.Also,curingofcompactedboulderclaysamplesisimportantasthisallowsexcessporewaterpressurestodissipate.

5.ENGINEERINGCLASSIFICATIONOFSOILS

InaccordancewiththeNRASRW,generalcohesivefilliscategorisedinTable6.1asfollows:

▪2AWetcohesive

▪2BDrycohesive

▪2CStonycohesive

▪2DSiltycohesive

Thematerialpropertiesrequiredforacceptabilityaregivenandthedesignengineerthendeterminestheupperandlowerboundlimitsonthebasisofthelaboratoryclassificationandengineeringperformancetests.IrishboulderclaysoilsarepredominantlyClass2C.

Clause612oftheSRWsetsoutcompactionmethods.Twoproceduresareavailable:

▪MethodCompaction

▪End-ProductCompaction

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

Asplacingandcompactionofthefillprogresses,thein-situTDDcanbecheckedandnon-conformingareasquicklyrecognisedandcorrectiveactiontaken.Thisprocessrequiresthedesignengineertoreviewthefielddensitieswiththelaboratorycompactionplotsandevaluateactualwith‘theoreticaldensities’.

6.SUPPLEMENTARYGROUNDINVESTIGATIONMETHODSFOREARTHWORKS

ThemoretraditionalmethodsandproceduresoutlinedinSection2.Thefollowingareexamplesofmethodswhicharebelievedtoenhancegroundinvestigationworksforroadprojects:

▪Phasingthegroundinvestigationworks,particularlythelaboratorytesting

▪Excavation&samplingindeeptrialpits

▪Largediametertrialsonpotentiallysuitablecutmaterial

6.1PHASING

Phasinggroundinvestigationworksformanylargeprojectsadvocatedformanyyears–thisisparticularlytrueforroadprojectswheresignificantamountsofgeotechnical