土木工程专业外文翻译

DESIGNANDEXECUTIONOFGROUNDINVESTIGATIONFOREARTHWORKSABSTRACTThedesignandexecutionofgroundinvestigationworksforearthworkprojectshasbecomeincreasinglyimportantastheavailabilityofsuitabledisposalareasbecomeslimitedandcostsofimportingengineeringfillincrease.Anoutlineofgroundinvestigationmethodswhichcanaugment‘traditionalinvestigationmethods’particularlyforglacialtill/boulderclaysoilsispresented.Theissueof‘geotechnicalcertification’israisedandrecommendationsoutlinedonitsmeritsforincorporationwithgroundinvestigationsandearthworks.1.INTRODUCTIONTheinvestigationandre-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.TRADITIONALGROUNDINVESTIGATIONMETHODSForroadprojects,aprincipalaimofthegroundinvestigationistoclassifythesuitabilityofthesoilsinaccordancewithTable6.1fromSeries600oftheNRASpecificationforRoadWorks(SRW),March2000.Themajorityofcurrentgroundinvestigationsforroadworksincludesacombinationofthefollowingtogivetherequiredgeotechnicaldata:TrialpitsCablepercussionboreholesDynamicprobingRotarycoredrillingIn-situtesting(SPT,variableheadpermeabilitytests,geophysicaletc.)LaboratorytestingTheimportanceof‘phasing’thefieldworkoperationscannotbeoverstressed,particularlywhenassessingsoilsuitabilityfromdeepcutareas.Cablepercussionboreholesarenormallysunktoadesireddepthor‘refusal’withdisturbedandundisturbedsamplesrecoveredat1.00mintervalsorchangeofstrata.Inmanyinstances,cablepercussionboringisunabletopenetratethroughverystiff,hardboulderclaysoilsduetocobble,boulderobstructions.Sampledisturbanceinboreholesshouldbepreventedandlossoffinesiscommon,invariablythisleadstoinaccurateclassification.Trialpitsareconsideredmoreappropriateforrecoveringappropriatesizesamplesandforobservingtheproportionofclaststomatrixandsizesofcobbles,boulders.Detailedandaccuratefielddescriptionsarethereforevitalforcutareasandtrialpitsprovideanopportunitytoexaminethesoilsonalargerscalethanboreholes.Trialpitsalsoprovideaninsightontrenchstabilityandtoobservewateringressanditseffects.Asuitablyexperiencedgeotechnicalengineerorengineeringgeologistshouldsupervisethetrialpittingworksandrecoveryofsamples.Thecharacteristicsofthesoilsduringtrialpitexcavationshouldbecloselyobservedasthisprovidesinformationonsoilsensitivity,especiallyifwaterfromgranularzonesmigratesintothefinematrixmaterial.Veryoften,theconditionofsoilonthesidesofanexcavationprovidesamoreaccurateassessmentofitsin-situcondition.3.ENGINEERINGPERFORMANCETESTINGOFSOILSLaboratorytestingisverymuchdictatedbytheproposedend-useforthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombinationofthefollowing:MoisturecontentParticlesizegradingPlasticLimitCBRCompaction(relatingtooptimumMC)RemouldedundrainedshearstrengthAnumberofkeyfactorsshouldbeborneinmindwhenschedulinglaboratorytesting:Compaction/CBR/MCVtestsarecarriedouton20mmsizematerial.Moisturecontentvaluesshouldrelateto20mmsizematerialtoprovideavalidcomparison.Porepressuresarenottakenintoaccountduringcompactionandmayvaryconsiderablybetweenlaboratoryandfield.Preparationmethodsforsoiltestingmustbeclearlystipulatedandagreedwiththedesignatedlaboratory.Greatcaremustbetakenwhendeterminingmoisturecontentofboulderclaysoils.Ideally,themoisturecontentshouldberelatedtotheparticlesizeandhaveacorrespondinggradinganalysisfordirectcomparison,althoughthisisnotalwayspractical.Inthe