土木工程毕业设计外文翻译1111Word文档下载推荐.docx
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土木工程毕业设计外文翻译1111Word文档下载推荐.docx
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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.
Asoutlinedpreviously,Irishboulderclaysusuallycomprisehighlyvariableproportionsofsands,gravelsandcobblesinasiltorclaymatrix.Lowplasticitysoilswithfinescontentsofaround10to15%oftenpresentthemostdifficulties.BS5930(1999)nowrecognisesthesedifficultiesindescribing‘mixedsoils’–thefinesoilconstituentswhichgoverntheengineeringbehaviournowtakespriorityoverparticlesize.
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.
Thistypeofinformationisimportanttoboththedesignerandearthworkscontractorasitprovidesanopportunitytounderstandthepropertiesofthesoilswhentestedasoutlinedabove.Itcanalsoillustratetheadvantagesofpre-draininginsomeinstances.Withmixedsoils,faceexcavationmaybenecessarytoacceleratedrainageworks.
CBRtestingofboulderclaysoilsalsoneedscarefulconsideration,mainlywiththepreparationmethodemployed.Designengineersneedtobeawareofthis,asitcanhaveanorderofmagnitudedifferenceinresults.Staticcompactionofboulderclaysoilsisadvisedascompactionwiththe2.5or4.5kgrammeroftenleadstohighexcessporepressuresbeinggenerated–henceverylowCBRvaluescanresult.Also,curingofcompactedboulderclaysamplesisimportantasthisallowsexcessporewaterpressurestodissipate.
5.ENGINEERINGCLASSIFICATIONOFSOILS
InaccordancewiththeNRASRW,generalcohesivefilliscategorisedinTable6.1asfollows:
▪2AWetcohesive
▪2BDrycohesive
▪2CStonycohesive
▪2DSiltycohesive
Thematerialpropertiesrequiredforacceptabilityaregivenandthedesignengineerthendeterminestheupperandlowerboundlimitsontheb
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