地基勘察与施工中英文对照外文翻译文献Word文件下载.docx
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地基勘察与施工中英文对照外文翻译文献Word文件下载.docx
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DESIGNANDEXECUTIONOFGROUNDINVESTIGATIONFOREARTHWORKS
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.ENGINEERINGPERFORMANCETESTINGOFSOILS
Laboratorytestingisverymuchdictatedbytheproposedend-useforthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombinationofthefollowing:
▪Moisturecontent
▪Particlesizegrading
▪PlasticLimit
▪CBR
▪Compaction(relatingtooptimumMC)
▪Remouldedundrainedshearstrength
Anumberofkeyfactorsshouldbeborneinmindwhenschedulinglaboratorytesting:
▪Compaction/CBR/MCVtestsarecarriedouton<
20mmsizematerial.
▪Moisturecontentvaluesshouldrelateto<
20mmsizematerialtoprovideavalidcomparison.
▪Porepressures
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