DESIGNANDEXECUTIONOFGROUNDINVESTIGATIONFOREARTHWORKSPAULQUIGLEY,FGSIrishGeotechnicalServicesLtdABSTRACTThedesignandexecutionofgroundinvestigationworksforearthworkprojectshasbecomeincreasinglyimportantastheavailabilityofsuitabledisposalareasbecomeslimitedandcostsofimportingengineeringfillincrease.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.2to)butnotsuitablefortraffickingbyearthworkplantwithoutusingageotextileseparatorandgranularfillcappinglayer.Hence,itisvitalthattheearthworkscontractorfullyunderstandsthehandlingpropertiesofthesoils,asformanyprojectsthisiseffectivelygovernedbythetrafficabilityofearthmovingequipment.2.TRADITIONALGROUNDINVESTIGATIONMETHODSForroadprojects,aprincipalaimofthegroundinvestigationistoclassifythesuitabilityofthesoilsinaccordancewithTablefromSeries600oftheNRASpecificationforRoadWorks(SRW),March2000.Themajorityofcurrentgroundinvestigationsforroadworksincludesacombinationofthefollowingtogivetherequiredgeotechnicaldata:TrialpitsCablepercussionboreholesDynamicprobingRotarycoredrillingIn-situtesting(SPT,variableheadpermeabilitytests,geophysicaletc.)LaboratorytestingTheimportanceof‘phasing’thefieldworkoperationscannotbeoverstressed,particularlywhenassessingsoilsuitabilityfromdeepcutareas.Cablepercussionboreholesarenormallysunktoadesireddepthor‘refusal’withdisturbedandundisturbedsamplesrecoveredatintervalsorchangeofstrata.Inmanyinstances,cablepercussionboringisunabletopenetratethroughverystiff,hardboulderclaysoilsduetocobble,boulderobstructions.Sampledisturbanceinboreholesshouldbepreventedandlossoffinesiscommon,invariablythisleadstoinaccurateclassification.Trialpitsareconsideredmoreappropriateforrecoveringappropriatesizesamplesandforobservingtheproportionofclaststomatrixandsizesofcobbles,boulders.Detailedandaccuratefielddescriptionsarethereforevitalforcutareasandtrialpitsprovideanopportunitytoexaminethesoilsonalargerscalethanboreholes.Trialpitsalsoprovideaninsightontrenchstabilityandtoobservewateringressanditseffects.Asuitablyexperiencedgeotechnicalengineerorengineeringgeologistshouldsupervisethetrialpittingworksandrecoveryofsamples.Thecharacteristicsofthesoilsduringtrialpitexcavationshouldbecloselyobservedasthisprovidesinformationonsoilsensitivity,especiallyifwaterfromgranularzonesmigratesintothefinematrixmaterial.Veryoften,theconditionofsoilonthesidesofanexcavationprovidesamoreaccurateassessmentofitsin-situcondition.3.SOILCLASSIFICATIONSoildescriptionandclassificationshouldbeundertakeninaccordancewithBS5930(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.Koftheorderof10-5to10-7m4.ENGINEERINGPERFORMANCETESTINGOFSOILSLaboratorytestingisverymuchdictatedbytheproposedend-useforthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombinationofthefollowing:MoisturecontentParticlesizegradingPlasticLimitCBRCompaction(relatingtooptimumMC)RemouldedundrainedshearstrengthAnumberofkeyfactorsshouldbeborneinmindwhenschedulinglaboratorytesting: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.Staticcompactionofboulderclaysoilsisadvisedascompactionwiththe2.5orrammeroftenleadstohighexcessporepressuresbeinggenerated–henceverylowCBRvaluescanresult.Also,curingofcompactedboulderclaysamplesisimportantasthisallowsexcessporewaterpressurestodissipate.5.ENGINEERINGCLASSIFICATIONOFSOILSInaccordancewiththeNRASRW,generalcohesivefilliscategorisedinTable6.1asfollows:2AWetcohesive2BDrycohesive2CStonycohesive2DSiltycohesiveThematerialpropertiesrequiredforacceptabilityaregivenandthedesignengineerthendeterminestheupperandlowerboundlimitsonthebasisofthelaboratoryclassificationandengineeringperformancetests.IrishboulderclaysoilsarepredominantlyClass2C.Clause612oftheSRWsetsoutcompactionmethods.Twoproceduresareavailable:MethodCompactionEnd-ProductCompactionEndproductcompactionisconsideredmorepractical,especiallywhengoodcompactioncontroldatabecomesavailableduringtheearlystagesofanearthworkscontract.AminimumTargetDryDensity(TDD)isconsideredveryusefulforthecontractortoworkwithasameansofcheckingcompactionquality.Oncethematerialhasbeenapprovedandmeetstheacceptabilitylimits,thenin-situdensitycanbemeasured,preferablybynucleargaugeorsandreplacementtestswherethestonecontentislow.Asplacingandcompactionofthefillprogresses,thein-situTDDcanbecheckedandnon-conformingareasquicklyrecognisedandcorrectiveactiontaken.Thisprocessrequiresthedesignengineertoreviewthefielddensitieswiththelaboratorycompactionplotsandevaluateactualwith‘theoreticaldensities’.6.SUPPLEMENTARYGROUNDINVESTIGATIONMETHODSFOREARTHWORKSThemoretraditionalmethodsandprocedureshavebeenoutlinedinSection2.Thefollowingareexamplesofmethodswhicharebelievedtoenhancegroundinvestigationworksforroadprojects:Phasingthegroundinvestigationworks,particularlythelaboratorytestingExcavation&samplingindeeptrialpitsLargediameterhighqualityrotarycoredrillingusingair-mistorpolymergeltechniquesSmall-scalecompactiontrialsonpotentiallysuitablecutmaterialPHASINGPhasinggroundinvestigationworksformanylargeprojectshasbeenadvocatedformanyyears–thisisparticularlytrueforroadprojectswheresignificantamountsofgeotechnicaldatabecomesavailableoverashortperiod.Onthemajorityoflargegroundinvestigationprojectsnoperiodisleftto‘digest’orreviewthepreliminaryfindingsandre-appraisethesuitabilityofthemethods.Withregardtosoillaboratorytesting,largetestingschedulesareoftenpreparedwithnorealconsiderationgiventotheirenduse.Inmanycases,thescheduleispreparedbyajuniorengineerwhiletheseniordesignengineerwhowillprobablydesigntheearthworkswillhavenorealinvolvement.Itishighlightedthattheengineeringperformancetestsareexpensiveandoflongduration(e.g.5pointcompactionwithCBR&MCVateachpointtakesinexcessoftwoweeks).Whenclassificationtests(moisturecontents,particlesizeanalysisandAtterbergLimits)arecompletedthenamoreincisiveevaluationcanbecarriedoutonthedataandtheengineeringperformancetestsscheduled.IfMCV’sareperformedduringtrialpittingthenagoodassessmentofthesoilsuitabilitycanbeimmediatelyobtained.DEEPTRIALPITSTheexcavationofdeeptrialpitsisoftenperceivedascumbersomeanddifficultandthereforenotconsideredappropriatebydesignengineers.Excavationofdeeptrialpitsinboulderclaysoilstodepthsofupto12misfeasibleusingbenchingtechniquesandsumppumpingofgroundwater.Inrecentyears,IGSLhasundertakensuchdeeptrialpitsonseverallargeroadgroundinvestigationprojects.Thedataobtainedfromthesehascertainlyenhancedthegeotechnicaldataandprovidedabetterunderstandingofthebulkpropertiesofthesoils.Itisrecommendedthatthisworkbecarriedoutfollowingcompletionofthecablepercussionboreholesandrotarycoredrillholes.Thegroundwaterregimewithinthecutareawillplayanimportantroleingoverningthefeasibilityofexcavatingdeeptrialpits.Theinstallationofstandpipesandpiezometerswillgreatlyassisttheunderstandingofthegroundwaterconditions,hencethepurposeofundertakingthisworklateoninthegroundinvestigationprogramme.Largerepresentativesamplescanbeobtained(usingtrenchbox)andin-situshearstrengthmeasuredonblocksamples.Thestabilityofthepitsidewallsandgroundwaterconditionscanalsobeestablishedandcomparedwithlevelsinnearbyboreholestandpipesorpiezometers.Overaprominentcutareaofsay500m,threedeeptrialpitscanproveinvaluableandthespoilmaterialalsousedtocarryoutsmall-scalecompactiontrials.Fromavalueengineeringperspective,thecostofexcavatingandreinstatingtheseexcavationscanbeeasilyrecovered.Aprovisionalsumcanbeallocatedinthegroundinvestigationandusedforthiswork.HIGHQUALITYLARGEDIAMETERROTARYCOREDRILLINGThissystementailstheuseoflargediameterrotarycoredrillingtechniquesusingairmistorpolymergelflush.Tripletubecoredrillingiscarriedoutthroughtheoverburdensoilswiththerecoveredmaterialheldinaplasticcoreliner.Corerecoveryinlowplasticityboulderclayhasbeenshowntobeextremelygood(typicallyinexcessof90%).Thehighcorerecoverypermitsdetailedengineeringgeologicalloggingandprovisionofsamplesforlaboratorytesting.Indrumlinareas,suchasthosearoundCavanandMonaghan,IGSLhasfoundtheuseoflargediameterpolymergelrotarycoredrillingtobeverysuccessfulinrecoveringverystiff/hardboulderclaysoilsfordeeproadcutareas(wherecablepercussionboreholesandtrialpitshavefailedtopenetrate).In-situtesting(vanes,SPT’setc)canalsobecarriedoutwithinthedrillholetoestablishstrengthandbearingcapacityofdiscretehorizons.Largediameterrotarydrillingcostsusingtheaforementionedsystemsaretypically50to60%greaterthanconventionalHQcoresize,butagainfromavalueengineeringaspectcanprovemuchmoreworthwhileduetothequalityofgeotechnicalinformationobtained.SMALL-SCALECOMPACTIONTRIALSTheundertakingofsmall-scalecompactiontrialsduringthegroundinvestigationprogrammeisstronglyadvised,particularlywhere‘marginallysuitable’soilsarepresentinprominentcutareas.Inadditiontovalidatingthelaboratorytestdata,theyenablemorerealisticplanningoftheearthworksandcanprovideconsiderablecostsavings.Thecompactiontrialcanprovidethefollowing:Achievablefielddensity,remouldedshearstrengthandCBREstablishingoptimumlayerthicknessandnumberofrollerpassesResponseofsoilduringcompaction(staticvdynamic)Monitortrafficability°reeofrutting.Atypicalsizetestpadwouldbeapproximately20x10minplanareaanduptointhickness.Theselectedareashouldbeclosetothecutareaorborrowpitandhaveadequateroomforstockpilingofmaterial.Earthworkplantwouldnormallyentailatrackedexcavator(CAT320orequivalent),25tdumptruck,D6dozerandeitheratowedorself-propelledroller.In-situdensitymeasurementonthecompactedfillbynucleargaugemethodisrecommendedasthisfacilitatesrapidmeasurementofmoisturecontents,dryandbulkdensities.Italsoenablesalargesuiteofdatatobegeneratedfromthecompactedfillandtoassesstherelationshipbetweendegreeofcompaction,layerthicknessandnumberofrollerpasses.Bothdisturbedandundisturbed(U100)samplesofthecompactedfillcanbetakenforlaboratorytestingandvalidationchecksmadewiththefielddata(particularlymoisturecontents).IGSL’sexperienceisthatwithgoodplanningasmall-scalecompactiontrialtakestwoworkingdaystocomplete.7.SUPERVISIONOFGROUNDINVESTIGATIONPROJECTSCloseinteractionandmutualrespectbetweenthegroundinvestigationcontractorandtheconsultingengineerisconsideredvitaltothesuccessoflargeroadinvestigationprojects.Aseniorgeotechnicalengineerfromeachoftheaforementionedpartiesshouldliasecloselysothatthedirectionandscopeoftheinvestigationcanbechangedtoreflectthestratigraphyandgroundconditionsencountered.Thenatureoflargegroundinvestigationprojectsmeansthattheremustbegoodcommunicationandflexibilityinapproachtoobtainingdata.Bepreparedtocompromiseasmethodsandproceduresspecifiedmaynotbeappropriateandsiteconditionscanquicklychange.Fromasupervisionaspect(bothcontractorandconsultingengineer),theemphasisshouldbeonthequalityofsite-basedgeotechnicalengineers,engineeringgeologistsasopposedtoquantitywhereworkisduplicated.8.GEOTECHNICALCERTIFICATIONTheDepartmentofTransport(UK)preparedadocument(HD22/92)in1992forhighwayschemes.Thissetsouttheproceduresanddocumentationtobeusedduringtheplanningandreportingofgroundinvestigationsandconstructionofearthworks.RoadprojectsinvolvingearthmovingactivitiesorcomplexgeotechnicalfeaturesmustbecertifiedbytheDesignOrganisation(DO)-consultingengineeroragentauthority.TheprofessionalresponsibilityforthegeotechnicalworkrestswiththeDO.Forsuchaproject,theDOmustnominateacharteredengineerwithappropriategeotechnicalengineeringexperience.He/sheisreferredtoastheGeotechnicalLiaisonEngineer(GLE)andisresponsibleforallgeotechnicalmattersincludingpreparationofproceduralstatements,reportsandcertificates.Section1.18ofHD22/92statesthat“oncompletionofthegroundinvestigationworks,theDOshallsubmitareportandcertificatecontainingallthefactualrecordsandtestresultsproducedbythespecialistcontractortogetherwithaninterpretativereportproducedeitherbythespecialistcontractororDO”.TheDOshallthenprepareanEarthworksDesignReport–thisreportistheDesigner’sdetailedreportonhisinterpretationofthesiteinvestigationdataanddesignofearthworks.TheextentandclosenessoftheliaisonbetweentheProjectManagerandtheGLEwillverymuchdependonthenatureoftheschemeandgeotechnicalcomplexitiesdiscoveredastheinvestigationanddesignproceed.Aftertheearthworksarecompleted,ageotechnicalfeedbackreportisrequiredandistobepreparedbytheDO.Thisaddressesthegeotechnicalissuesandproblemsencounteredduringtheconstructionearthworksandcorrectiveactionormeasurestaken.CertificatesarepreparedbytheDOtosignoffonthegeotechnicalmeasurescarriedout(e.g.unstableslopes,karstfeatures,disused/abandonedmineworkings,groundimprovementsystemsemployed,etc).9.CONCLUSIONSCloseco-operationisneededbetweengroundinvestigationcontractorsandconsultingengineerstoensurethatthegeotechnicalinvestigationworkfortheroadsNDPcanbesatisfactorilycarriedout.Manysoilsaretooeasilyrejectedatselection/designstage.Itishopedthattheproposedmethodsoutlinedinthispaperwillassistdesignengineersduringscopingandspecifyingofgroundinvestigationworksforroadprojects.Withmoderninstrumentation,monitoringofearthworksduringconstructionisverystraightforward.Porewaterpressures,lateralandverticalmovementscanbeeasilymeasuredandprovideimportantfeedbackontheperformanceoftheengineeredsoils.Phasingofthegroundinvestigationworks,particularlylaboratorytestingisconsideredvitalsothatthedatacanbeproperlyevaluated.Disposalof‘marginal’soilswillbecomeincreasinglydifficultandmoreexpensiveasthewastelicensingregulationsaretightened.TheadventoflandfilltaxintheUKhasseenthoroughexaminationofallsoilsforuseinearthworks.ThisislikelytoprovideasimilarincentiveandchallengetogeotechnicalandcivilengineersinIrelandinthecomingyears.AcertificationapproachcomparablewiththatoutlinedshouldbeconsideredbytheNRAforgroundinvestigationandearthworkactivities.土方工程的地基勘察與施工保羅·圭格利愛爾蘭巖土工程服務有限公司摘要：當工程場地的處理面積有限且填方工程費用大量增加時，土方工程的地基勘察設計與施工已逐漸地變得重要。由于冰漬土以及含礫粘土的提出使土方工程地基勘察方法的綱要比傳統(tǒng)的勘察方法更詳細。本文提出“巖土認證”觀點以及對地基勘察與土方工程相結(jié)合的優(yōu)點加以概要說明。1、引言許多愛爾蘭含礫粘土的勘察與再利用評價使巖土工程師與道路工程師感到為難。這些冰漬土或含礫粘土主要表現(xiàn)為低可塑性而且還含有從粘土到漂石的不同粒徑顆粒。大部分本地粘土與淤泥質(zhì)土中包含不同比例的砂、礫石、卵石、漂石。顆粒級配控制著土體的行為，而且淤泥使土體性質(zhì)易受天氣變化影響。土體含水量隨著地區(qū)不同而不同，從都柏林硬灰黑含礫粘土的7%到中部、西南部或西北部淺灰色含礫粘土沉積物的20%-25%。含礫粘土吸附水的能力建立的較好但土方工程中計劃的不恰當常導致其擴大。一般來說，良好級配的土體對于含水量的輕微變大相當敏感，將導致強度下降或不適合用作工程回填土。許多含礫粘土（尤其中等淤泥質(zhì)土或良好級配的砂）在選擇階段已經(jīng)被篩除，但事實上它們能對壓縮或強度起到特定的作用。篩選過程應盡量使用本地土體或者回填區(qū)或路堤邊性質(zhì)相對較差的土體，通過仔細評價應加以應用?；靥畈牧媳仨毐３忠欢ǖ暮浚炔荒芴珴駥е峦馏w不穩(wěn)定也不能太干以致不能被充分壓縮。高含水量、低強度含礫粘土適用于低路堤回填（相當于2到的高度）但不適用于沒有使用土工織布隔離與回填層的土方回填工程。因此，土方工程承包商充分認識土體的處理特性相當重要，因為許多工程都受到挖掘設備通行能力的影響。2、傳統(tǒng)地基勘察方法對于道路工程來講，地基勘察最基本目標是對土體適用性進行類似表6.1的分類，該表源于國家檔案登記處2000年3月版的道路施工規(guī)范。目前大部分道路施工中的地基勘察包含以下提供有關(guān)巖土參數(shù)的試驗方法：◆取樣孔◆靜壓法取樣◆動力探測◆回轉(zhuǎn)鉆進◆原位測試（標準貫入試驗，變水頭滲透試驗，巖土物理試驗等）室內(nèi)試驗評價場地工作的重要性特別是評價土體深部取樣區(qū)域的適用性時不能過分強調(diào)其適用性。靜壓法取樣通常將取樣器下沉至要求深度進行取樣，并每間隔一米進行取樣。在許多情況下，靜壓法取樣由于卵石、漂石阻礙不能壓入非常堅硬的含礫粘土。土樣在鉆孔內(nèi)應盡量少擾動，但級配變壞是很正常的，級配變壞將導致土樣分類不夠精確。取樣孔對于恢復適當尺寸的土樣以及觀察碎屑巖在卵石、漂石中所占比例來說應該是適當?shù)?。因此，詳盡且精確的地區(qū)描述取樣區(qū)域以及取樣空來說都相當重要，而且還為它們提供了檢查土體在鉆孔范圍以外性質(zhì)的良機。取樣孔也提供了孔壁穩(wěn)定性的評價以及觀察孔壁內(nèi)水進入時所造成的影響。一位有經(jīng)驗的巖土工程師或工程地質(zhì)專家應監(jiān)督取樣孔工作以及土樣的恢復。因為土樣性質(zhì)為土樣敏感性提供了信息，所以取樣時土體性質(zhì)應被密切關(guān)注，尤其是水從小顆粒區(qū)域遷移到良好級配區(qū)域。而且土體在開挖時的條件為其原位條件提供了一個相對精確的評價。3、土的分類土的描述與分類應該依照英國標準5930（1999）進行并依照英國標準1337（1990）進行測試。土的工程描述應基于按粒徑大小分級并依照良好級配土的可塑性進行補充。對于許多冰漬土或含礫粘土（混合土）的難點在于其描述與工程性質(zhì)測試的評價。關(guān)于以前的地基勘察綱要，愛爾蘭含礫粘土的粘土與淤泥質(zhì)土中常由易變比例的砂、礫石、卵石組成。良好級配且含水量為10%-15%的低可塑性土最難進行描述與分類?，F(xiàn)在英國標準5930（1999）已認識到描述“混合土”所存在的難點——土的良好級配較之顆粒尺寸對于控制著土的工程性質(zhì)更優(yōu)越。一個關(guān)鍵參數(shù)在土分類以及理解過程中經(jīng)常被低估，該參數(shù)就是滲透系數(shù)K。檢查土的顆粒級配將間接說明土的滲透系數(shù)的大小。假如可能，為了準確評價土體的排水特性，三軸單元試驗將采用無擾動原狀土樣或高質(zhì)量土樣進行試驗。低可塑性的中等滲透性含礫粘土(K大約在10-5到10-7米.秒范圍內(nèi))能經(jīng)常通過不同排水條件進行“模擬”4、土工試驗由于室內(nèi)試驗的許多規(guī)定使其被建議用作土的最后試驗。土的工程參數(shù)列于表6.1，該表源于國家檔案登記處2000年3月版的道路施工規(guī)范。其中包含以下內(nèi)容：◆含水量◆顆粒級配◆塑限◆加州承載比◆密實度（最優(yōu)含水量）◆重塑土不排水抗剪強度當進行室內(nèi)試驗時，大量的關(guān)鍵因素應該被考慮?！裘軐嵍?20mm?！艉繙y試試樣應小于20mm以提供真實有效的對比。壓縮時孔隙壓力未加以考慮可能導致室內(nèi)與實際存在相當大的差異。土樣測試的準備方法必須被明確規(guī)定，而且試驗應在指定試驗室進行。進行含礫粘土的含水量測試時必須非常小心謹慎。理想地說，土的含水量應與其粒徑有關(guān)，而且還有相應的級配分析曲線，雖然該曲線不是具有實際應用價值。在大部分情況下，含水量被應用于密實度被認為是提供了關(guān)于建立含礫粘土適用性特征的最好方法。由于含水量能在開挖后快速評價土體的適用性，故強烈建議在取樣孔中對其進行測試。因此，含水量刻度能夠在實驗室內(nèi)不同含水量增量情況下被采用。土樣擾動常發(fā)生在搬運過程中，這將對含水量的結(jié)果產(chǎn)生重大的影響。地質(zhì)科學研究所在進行低可塑性含礫粘土含水量測定時已經(jīng)土樣含水量由于時間的推移（2到7天）存在巨大的差異。許多上述低可塑性含礫粘土表現(xiàn)出與時間相關(guān)的含水量變化特性。其變化值主要由于土樣取樣時的排水條件，土樣運移以及其體積的膨脹與土中水的遷移將導致土樣破壞或者強度下降。以上資料對于設計者以及土方工程承包商來說都很重要，因為進行上述規(guī)定的測試時它提供了設計者以及土方工程承包商理解土體特性的機會。它能說明在某些情況下先進行排水的所存在的優(yōu)點。對于混合土來說，對土方工程進行開挖時加快排水工程非常有必要。含礫粘土的加州承載比測試也需要非常小心謹慎，尤其是開展測試前所采用的準備工作。設計工程師必須意識到這一點，因為準備工作的誤差將導致試驗結(jié)果的明顯不同。經(jīng)驗表明，采用2.5或4公斤的錘進行含礫粘土的靜態(tài)擊實將導致超高的孔隙壓力，因此將導致加州承載比值變低。被擊實含礫粘土的硬化相當重要，因為土的硬化將使孔隙水壓力消散。5、土的工程分類依照英國標準道路施工規(guī)范，一般的粘性填土分類如表6.1如下所示：2A濕粘性填土2B干粘性填土◆2C含石粘性填土2D粉質(zhì)粘性填土首先按可接受性進行提供土樣特性，然后設計工程師在實驗室分類以及工程性質(zhì)測試基礎進行決定土工程分類的上下限。愛爾蘭含礫粘土基本上都屬于2C含石粘性填土。道路施工規(guī)范612條列出了擊實方法。兩種現(xiàn)有的規(guī)程：◆原狀土樣擊實重塑土樣擊實重塑土樣擊實被認為最實用，特別是在土方工程合同初期階段良好的擊實控制數(shù)據(jù)可被利用。檢驗擊實質(zhì)量時，最小干密度對于合同承包商來說是最有用的。一旦土樣被認可或滿足工程分類要求，然后原位密度才能進行測定，當土樣中含石量較低時，通常采用核子測定儀或換砂試驗進行測定。當布置或擊實回填土時，原位干密度能夠得到檢驗，不夠密實的地方能夠被快速識別并進行擊實。該過程要求設計工程師評價擊實試驗區(qū)域的總體密度并估計現(xiàn)場真實的“理論密度”。6、土工地基勘察方法的補充傳統(tǒng)的勘察方法與規(guī)程已在第二部分進行詳細介紹。接下來講述的是有助于道路工程的地基勘察工作方法的幾個例子：◆地基勘察工作分階段進行，特別是室內(nèi)測試開挖&深取樣孔取樣使用噴氣或聚合物膠質(zhì)體技術(shù)的大直徑高質(zhì)量回轉(zhuǎn)鉆進◆對可能適合挖方的土樣進行小范圍擊實試驗對于許多大型工程來說，地基勘察工作應分階段進行已經(jīng)被提倡許多年了；特別室道路工程更應如此。因為道路工程的大量巖土工程方面數(shù)據(jù)可在短期內(nèi)即可使