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1、DESIGNEXECUTIONOFGROUNDINVESTIGATIONFEARTHWKSPAULQUIGLEYFGSIrishGeotechnicalServicesLtdABSTRACTThedesignexecutionofgroundinvestigationwksfearthwkprojectshasbecomeincreasinglyimptantastheavailabilityofsuitabledisposalarea

2、sbecomeslimitedcostsofimptingengineeringfillincrease.Anoutlineofgroundinvestigationmethodswhichcanaugment‘traditionalinvestigationmethods’particularlyfglacialtillboulderclaysoilsispresented.Theissueof‘geotechnicalcertifi

3、cation’israisedrecommendationsoutlinedonitsmeritsfincpationwithgroundinvestigationsearthwks.1.INTRODUCTIONTheinvestigationreuseevaluationofmanyIrishboulderclaysoilspresentsdifficultiesfboththegeotechnicalengineertheroadd

4、esignengineer.Theseglacialtillboulderclaysoilsaremainlyoflowplasticityhaveparticlesizesrangingfromclaytoboulders.Mostofourboulderclaysoilscontainvaryingproptionsofsgravelcobblesbouldersinaclaysiltmatrix.Theamountoffinesg

5、overnstheirbehaviourthesiltcontentmakesitveryweathersusceptible.Moisturecontentscanbehighlyvariablerangingfromaslowas7%fthehardgreyblackDublinboulderclayupto2025%flSouthWestNthWestlightgreyboulderclaydeposits.Theabilityo

6、fboulderclaysoilstotakeinfreewateriswellestablishedpoplanningofearthwksoftenamplifiesthis.Thefinesoilconstituentsaregenerallysensitivetosmallincreasesinmoisturecontentwhichoftenleadtolossinstrengthrenderthesoilsunsuitabl

7、efreuseasengineeringfill.Manyofourboulderclaysoils(especiallythosewithintermediatetypesiltsfinesmatrix)havebeenrejectedattheionstagebutgoodplanningshowsthattheycaninfactfulfilspecificationrequirementsintermsofcompactions

8、trength.Theionprocessshouldaimtomaximisetheuseoflocallyavailablesoilswithcarefulevaluationitispossibletouseincpate‘pomarginalsoils’withinfillareasembankments.Fillmaterialneedstobeplacedatamoisturecontentsuchthatitisneith

9、ertoowettobestabletrafficabletoodrytobeproperlycompacted.Highmoisturecontentlowstrengthboulderclaysoilscanbesuitablefuseasfillinlowheightembankments(i.e.2to2.5m)butnotsuitableftraffickingbyearthwkplantwithoutusingageotex

10、tileseparatgranularfillcappinglayer.Henceitisvitalthattheearthwkscontractfullyunderststhehlingpropertiesofthesoilsasfmanyprojectsthisiseffectivelygovernedbythetrafficabilityofearthmovingequipment.2.TRADITIONALGROUNDINVES

11、TIGATIONMETHODSWherepossibletriaxialcelltestsshouldbecarriedoutoneitherundisturbedsamples(U100’s)goodqualitycesamplestoevaluatethedrainageacteristicsofthesoilsaccurately.Lowplasticityboulderclaysoilsofintermediatepermeab

12、ility(i.e.Kofthederof105to107ms)canoftenbe‘conditioned’bydrainagemeasures.Thisusuallyentailstheinstallationofperimeterdrainssumpsatcutareasbrowpitssoastoreducethemoisturecontent.Hencewithsmallreductioninmoisturecontentdi

13、fficultglacialtillsoilscanbecomesuitableasengineeringfill.4.ENGINEERINGPERFMANCETESTINGOFSOILSLabatytestingisverymuchdictatedbytheproposedendusefthesoils.TheengineeringparameterssetoutinTable6.1pftheNRASRWincludeacombina

14、tionofthefollowing:?Moisturecontent?Particlesizegrading?PlasticLimit?CBR?Compaction(relatingtooptimumMC)?RemouldedundrainedshearstrengthAnumberofkeyfactsshouldbebneinmindwhenschedulinglabatytesting:?CompactionCBRMCVtests

15、arecarriedouton20mmsizematerial.?Moisturecontentvaluesshouldrelateto20mmsizematerialtoprovideavalidcomparison.?Pepressuresarenottakenintoaccountduringcompactionmayvaryconsiderablybetweenlabatyfield.?Preparationmethodsfso

16、iltestingmustbeclearlystipulatedagreedwiththedesignatedlabaty.Greatcaremustbetakenwhendeterminingmoisturecontentofboulderclaysoils.Ideallythemoisturecontentshouldberelatedtotheparticlesizehaveacrespondinggradinganalysisf

17、directcomparisonalthoughthisisnotalwayspractical.InthemajityofcasestheMCVwhenusedwithcompactiondataisconsideredtoofferthebestmethodofestablishing(checking)thesuitabilityacteristicsofaboulderclaysoil.MCVtestingduringtrial

18、pittingisstronglyrecommendedasitprovidesarapidassessmentofthesoilsuitabilitydirectlyafterexcavation.MCVcalibrationcanthenbecarriedoutinthelabatyatvariousmoisturecontentincrements.Sampledisturbancecanoccurduringtransptati

19、ontothelabatythiscanhaveasignificantimpactontheresultantMCV’s.IGSLhasfoundlargediscrepancieswhenperfmingMCV’sinthefieldonlowplasticityboulderclayswiththosecarriedoutlaterinthelabaty(2to7days).Manyoftheafementionedlowplas

20、ticityboulderclaysoilsexhibittimedependantbehaviourwithsignificantlydifferentMCV’srecdedatalaterdate–increasedvaluescanbeduetothedrainageofthematerialfollowingsamplingtransptationstagewhiledilatancymigrationofwaterfromgr

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