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1、BOILINGFAILUREANDRESUMPTIONOFDEEPEXCAVATION12ByH.-L.ChowandC.-Y.Ou,Member,ASCEABSTRACT:Boilingfailurethatresultsfromdrillingforinstallationofanewpneumaticpiezometerinthe®nalgradeofadeepexcavationinTaipei,Taiwan,ispresentedinthiscasestudy.Theextentofthedamageincludestheboilsofamixtureofsoilandwa
2、terenteringthebottomoftheexcavation,heaveofthecenterposts,inclinationofinternallyhorizontalstruts,subsidenceandexcessivelateralinwarddeformationofthediaphragmwall,andsigni®cantgroundsettlement.Thecorrespondingemergencyeffortstominimizethelossareaddressed.Inaddition,thepaperfocusesontworemedials
3、chemestoresumeexcavationfollowingtheincident.Oneisthegroutingmeasureadoptedbythecontractor,andtheotherisadewateringschemeproposedbythewriters.Constructibility,safety,schedule,andcostofthetwoschemesarecompared.Itisdemonstratedthatadewateringschemeshouldbeconsideredwhereapplicabletomitigateagains
4、tsimilarincidentsintheTaipeimetropolitanareainthefuture.INTRODUCTIONsixlayersinthisformation,namely,SungshanVI(theupmostlayer),V,IV,III,II,andI(thelowestlayer,whichisnextMeasurementofground-waterpressureinthevicinityofanChingmeiFormation).Itwasfoundfromthesiteinvestigationexcavationsupportedbya
5、ninternallybraceddiaphragmwallthatSungshanIIIcontainsathinseamofclay.ChingmeiFor-wouldservebothforthedesignpurposepriortocommence-mation,mainlycomposedofgravelmaterials,extendstoamentofconstructionandasaprewateringindicationof®elddepthtoofartobeknown.TypicalsoilpropertiesofSungshanperformanceof
6、construction.Forinstance,determinationofFormationhavebeendiscussedbymanyinvestigators,[e.g.,preconstructionground-waterpressureand¯uctuationscanbeHuangetal.(1987)].Theground-watertableonthesiteisusedforthedesignpurposetodeterminewaterpressurelocatedatEL198m.ThepiezometricheadofChingmeiFor-again
7、stthewall.Inaddition,effectivenessofpredrainingthemationismeasuredatEL188m.Thisshowsthattheground-groundoradversegroundsettlementduetoloweringthewaterwatertableisaffectedduetoexistenceofimpermeablelayerstablearoundanexcavationduri