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ProposedDesignPhilosophy,Construction,InstallationandMonitoringMethodAsper22.1.7ofSection1.0ofITB11ProposedDesignPhilosophy,Construction,InstallationandMonitoringMethod(asper22.1.7ofsection1.0)1.SourceofborrowspitindicatingthelocationandquantityWehavelicensegivenbyVietnamauthoritytoexploitaquantityof8,400,000m3inNhaBeriverandthelocationisinNhonTrachdistrict,DongNaiprovince.2.PhysicalproprietiesofproposedfillmaterialThesamplingtestofsandproposedtouseiscarriedoutaccordingtoAASHTOM45-89,C144-88(seeTestResultofAnalysesofSandcomponent).Thespecificweightofthesandis2.634,unitweight1.5g/cm3,organiccontent2.87%andmodules2.52.3.Proposedmethodofstatementandmonitoringdevices3.1MethodstatementAccordingtothegeotechnicalreportofthesite,thevoidratioofthesoftsiltyclay(e)is2.377,andthepermeabilitycoefficient(Kv)5.5*10-7cm/s.Ifweadopt“wickdrainsandpre-loading”methodtoreachasoilbearingcapacityof50Kpa,75Kpa,100Kpaunderthesite’sconditions,theconsolidationperiodwouldbefarbeyondtheproposedworkperiod.Forthepurposeofreducingtheconsolidationperiodoffoundationsoilanoverloadshouldbeadded,thoughtheloadingwouldbe7.30mhightofulfillthebearingcapacityof100Kpa.Obviously,thistechniquewouldbearatremendousnumberofloadingandunloading,whichwouldalsomeanahighconstructioncost.Thestabilityofsideslopewouldalsobedifficulttomonitor.BasedonourpreviousexperienceofsoftsoilimprovementofChinacoastalandHiepPhuocPowerPlantinNhaBe,15kmSoutheastofHochiminhCity,thepre-loadingmethodisappropriateonlyforgeneralarea.Inprocessareawesuggesttoadoptedthefollowingmethod(detailsseedrawings“ProposedProcessAreaPlan”and“ProposedProcessAreaZone”inpage6,7):f=50Kpa,vacuumprecompressionmethod;f=75Kpa,vacuumprecompressionandfillingwater(2.0m)onProposedDesignPhilosophy,Construction,InstallationandMonitoringMethodAsper22.1.7ofSection1.0ofITB22membranemethod;f=100Kpa,vacuumprecompressioncompoundwithloadingmethod.Thehydraulicfillingofseasandshouldbeadoptedundertheelevation+2.80,whichisspecifiedinthetenderdocuments.Butbasedonoursiteinvestigationreport,weproposetousesweetwatersandinsteadofseasandforthesefollowingreasons:(1)Finegradeandhighmudcontentoftheseasand;(2)Nolocalfacilitiesavailablesuchashydraulicfillingmudabsorption.Thebackfillmaterial(sweetwatersand)willbedeliveredbybargestothenearestdockandthencarriedbytruckstothesite.3.2MonitoringdevicesAccordingtotherequirementofthetenderdocuments,settlementgaugeshouldbeinstalledat50mx50mgridandbemeasuredbylevelinginstruments.Inaccordancewiththerequirementoftheowner,thestaticpenetrationtestshouldbecarriedoutatthe10specifiedpointsandthepenetrationinstrumentsshouldbeburiedthroughthewholedepthofthecompressiblesoillayers.Thecompactiontestoffillingmaterialsinsiteshouldbecarriedoutwithheavycompactor.4.Designphilosophytoachievetherequirementofthespecificationforsoilimprovement4.1philosophyofvacuumprecompressionmethodThevacuumprecompressionmethodisusedtoconsolidatefoundationsoil.Thismethodconsistsinlayingonthesurfaceoffoundationsoilasandbed,andininstallingadrainagesystemwithwickdrains.Thesandbeddrainlineisburiedandconnectedwithvacuumsystemtoformanairexhaustandadewateringsystem.Asetofairtightsealmembranesislaidonthesurfaceofthesandbedwithitsedgeburiedinsoil.Thus,anegativepressureareawithinsandbedandfoundationsoilcanbeformedfromairexhaustanddewaturingpumps.Thevacuummethodcanreachasoilbearingcapacityof80KPa.Underthevacuumcondition,soilisinthestateofconsolidatingandProposedDesignPhilosophy,Construction,InstallationandMonitoringMethodAsper22.1.7ofSection1.0ofITB33porewaterisdischargedfromsoilunderthepressuredifference.Theconsolidationiscompletedwhenpressureofsoiltobeconsolidatedisreachingthesamepressureofthedrainagesystem.Thephilosophyofvacuumrecompressionmethodisthatunderthepressuredifference(Pa-Pv),soilcanbeconsolidated;PaindicatesatmosphericpressureandPvindicatesairpressureinthesandbedandtheverticaldrains.Inthecalculationofconsolidationofthefoundationsoil,theRENDULIC-TERZAGETheoryandBICOTTheoryofConsolidationcanbeadoptedwhicharethesameofthoseadoptedinloadingrecompressionmethod.Thedropofthegroundwatertablemayalsoacceleratetheconsolidationoffoundationsoilbesidethepressuredifference.Theeffectivestressinthesoilincreasessuccessivelyduringtheperiodofconsolidationofthefoundationsoilwithvacuumrecompressionmethod.Thehorizontaldisplacementofthesoilistowardthecenteroftheconsolidationareafromthebeginningoftheperiodofvacuumrecompression,whichisdifferentfromtheloadingrecompressionmethod.Sothestabilityofthefoundationsoilwillnotbecomeaproblem,andtherequiredvacuumcapacitycanimmediatelybeobtainedandconsequently,theperiodofvacuumrecompressioncanbecurtailed.Detailsisshownindrawings“DesignPhilosophyforVacuumPrecompression“and“FlowDiagramofVacuumPrecompressionMethod”inpage8,9.Regardingtheshortworkperiodofthisproject,thevacuumcompoundwithloadingrecompressionmethodisusedintheprocessareawheretherequiredbearingcapacityofthefoundationsoilis100Kpa.Ithasbeenprovedfromthetheoreticalcalculationandourpreviousexperiencethattheeffectsofvacuumandloadingrecompressionmethodsontheconsol