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ResearchontheCriterionofInstabilityoftheHigh-FillSoftRoadbedChun-YuanLiu,Wen-YiGong,Xiao-YingLi,andJin-NaShiHeBeiUniversityofTechnology㧘TianJin㧘300132ABSTRACT:Inonefleetofafreewayconstruction,therightsideoftheroadbedsuddenlytakenplacetosideslipandcollapselargelytowardsoutside,thentheleftsideofitbegantoslipandcollapsetoo.Theslumpingsectionis130m,andthehighestdegreeofcollapseoftheRoadbedslumpis4.3m,boththepavementofconstructionandthelateralreedfieldwellingupfor1.0m,settlementcrackappearsintheculvertaroundthefleet,amongwhichthewidthoflargestcrackis40cm.Thewalloftheculverthavedistorteddeformation.Thecreepingsectionrangesfromthefreeway“K39+720”to“K39+920”,withinwhich“K39+720”—“K39+868”wastreatedbyPlasticDrainageBoardand“K39+868”—“K39+920”wastreatedbyconcretemixedpiles.Notbeforethefifthdaydidthelandslipstopped.ThemaincontentofthispassageistoanalyzethemainfactorsthataffecttheSlopeprogressivefailurecalculatingresult.Inuseofthistheory,two-dimensionalprogressivefailureabouttheslopementionedabovecanbecalculated;andthenontheresultsoftheslopeprogram,thesecurityanalysisontheslopecombinedwithspecificcharacteristicsiscarried.Atlast,designstandardsonsecurityindicatorsofthehigh-fillsoftsoilroadbedaregiven.ENGINEERINGINTRODUCTIONThetotallengthofthemainroadalongthemotorwayis63.673milesandthejointroadis1.309miles.Themainlineusedsixlanesfreewaydesignstandards.Thedesignspeedis120milesperhour,theroadbedwidthis34.5m;thereare5interchangeoverpasses,8separatedoverpasses,6flyovers,1extremelybigbridge,9bigbridges,33middlebridges,30smallbridges,17channels.ThesoilalongtheroadismainlytheforthformationofthenewECQ,anditiscausedbymarinestrata.Theexposedformationincludessuchkindofsoilasclayey,clay,mud-clayey,mud-clay,silt,finesand,andsoon.Knownfromtheinvestigation,theshallowgroundwaterlevelisverylow.Alongthewholelinewhichtheroadcovers,softsoilandweaksoillayerisverycommon.Astherequestofconstructiontimetable,embankmentsinsomesectionsarefilledwithslag,gravelinsteadoffly-ash,lime-soilandsoon.OnNovember18th2007,theroadbedsuddenlybegantoslipfromthestake“K39+720”to“K39+920”.4mmc+243CopyrightASCE2009GeoHunanInternationalConference2009Downloaded14Dec2010to114.255.122.208.RedistributionsubjecttoASCElicenseorcopyright.Visit(swamp),itislow-lyingandhasalittleupsanddowns,thegroundelevationisbetween0.44—2.25m,.Thesketchofcalculatingcrosssectionisshowninfigure1.9.13614.2834.5014.282%3%2%3%1:1.751:1.750-5-10-15-20RoadbedFiller:slagfoundationhandling:illustration:mixedpiles1.eachfigureisscaledbyM.2.proportion:V:1:350;H:1:350Figure1SketchofcalculatingcrosssectionFreeway:K39+900Thespecificgeologyislikethis:AccordingtotheresultsfromGeologicaldrilling,Standardpenetrationtest,CPTexperiment,andinlaboratory,theformationisdividedintosixmajorlayers.Theparametersareintable1below.Table1.SoilparametersNo.soiltypeThickness(m)eLIa1-2(MPa-1)1Mud-clayey3.0-9.50.911-1.1960.67-1.200.39-0.872Clayey1.3-4.00.628-0.7880.75-0.830.37-0.583Mud-clayey1.7-3.61.105-1.2880.72-1.010.634Finesand1.0-5.9——————5Softsoil4.5-4.90.9980.75-0.930.3-0.45NoEs(MPa)c(kPa)ij㨇0σ(MPa)iτ(MPa)13.6-5.03-105.5-785-11020-2524.5-5.213-318.9-32.2140-16035-4033.1-3.512-243.0105-11020-25422.83023.0-35180-2004054.2-6.528-314.8-14.014036GEOTECHNICALSPECIALPUBLICATIONNO.197244CopyrightASCE2009GeoHunanInternationalConference2009Downloaded14Dec2010to114.255.122.208.RedistributionsubjecttoASCElicenseorcopyright.Visit’ssafetyfactorislowest.Iftheoriginaldesignedfillerisnotstable,theactualfillermustbeunstable.Sowepointsoutthismostdangeroussectionbasedontheoriginaldesignedfiller,andthencheckthesafetyfactoroftheactualfiller.ThecheckingprofilesarethesetwoprofilesasK39+900andK39+800fromtheslumpsections.TheprofileofK39+900Theoriginaldesignfillingmaterialwaslime-soilwhiletheactualmaterialwas50cm’gravelcushionand9.16m’slag.Aftertheslump,thefillerwaschangedtofly-ash.Thethicknesscouldbeneglectedwhencalculating.Thegroundwaterlevelis-0.5m;thefoundationhandlingismixedpiles;thepilesarelaidintriangularform;thediameter“d”is0.5m;thehandlingdepth“hv”is8mandlength“l”is64m;thetotallength“lt”ofthepilesis20644m;thehandlingwidth“hw”is62.5m;thehandlingareais4000;thepilespacingis1.2~1.5m;thedistancetheofpilespacingchangesgradually;thecementincorporationwas5%ofreinforcedsoil;thewater-cementratiois0.5.2mAccordingtothegeologicalsurveydata,theactualformationissimplified,herearetheoriginalfoundationpara