Materials And Building Techniques

1 GeotechnicalEngineering 2 Contents Introduction.................................................................................................................................................................3 BackgroundofStudy...............................................................................................................................................4 SlopeStability.....................................................................................................................................................4 SoilNailing..........................................................................................................................................................5 ProblemStatement..................................................................................................................................................7 Projectobjectives....................................................................................................................................................8 ResearchQuestions.................................................................................................................................................8 SignificanceoftheStudy........................................................................................................................................8 LiteratureReview........................................................................................................................................................9 Introduction...........................................................................................................................................................10 Euro-code7.......................................................................................................................................................12 Conventionalmethod........................................................................................................................................13 BS8006:1995....................................................................................................................................................14 FHWA...............................................................................................................................................................16 Comparison.......................................................................................................................................................17 Summary...............................................................................................................................................................19 Methodology.............................................................................................................................................................24 Introduction...........................................................................................................................................................24 ComponentsofSoilNailWall..............................................................................................................................26 Tendons.............................................................................................................................................................28 PartsoftheConnection.....................................................................................................................................28 Mouldandgrout................................................................................................................................................30 Centralizers........................................................................................................................................................32 MaterialsandComponentsResistanttoCorrosion...........................................................................................32 TheWall'sSurface............................................................................................................................................33 Removalofwastematerials..............................................................................................................................33 Installingandfinishingthenailsandgrout.......................................................................................................34 ResultsandDiscussion..............................................................................................................................................35 References.................................................................................................................................................................45 3 Byrne,R.J.,Cotton,D.,Porterfield,J.,Wolschlag,C.andUeblacker,G.,1996.Manualfordesignandconstruction monitoringofsoilnailwalls......................................................................................................................................45 Lazarte,C.A.,Robinson,H.,Gmez,J.E.,Baxter,A.,Cadden,A.andBerg,R.,2015.Soilnailwallsreference manual(No.FHWA-NHI-14-007)...............................................................................................................................45 Chee-Meng,C.andYean-Chin,T.,2006.Soilnaildesign:AMalaysianperspective.InInternationalConferenceon Slopes(pp.379-400)..................................................................................................................................................45 Lazarte,C.A.,Elias,V.,Sabatini,P.J.andEspinoza,R.D.,2003.GeotechnicalengineeringcircularNo.7-soilnail walls(No.FHWA-IF-03-017).UnitedStates.FederalHighwayAdministration.OfficeofTechnologyApplications. ...................................................................................................................................................................................45 Yuan,J.,Lin,P.,Mei,G.andHu,Y.,2019.Statisticalpredictionofdeformationsofsoilnailwalls.Computersand Geotechnics,115,p.103168......................................................................................................................................45 Su,L.J.,Chan,T.C.,Yin,J.H.,Shiu,Y.K.andChiu,S.L.,2008.Influenceofoverburdenpressureonsoilnailpullout resistanceinacompactedfill.Journalofgeotechnicalandgeoenvironmentalengineering,134(9),pp.1339-1347. ...................................................................................................................................................................................45 Babu,G.S.andSingh,V.P.,2008.Numericalanalysisofperformanceofsoilnailwallsinseismicconditions.ISET JournalofEarthquakeTechnology,45(1-2),pp.31-40..............................................................................................45 Turner,J.P.andJensen,W.G.,2005.Landslidestabilizationusingsoilnailandmechanicallystabilizedearthwalls: casestudy.JournalofGeotechnicalandGeoenvironmentalEngineering,131(2),pp.141-150...............................45 Lee,C.F.,Law,K.T.,Tham,L.G.,Yue,Z.Q.andJunaideen,S.M.,2001.Designofalargesoilboxforstudyingsoil- nailinteractioninloosefill........................................................................................................................................46 Dai,Z.,Zhao,C.,Guo,C.andLin,P.,2021.Systemreliabilityanalysisofsoilnailwallsagainstfacing failures.InternationalJournalofGeomechanics,21(9),p.04021171.......................................................................46 Lin,P.,Liu,J.andYuan,X.X.,2017.Reliabilityanalysisofsoilnailwallsagainstexternalfailuresinlayered ground.JournalofGeotechnicalandGeoenvironmentalEngineering,143(1),p.04016077....................................46 Babu,G.S.andSingh,V.P.,2009.SimulationofsoilnailstructuresusingPLAXIS2D.PlaxisBulletin,25,pp.16-21. ...................................................................................................................................................................................46 Liu,L.,Wu,R.,Congress,S.S.C.,Du,Q.,Cai,G.andLi,Z.,2021.Designoptimizationofthesoilnailwall-retaining pile-anchorcablesupportingsysteminalarge-scaledeepfoundationpit.ActaGeotechnica,pp.1-24.................46 Tokhi,H.,2016.Astudyofnewscrewsoilnail.RMITUniversity,CivilEnvironmentalandChemicalEngineering,, Melbourne.................................................................................................................................................................46 Introduction 4 BackgroundofStudy SlopeStability Athoroughunderstandingofslopesisnecessaryduetothedangerstheyoffertobothstructures andpeopleduetotwodistincttypesofissues: Thisisaproblemifconstructionorexcavationcausessoilstresschangesthatcauseground collapseonpreviouslystableterrain(theso-called"first-timeslide"). Theconstructionorexcavationofanewstructureontopofapreviouslandslide'sshearsurface maycausetheshearsurfacetoshiftagain. Slopestability,likeotherbranchesofsoilmechanics,distinguishesbetweenshort-andlong-term conditions.It'scriticaltoconsidershort-termrequirementswhenaddingmoreweighttothesoil; however,temporaryworksthatreducetheamountofweightonclaysmayalsoberelevant,asthe depressedporepressurescausedbyexcavation,forexample,maynothaveenoughtimetodissipate beforeanotherweightincreaseisapplied.Short-termsituationscallforthel>"=0analysis,whichmakes useoftheundrainedshearstrengthC"asaninputtotheequation.Themobilizedundrainedshear strengthatfailureinfissuredclayswasfoundtobeconsiderablylowerthanthemobilizedundrained shearstrengthestimatedfromsmall-scaletesting,basedonback-analyzedlosses.Themobilized undrainedshearstrengthistypicallyonly45-60%oftheshearstrengthmeasuredonsamplesof40-50 mmdiameterbecausetinypiecesdonotcontainsimilarfissures,aspreviouslymentioned(whichare planesofweakness). Becausetherateatwhichunloading-inducednegativeporepressuresdiminishesisdifficultto track,thereislittledataonhowlongthe=0analysiscanbereliedupon.However,thesoilweakensand expands;asaresult,decreasingtotalstrength.Thepeakeffectivestrengthparametersc'andf>'areused 5 inthelongtermwhenporepressureshavebeenequalized,andthesoilhasnotpreviouslyfailedinany manner.Togetamoreaccurateestimateofslopestability,youmayusetheresidualstrengthparameters (c'and/>')ifthereisapreexistingshearsurfaceonthesite(asaconsequenceofpreviousslope instability).Dependingontheproject'srequirements,thisinformationmaybegleanedthrougheither stressreversalshearboxtestingorringsheartesting.Theremustfirstbeequilibriumporepressures measuredintheslopetocontinuewiththeresearchbasedoneffectivestress.Severalvariablesaffectthis process,includingtheclimate,localgroundwaterconditionsbeforeconstruction,subsurfacegeometry andfeatures,andtheeffectivestressdependencyofsoilpermeability.ruisoftenselectedbasedonprior experiencewithmonitoredandback-analyzedslopesinpracticeintheUnitedKingdom.Thoughshear strengthissupposedtobemobilizedevenlyovertheslipsurfaceinstabilitycalculations,progressive failureisthoughttooccurinreality.Whilestabilityanalysismayprovideagoodindicationofthe stabilityofaslope'ssafetyfactor,it'salsoknownthatstabilityanalysiscanpredictasurfacefailureona differentsurfacethanwhat'sobservedatthefailurelocation. SoilNailing Themethodofsoilnailingisusedtostrengthenthesoilandmakeitmoresolid.Additionally,itis utilizedtoincreasethestabilityofslopes,excavations,retainingwalls,andotherstructures.Soilnailsare oneofthemostcost-effectiveandpracticalmethodsforretainingwallsfromtoptobottom.Their technologicalfeasibility,speed,anddependabilitymakethemexcellentslopeprotectionandearth retentiondevice. Comparedtootherretainingsystems,soilnailstakeuptheleastamountoffloorarea.The activitiesaregenerallylightandquiet,andthereislittledisruptiontotrafficorthelivesofthosewholive inthesurroundingarea.Forcantileverandanchoredretainingwalls,soilnailseliminatetherequirement forafoundationoranystructuralwhalerbeamsatthebottomofthewall,astheydoforsoilnails.Using thesoilnailingtechnique,wemaycutdownontimeittakestocompletethejobandthenumberof 6 materialsused.Theyareveryadaptableandreadilyadjustable,andthepositionofthenailsmaybe changedifanyobstaclesareencountered.Whenitcomestosoilnailing,littleequipmentisutilized. Theycanhandledifferentialsettlementsinmostcases,anddeflectionofsoilnailsiskeptwithin acceptablelimits.Comparedtootherretainingwallsystems,theyaremorecost-effectivesincethey utilizeshotcreteofminimumthicknessratherthanheavystructuralwalls,whicharerequiredinthecase ofotherretainingwallsystems.Themethodofsoilnailwallbuildingissuggestedinsomesituationsand canoffersignificantadvantages,particularlywhennootheralternativeisavailable. excavationshoringforthetimebeing Siteretainingwallsthatarepermanent Stabilizationoftheslope Portalsleadingintotunnels Roadwaywidening Bridgeabutmentsthatarealreadyinplace Portalsleadingintotunnels Existingretainingstructuresarebeingrepairedandreconstructed. Eventhoughasoilbody'sshearingstrengthandtensilestrengthmaybealmostcompletelydisregarded, thereiscertainstructuralintegritythere.Afterplacingsoilnailsofacertainlengthanddensity,thesoil nailandthesoilbodywillcooperate.Itcancompensateforlackofsoilbodystrengthandcreate compositesoil. Thesoilnailisresponsibleforthemajorityofthefunctionsincompositesoil. 1.Theforceofconstraint. 7 Thestiffness,strength,andspatialcombinationformoftheanchorboltinthesoilareallfactorsto consider.Thepurposeofthesoilnailistolimitthedeformationofthesoilbodyandmakecomposite soilbecomeacohesivewhole. 2.Capacityforbearingloads. Thesoilnailandthesoilbodysustaintheexternalloadandgravitationalstressincompositesoil.After thesoilbodyhasreachedaplasticcondition,stressprogressivelytransferstothesoilnail.Becauseofthe highshearingstrengthofthesoilnail,thebearingcapacityofthesoilnailismoreapparent. 3.Stressistransmittedanddiffused. Underthesameloadcondition,thestrainlevelinsoilnailsectionsislowerthanthestrainlevelinthe plainsoilslope,resultinginadelayintheformationanddevelopmentofcrackingzones. 4.Theconstraintforcethatpreventsslopedeformation. Thesteelfabricsprayedconcretepanelissecuredtotheslopewithasoilnail,preventingexcavation unloadingandswellingdeformationwhilesimultaneouslystrengtheningtheconstraintforceonthe boundary. ProblemStatement Becauseofitstechnicalappropriateness,simplicityofinstallation,andlowmaintenance,soilnail isawidelyutilizedslopestabilizationtechnique.Ifappropriateandsystematicdesignprocessesare followed,thisstabilizationtechniquemaybeusedonslopeswithaheightofmorethan25meters.In general,theminimumfactorofsafety(FOS)neededisdeterminedbythelocalauthority'sapprovedrules orcriteria.InMalaysia,thesuggestionsoftheGeotechnicalEngineeringOfficeHongKong(GEOHK) ortheMalaysianPublicWorksDepartmentshallbereferredto(JKR).Becauseournationis progressivelyadoptingEurocodes,someprojectsmayneeddesigncompliancewithEurocodes7and8. 8 (EC7).However,thecreatedEC7isnotdesignedforreinforcedsoildesign.Therearevariationsin partialfactorsusedbyBS8006andEC7(Malaysianannex)fortheslopethathaveavarietyof consequences.Asaresult,theseuncertaintiesmustberecognizedandinvestigatedbeforeasuggestion fortheMalaysiancontextcanbegiven.Asacasestudyforthisproject,numericalmodelingusingSlide2 softwarewillsimulateasoilnailedslope. Projectobjectives Tounderstandthedesignphilosophiesandmethodsforsoilnailedslopedesignbyaconventional method,EC7andBS8006. Toevaluatethesensitivityofnon-fixedpartialfactorstotheanalysesbasedontheconventional designmethod. ToproposeappropriatevaluesofpartialfactorsforsoilnailedslopedesignwithintheMalaysian context. ResearchQuestions HowdifferentarethefinalEC7andBS8006compliantdesignsfromthatoftheconventional method? Howdothepartialfactorsinfluencethesoilnailedslopeanalysisanddesign? WhataretheappropriatedesignparametersintheMalaysiancontext? SignificanceoftheStudy InMalaysia,evaluatingslopestabilityaccordingtoconventionalpracticeisnormalwhenusing limitequilibriumanalysis.Theestimatedvalueofthesafetyfactoraffectstheslope'sstability.The BritishStandard(BS)isnowusedforglobalsafetyfactors,whiletheEuropeanCommunity(EC7) utilizespartialsafetyfactors.TheBritishStandard'sanalysisisbasedonbothglobalandregional 9 standardinformation.Additionally,thisstudywillexplainhowtotalstressandeffectivestressanalysis relatetothenotionofthesafetyfactor.We'llknowthesoil'sporewaterpressureafterthestudyis complete.Totalstressanalysismayberequirediftheporewaterpressurecannotbedeterminedorisnot known.Short-termstabilityissuesarefrequentlyassessedusingtotalstress.Whendealingwiththis scenario,soilundrainedshearstrengthistakenintoaccountfortheoverallstressanalysisandisconstant withdepth.Theeffectivestresscanonlybecalculatedindirectlywhentheporewaterpressuresare known.Itisessentialinthewaterbusinesstopredictwaterpressureforbothshort-termandlong-term circumstances.Thissituationlendsitselftoananalysisbasedondepletedstrengthparameters. LiteratureReview 10 Introduction Itisnotalwayspossibletouseotherretainingsystemslikereinforcedconcretewallsor reinforcedsoilwallsondistressedslopesornew,verysteepcutslopesbecausesoilnailingoffersthe distinctadvantageofstrengtheningtheslopewithoutrequiringextensiveearthworkstoprovide constructionaccessandworkingspace.Soilmassesaredesignedtoperformbetterin-situbyinserting relativelysmall,thin,bonded,andunstressedsteelbarsintothesoil(alsoknownassoilnailing).This kindofinstallationnecessitatestheuseofsimpleinstallationequipmentsuchasdrillingrigs,grouting machines,andcompressors.Toensureadequatedrainage,thesoilnailsshouldbesetwitha5to10 degreeslopetothehorizontal.Installingitdoesn'ttakeupalotofspace.Theoriginalslopeprofilescan bemaintainedsinceextensivetreeremovalmaybeavoided.Thisindicatesthattheslopehasbeen subjectedtojustthetiniestdegreeofdisturbance.Hydroseedingtheslopesurfacehasthebenefitof beingmoreenvironmentallyfriendlythanconcretespraying.Soilnailshavealowconstructioncost,and sincetheyneedlittlemaintenanceandinspectiononcetheyareinstalled,theyalsohavealow maintenancecost.Whenplanningslopestabilizationoperations,theunderlyinggeologicalprofilesand soilpropertiesthatmaybegleanedthroughstudyandtestinginthelabareusuallytakenintoaccount. Thelength,size,andamountofsoilnailsusedontheslopewilllikelybeinfluencedbyeachofthese factors.Asidefromthat,theappropriatestabilityanalysismethodandsafetyfactorshouldbecarefully chosenastheywillaffectthedesignofthesoilnailonaslope.Priortoplanninganysubsurface explorationoperations,itisnecessarytoconductsurfaceresearchasthefirststageintheinquiryprocess. Deskresearchandfieldreconnaissancearetwowaystolookatsurfacefeatures.Themostfrequentkind ofsurfacefeatureassessmentisadeskstudy.Deskstudiesincludethestudyofmapsandplansto determinesurfacegeologicalcharacteristics,drainagepatterns,andmaterialsexistingonthesite,aswell asaerialphotographsandconstructionrecordsofnearbystructures.Thestudyofspecificdevelopment papersishighlysuggested,astheymayincludeinformationonthesite'sresearch,welldigging,piling, foundation,andpreviousinstabilityofslopes.Thetopographyandnaturaldrainageofthesiteshouldbe 11 examinedwhiledoingfieldreconnaissanceinordertodeterminetheprobableunderlyingstructureofthe site.It'spossibletoobserveevidenceofpreviousslopefailures,aswellassignsofpain.Constructionof manytrialpits,drill-and-boreholes,andotherinquiryholesorpitsisrequiredtogathersoilandrock coresamplesforexamination.Certainon-sitetestsarerequiredtodeterminethedepthofthe groundwatertableandthedensity,shearstrength,andpermeabilityofthesoil.Someexamplesofthese testsareStandardPenetrationTests(SPTs),VaneShearTests,GCOProbeTests,andPressuredWater Tests.Whenthereisasuspicionofmovement,itmaybenecessarytoinstallequipmentforlong-term monitoringofthegroundwatertable,porewaterpressure,ordisplacement.Examplesofthiskindof instrumentincludethestandpipe,peizometer,inclinometer,andtensiometer.Inlaboratorysoiltesting, soilsamplesshouldbecollectedthatareasrepresentativeaspossibleofthematerialsfoundonthework siteinordertobeutilizedinthefield.It'spossibletocarryoutclassificationtestingandshearstrength testinginalabenvironment.Toevaluatethemoisturecontent,voidratio,liquidandplasticlimit,and permeabilityofasoil,classificationtestsarecarriedoutonthesoilsample.Predictionsregardingthe physicalbehaviorofthesoillayersarethenmadebasedontheresultsandconfirmed.Shearstrength testsshouldbecarriedoutinatriaxialcompressionmachineoradirectshearboxundercircumstances thatarecomparabletothosethatthesoilwouldexperienceinthefieldofapplication.Laboratorystudies arerequiredtodeterminethesoil'scohesiveness,frictionalangle,compression,andrecompression indices.Theelementofsafetyisevaluatedbasedonthesite'slocationandtheimplicationsofacollapsed slopetohumanlifeandproperty.For"threattolife"and"economicrisk,"theGeoguidepublishedbythe GeotechnicalEngineeringOfficescategorizesslopesintothreecategories:"negligent,""low,"and "high."Takingintoconsiderationtheworstpossiblegroundwaterconditionsandrainstormsduringan estimated10-yearperiod,thebareminimumsafetyfactoris1,accordingtothechartbelow.Reducethe dangerbyusingalowerfactorofsafetyonslopesnearunderdevelopedterritory.Thisnon-circular failurepatternisthemostcommoninMalaysia.It'sinfluencedbytheamountofweatheringand infiltrationontheslopesthemselves.Thereareseveralnoncircularanalyticalmethodsthatmaybeused 12 ontheseslopes,suchasJanbuandMorgenstern'sorPrice.Thehydro-geologicalpropertiesoftheslope maybedeterminedviaandsubsurfaceinvestigations.Thedesignsoilparametersmaybederivedthrough in-situfieldtestingandlaboratorysoiltesting.Peizometricdatamayalsobeusedtoestimatealocation's groundwatertabledepth.Tobeclear,poresuction'sinfluenceshouldnotbeconstruedasimproving slopestabilitysinceinfiltrationwouldcausesignificantharmtoaslopeifthiseffectweretakeninto consideration.Internationalstandardsofpracticeanddesignguidelinesareavailableforsoilnaildesign, includingthoselistedbelow. Euro-code7 Partialsafetyfactorsmusttakeintoaccountanyadversedeviationsfromthecharacteristicvalue ofthepropertyaswellasanyuncertaintiesinthemodelusedforcalculation,asspecifiedbyEn1990. Basedonthreeconsequencecategories,theramificationsoftheultimatelimitstatesarealsotakeninto account.Toaccountfortherepercussionsoffailure,addasecondcomponenttothevariablesforactions dependingontheoutcomesofthoseactivities.Theoretically,therearetwowaystofigureoutthe differentpartsofsafety.Traditionalapproaches,forexample,usepriorexperiencetocalibratethe variables.Statisticalmethodsandprobabilistictechniquesmayalsocalibratethevariablesagainsta desireddependabilityindexvalue.Itisrecommendedthata50-yearreliabilityindexbe3.8forthe reliabilityclassRC2,whichcorrespondstothemostcommondesignsituations.Inthisscenario,the theoreticalprobabilityofreachingtheultimatelimitstateisabout1/15000.Theauthorsthinkthat materialandresistancefactorsforgeotechnicaldesignhavebeenacquiredmostlyviacalibrationto earliercodes,evenifcertainpartialfactorsforactionshavebeencomputedusingprobabilisticmethods. Itmeansthatwhileestablishingsafetymeasures,bothmaterialqualities(suchasstrength)andactivities shouldbetakenintoaccount(Byrne.,etal,1996).Foraneffectivestressanalysis,partialsoilstrength factorsof1.25arerecommended,whileatotalsoilstrengthfactorof1.4isrecommended.Toconductan 13 effectivestressanalysis,partialfactorsonsoilstrengthshouldhavec'=1.25,whereasfullfactorsshould havec'=1.25.Thetotalsafetyfactortechniquehastraditionallybeenusedtoassessslopestabilitywhile doingstabilityanalyses.Manyengineersthinkthatconnectingtoasinglesafetyfactoriseasysincethere isalotofdataonoverallsafetyfactorsbasedonexperience.Increasedsettlementsarecausedbyan increaseinhorizontalsoilmovements. Thisreductioninoverallsafetyleadstoanincreaseinsettlements(1990).Acomprehensive safetyplanformaintainingslopestabilitymaybeimprovedwiththeuseofempiricalevidence.The inclusionofpartialsafetycomponentsintheEurocodesimpliesthatsafetyisplacedwhereuncertainty existswhilealsoconsideringtheconsequencesoffailure.Accordingtothestudy'sobjectives,wewantto findouthowtruethisassumptionisintermsofslopestabilityandwhatmaybedonetoimproveitinthe future.ThismaybedonebyapplyingpartialresistanceMfactorstotheequation.Consequently,the alternativemethod'smaterial,partialfactors,willbecalculatedforvarioustargetreliabilityindexvalues correspondingtovariousreliabilityclasses. Conventionalmethod Whencreatingstableslopes,severalimportantfactorsneedtobetakenintomind.Soil characteristicsandgeologiccontextsdeterminevirtuallyallslopedesignissues.Inotherwords,notwo slopedesignissuesarethesame.Asecondreasonisthatstabilityestimationtechniquesforexcavation slopesandslopesofembankmentsareidentical.Thustheymaybeutilizedinterchangeably.Tobeclear, thefirsttwocriteriaapplytobothnewlyconstructedandexistingslopesandcorrectivesolutiondesign forbothtypes.Third,buildingastablesloperequiresfieldresearch,laboratorytesting,stability evaluations,andappropriateslopeconstruction.Thebestavailabledatacollectingandanalysismethods mustbecoupledwithsoundengineeringjudgment,experience,andintuitionifasafeandcost-effective slopestabilizationsystemisachieved.Becausethevastmajorityofthework'sspecificscannotbe 14 standardized,excellentengineeringjudgment,experience,andintuitionmustbeusedwiththefinestdata gatheringandanalysismethodsavailable. Thestabilityofaslopehastraditionallybeenconsideredasafetyfactor,butinterestin developingaprobabilisticassessmentofslopereliabilityhasgrownrecently,especiallyinthe constructionsector.Traditiondictatesthatifasafetyfactorislessthanone,itindicatesfailure,oratleast thepotentialoffailure,whereasagreatersafetyfactorindicatesstability.Whencalculatingaslope's safetyfactor,therearemanythingstokeepinmind.Thereareseveralfactorstotakeintoaccountwhen evaluatingdata,suchasthequalityofthesubsurfaceinvestigations,laboratoryandfieldtesting,data interpretation,thequalityofconstructioncontrol,thecompletenessofthedesignprobleminformation(if any),andhowwellthedesignproblemhasbeenaddressed.Inaddition,theengineermustthinkabout theramificationsofafailingsystem.Slopedesignswithsafetyfactorsrangingfrom1.25to1.50are requiredinthemajorityoftransitsituations.Whereaslopemovementcancausehumandeathor significanteconomicloss,orsignificantuncertaintyregardingrelevantdesignparameters,construction qualitycontrol,seismicactivitypotential,etc.,higherfactorvaluesmayberequiredtoprotectagainst suchrisks.Ifanengineerisconfidentintheintegrityoftheinputdataandcanrelyongoodconstruction controlthroughoutthebuildingprocess,lowersafetyfactorsmaybeused. BS8006:1995 BS8006testsincludethestabilityofthefacetopreventerosionandthetransferofloadinthe activezone,bothofwhicharenecessaryforsafeoperation.Tobeclear,whileitincludessuggestionson soilnaildesigninBS8006,itlacksthethoroughnessanduser-friendlinessofthedesigntechniquesgiven inHA68/94andtheFHWAmanual. 15 TheBS8006designapproachmakesuseofthelimitstatenotiononceagain(British Standard).Thelimitequilibriumtechniqueisusedtoevaluatethestabilityofthestructureby testingitsinternalandexternalstabilitiesagainstthelimitstates.HA68includespartialsafety concernsintoitsdesigncalculationtocomplywiththerequirements.Amorecomprehensive explanationofthedifferenttechniquesandassumptionsavailabletothedesignerisprovidedin BS8006insteadofHA68.Eachofthesecomponentfactorsisconnectedtoacertainbuilding conditionorscenario,anditisalsogiven.Inadditiontothelogspiralapproachandthetwo-part wedgetechniquethereareothermethodstousewhentryingtolocatethecriticalfailurepoint.The BritishStandard8006advisesthatiftheshearresistanceissignificant,usersincludeitintotheir designwiththewell-knowntensilereinforcementprovidedbythenails.BS8006definesthe stagesthatadesignershouldconsiderwhenconstructingsoilnailingstructuresintheUnited Kingdom(UK).Thisishowthephasesgo: Tokeeptheactivezonestable,youmustfirstdeterminewherethecriticalslipsurfaceis locatedandhowmuchresistiveforceormomentisneeded. Thereshouldbeacheckateverystage,consideringthevariousstagesofdevelopment,to guaranteethatnothinggoeswrongthroughoutthebuildingprocess. forexample,howmuchstrainisinthenailjustbelowtheslipsurface Removethewholeresistivezonenaillength-wise Bendingandshearingmaybeseenwherethenailmeetstheslipsurface. Assoonasthenailishammeredintotheearth,itcollapses. Animprovednailpatternanddispositionmaybeselectedafterfurtheranalysisbythe designer,whomaythenputitintopractice(Chee-MengandYean-Chin,2006).Anewmethodfor figuringouttheshearloadsinnailswascreatedusingthetheoryofnaildeflectionsand 16 kinematicalcompatibility,bothofwhichwerebasedonlaterallyloadedthinpiles.Thisstandard givesdesignersgreaterleewaywhenselectingtheoptimaldesignstrategyforvarioussituations thandoesHACCP(HazardAnalysisandCriticalControlPoint)(HACP).Thedesigner'sprior experienceandknowledgemustbeconsideredwhenselectingappropriatetechniquesfora suitabledesignbasedonguidancefromthedesignhandbook. FHWA Whenitcomestosoilnailing,theFederalHighwayAdministration(FHWA)utilizesthe limitedequilibriumapproach.Themanualusestheslipsurfacelimitingequilibriumapproachfor soilnailing,particularlyusedbyallcurrentpracticalsoilnailingdesignmethods.Forthesecond timeinthissetofdesignprinciples,thestrengthlimitstate(sometimesreferredtoastheultimate limitstate)andtheservicelimitstateareconsidered.Theseverelimitstate,asubsetofthe strengthlimitstate,identifiesbuildingsthathavebeenexposedtosignificantstressessuchas earthquakesasanotherlimitcondition.IntroducingtheSLDandLRFDtechniquesofdesign,both ofwhichtakeintoconsiderationbothlimitstatesintheircalculations:theSLDandtheLRFD,the handbookintroducestheServiceLoadDesignAsloadsareapplied,recommendedfactorsof safetyareappliedtothesoilstrengthandallowednailloadsareproposedforreinforcingstrength (tendonstrengthandpulloutresistanceofthenail).Theserecommendationsaremadeatbothlimit states.Remembertoaccountforeverytypeoffailuremodewhencalculatingyoursystem's maximumstrength. Thenailreinforcesthesethreeeffects.Foranailtocontributetostructuralstability,itmust haveoneofthreeproperties:alowtensilestrength,highpulloutresistancealongitsentirelength aboveandbeyondaslipsurface,andlowpulloutresistancecombinedwithhighnailheadstrength betweentheheadandaslipsurface.Thisinformationiscarriedoverfromthepreviousparagraphs. 17 Asopposedtodiscretecomponents,thedesignofsoilnailsandwallfacingsisapproachedas asingleintegratedsoil-nail-wall"system."Bydoingthis,wewanttoensurethatthedesignwill holdupovertime.Thisguideonlylooksatthetensilestrengthandignoresthenail'sshearand bendingcontributions.Duetotheirmobilizationoccurringonlyaftersignificantstructural distortion,theothercontributionsaren'tconsidered.Thisassumptionisconservative,accordingto themanual. Designcalculationscanonlybecompletedafterthedesignerhaschosenthewalllayoutand dimensions,aswellasgroundandsubsurfacematerialproperties,todetermineapreliminarynail pattern,whichincludesthelengths,spacing,strengths,andinclinationsofthenailsaswellasthe groundandsubsurfacematerialproperties(Chee-MengandYean-Chin,2006).Thisisalldonewhile consideringthesurroundingenvironment.Nailshammeredintopredrilledholesshouldbeangledata 15-degreeangle,tobeginwith.Groutingwouldbeparticularlydifficultonslopessmallerthan5 degrees;therefore,theseshouldbeavoided.Thenailspacings,lengths,andsizesmustbeallconsistent. Comparison Thelimitedequilibriumanalysisisusedbyallapproaches,andpartialsafetyfactorsareevidentinsome ofthem.Anyissuesregardingtheassumptionofsimultaneousmobilizationofresistancesmustbe addressedwhendoingtheregionalequilibriumanalysis.Additionalempiricaldata(suchasnailspulled outinanailpullouttest)wouldbeusefulforreferenceinthesemanuals(forexample).Forexample,soil nailingmanualsstatethatthemostcommonfailuremechanismsincludetensilefailures,pullouts, bendingandshearingfailures,bearingfailures,instabilityduringexcavation,andoverallslippingofthe reinforcedsoilmass.Thesefailuremechanismsareallfoundinsoilnailingmanuals.Ontheotherhand, theFederalHighwayAdministrationonlylooksatthetensilestrengthandignoresthenail'sshearand bendingcontributions.Accordingtothemanual,thisassumptioniscautioussincetheremaining contributionsarenotuseduntilasignificantamountofdeformationhasoccurred.FollowingClouterre's 18 recommendations,thelimitequilibriummethodshouldbeevaluatedaftertheconstructionprocessandat eachstage.TheFederalHighwayAdministrationacknowledgesbuildingsexposedtohighpressures, suchasseismicloading,andincludesanextremelimitstateasasubsetofthestrengthlimitstate.The FHWAmanualaddressesanadditionaleffectnotcoveredinotherdesignguides:thenailhead attachmenttotheface.Inconjunctionwiththelimitedequilibriumanalysis,furtherinvestigationinto estimatingthenumberofdisplacementsontheproposedsoilnailingstructure. Slopestability,likeotherbranchesofsoilmechanics,distinguishesbetweenshort-andlong-term conditions.It'scriticaltoconsidershort-termrequirementswhenaddingmoreweighttothesoil; however,temporaryworksthatreducetheamountofweightonclaysmayalsoberelevant,asthe depressedporepressurescausedbyexcavation,forexample,maynothaveenoughtimetodissipate beforeanotherweightincreaseisapplied.Short-termsituationscallforthel>"=0analysis,whichmakes useoftheundrainedshearstrengthC"asaninputtotheequation.Themobilizedundrainedshear strengthatfailureinfissuredclayswasfoundtobeconsiderablylowerthanthemobilizedundrained shearstrengthestimatedfromsmall-scaletesting,basedonback-analyzedlosses.Themobilized undrainedshearstrengthistypicallyonly45-60%oftheshearstrengthmeasuredonsamplesof40-50 mmdiameterbecausetinypiecesdonotcontainsimilarfissures,aspreviouslymentioned(whichare planesofweakness). Becausetherateatwhichunloading-inducednegativeporepressuresdiminishesisdifficultto track,thereislittledataonhowlongthe=0analysiscanbereliedupon.However,thesoilweakensand expands;asaresult,decreasingtotalstrength.Thepeakeffectivestrengthparametersc'andf>'areused inthelongtermwhenporepressureshavebeenequalized,andthesoilhasnotpreviouslyfailedinany manner.Togetamoreaccurateestimateofslopestability,youmayusetheresidualstrengthparameters (c'and/>')ifthereisapreexistingshearsurfaceonthesite(asaconsequenceofpreviousslope instability).Dependingontheproject'srequirements,thisinformationmaybegleanedthrougheither 19 stressreversalshearboxtestingorringsheartesting.Theremustfirstbeequilibriumporepressures measuredintheslopetocontinuewiththeresearchbasedoneffectivestress.Severalvariablesaffectthis process,includingtheclimate,localgroundwaterconditionsbeforeconstruction,subsurfacegeometry andfeatures,andtheeffectivestressdependencyofsoilpermeability.ruisoftenselectedbasedonprior experiencewithmonitoredandback-analyzedslopesinpracticeintheUnitedKingdom.Thoughshear strengthissupposedtobemobilizedevenlyovertheslipsurfaceinstabilitycalculations,progressive failureisthoughttooccurinreality.Whilestabilityanalysismayprovideagoodindicationofthe stabilityofaslope'ssafetyfactor,it'salsoknownthatstabilityanalysiscanpredictasurfacefailureona differentsurfacethanwhat'sobservedatthefailurelocation. Summary Thishandbook'smethods,whicharethoroughandrigorousbutalsoeasilyadaptabletoMalaysian practice,serveasabasisforthemostrecommendeddesignprocedures.TheymustsatisfyBS8006 requirements,andcertaingoodpracticesfromHA68/94areincludedtomakethedesignmethodsmore applicabletoMalaysianpractice(Lazarte.,etal,2003).Thedesignprocesswasbrokendownintothe followingstages: DesigningCriticallyIntheprocedure,thefirsttwostagesarecalledcross-sectionsandtrialdesigns, respectively.Choosingatrialdesignsuitableforthedesigngeometryandloadingconditionsbeing evaluatedispartofthisstep.Calculationoffinalsoilstrengthparametersanddesignwatertable locationforvarioussubsurfacelayersisalsorequired(belowthewallbase). 20 21 Note:InMalaysia,ultimatebondstressisgenerallycalculatedusingcorrelationswithSPT"N"values andvariesfrom3to5N. RecommendedValueforDesignFacingPressureFactors 22 Theallowablenailheadloadisthenthelowestcalculatedvalueforthetwodifferentfailuremodes. 23 Bearingplateconnection Allowablenailloadsupportdiagram 24 Methodology Introduction Thischapterdiscussesthematerialsandbuildingtechniquesusedtobuildsoilnail walls.Wheninstallingsoilnails,twobasicmethodsdependonthereinforcingbarbeingused: Directandindirectinstallationarealsooptions.Atwo-stepmethodisusedtodrillandgrout solidbarsoilnailswith4to8inchesdiameterandattachsoiltoafoundationusingsolidbar soilnails.Ashallowangleofattackiscreatedbyinitiallydrillingholesatashallowangle (usually15degreesfromhorizontal)usingcasedoropen-holemethods(Yuan.,etal,2019). Thesecondstageisinsertingthetendonsandgroutingthemintotheholesinthetendonsthat havebeendrilled.It'shardtoseeaconstructionsitewithoutseeingapileofsolidbardirt nails.Theirtendonlengths,threadtypes,andsteelgradesareallwidelyaccessible,asare severalcorrosionprotectionschemestosuitabroadrangeofapplicationsandsite circumstances.Theyaredrilledandgroutedintothegroundsimultaneouslyusinghollowbar soilnails(HBSNs).Tousethesesoilnails,holesmustbemadeintheground,andgroutmust beusedtofastenthetendonstothesoil.Groutisputintotheholewhileit'sbeingdrilledto keepitfromdryingout.Itwashesdirtoutoftheholeandfillstheannularareabetweenthe tendonandthedrillbitwhenthegroutisinjectedfromportsinasacrificialdrillbit.Drilling techniques,includingrotaryandrotarypercussiondrilling,areoccasionallyemployedin conjunctionwithHBSNs.HBCUsmaybeplacedconsiderablymorerapidlythansolidbar soilnailsinmostsituationsifthesubsurfaceconditionsarefavorable.Thesebarsare especiallyusefulinsoilswhereopendrillholeswouldotherwisecollapseandneedtheuseof temporarycasingtopreserveholestabilityuntilgroutcanbeinjected.HBCUsofferlimited optionsforcorrosionprotection,andqualityassurancestandardsandtestingproceduresare stillbeingdeveloped.TheLimitEquilibriumMethod(LEM)willbeutilizedtoevaluatesoil androckslopestabilityanddamstability,embankmentstability,andretainingwallstability 25 aspartofthisresearch,whichwilluseSlide2v6.0,acommercial2Dslopestabilityprogram developedbyRocscience.Arepresentativecross-sectionofanidealizedslopemustbe createdtoderivemeaningfulconclusionsfromthetwo-dimensionalstudy.Aslopestability analysisforgeotechnicaldesignmustfindtheslipsurfacewiththelowestfeasiblesafety factorifitistobesuccessful.Inthecaseofcircularslipsurfaces,theslipsurfacewiththe lowestFoSmaybedeterminedbyrepeatingtrialsonalargenumberofcircularslipsurfaces. Tolocatetheslipsurfacewiththelowestestimatedfactorofsafety,createagridpatternof centersforafamilyofcircularslipsurfaces.Thenutilizethisgridpatterntoidentifytheslip surface.Automatingthesearchfornoncircularslipismuchmorechallengingwhentheslipis notcircular.Manycomputerapplicationsasktheusertolookforaslicksurfaceby examiningavarietyofsuitabletestslicksurfaces.Itisessentialtousesomediscretionwhen choosingwhichsmearstoexamine.Follow-updiscussionsapplytoproblemsthatarise beforeandaftersoilnailingisused.Theprocessoffindingtheslipsurfacewiththelowest feasiblesafetyfactorisknownasoptimizationfromamathematicalviewpoint.Thismethod necessitatestheformulationofanobjectivefunction(e.g.,safetyfactor)thatincludesa numberofspecifiedvariables(e.g.,slideposition)andanumberofrestrictions.Changingthe variablesputupforthisreasonmayresultinthegoalfunctionhavingitsmaximum(or minimum)value.Theoptimizationprocessmaybeaidedbyabroadrangeofmathematical techniques.Geotechnicalengineeringapplicationshavemadeuseofsomeofthesetechniques, whileothersarestillbeingdeveloped. Inthisresearch,a1:1slope(a45-degreeinclination)willbeinvestigatedwhetheritis naturallyoccurringorartificiallycreated.Inaddition,theslope'sheightandwidthwillbe both10meters,andthesoilwillbemadeupoftwotypesofclay:asiltyclaylayerontopofa claylayerundertheslope'ssurface.SoilshearstrengthwillbecalculatedbyusingtheMohr- Coulombfailurecriterionasfollows: 26 IfTrepresentsshearstrength,nrepresentseffectivestress,andTstandsfortotalstress.The pore-waterpressure,cohesiveness,andfrictionanglearealsodesignatedbytheletterT. Real-worldcircumstancesmayneedtheuseofdrainage,triaxial,ordirectsheartestingto determinethesoil'sstrengthproperties.Itisexpectedthattheanalysiswilltakealongtime; therefore,effectivestresseswillbeused.Becauseofthis,intheshort-termanalysis,the undrainedshearstrengthofthegroundisused(c=cuand0)todeterminehowmuchenergy willbereleasedintheeventofanearthquake. ComponentsofSoilNailWall Soilnailsincludethreadedtendonattachmentstopreventthemfromsnapping.Threads maybeslicedintwoways:intoaspirally-deformedribbing(alsoknownascontinuous threadbars)orintoarawreinforcingbar.Thecutfaceofthebarmustbethreadeda minimumof6in.toallowforproperconnectionofthebearingplateandnut.When creatinganon-threadedbar,keepinmindthatcuttingthreadsreducestheamountofsteelin thethreadedsection.Themajorityofthetime,tendonnonessentialtensilestrengthis60ksi (grade60)or75ksi(grade75)(Grade75).ASTMA615specifiesthatsteeltendonsof grade60or75mustsatisfythecriteria.Certainapplicationsmaybenefitfromusingsoil nailswithtendontensilestrengthsof95ksi(Grade95)and150ksi(Grade150).Ground anchors(Sabatinietal.1999)utilizehigh-gradesteelmoreoftenbecausetheirdesignloads aretypicallymuchgreaterthansoilnails(Su.,etal,2008). Consequently,forconventionalsoilnailinstallations,high-gradesteelmaynotbethemost cost-effectivechoice.Soilnailingmaybepossiblewith95ksi(Grade95)steelbarsiftheir 27 flexibilityiscomparabletolower-gradesteel.ASTMA722specifieshowgrade150steel barsshouldbeproducediftheyaretobeused.AppendixA,TableAdisplaysthesection characteristicsofsolidbartendons.Itisnotuncommontocomeacrosssolidbardirtnails withthesizedesignationsNo.8,9,10,and11.Smallerdiameterbarsareusedbycertain soilnailproducers(uptothenumbers6and7);however,thisisdiscouragedsincesmall diameterbarstendtobendexcessivelyduringhandlingandinstallation,resultinginthe nailsbeingspacedtootightlymakingthesystemlesseffective.Geotechnicalpulloutand thestrengthofthecladdinglimitthemaximumtensileloadofbarswithnominaldiameters of14andabove,makingtheminefficient.Tobesure,theselimitationsonbarsizedon't alwaysapplyeverywhere.Themaximumproductionlengthforthreadedbarsinthesixto fourteen-inchrangeis60feet.Mosttendonstructuresdonothavesplicesorwelds. Couplersmaybeusedtoextendthelengthofbars.Thenominaltensileresistanceofthe barsmustbedevelopedinlinewiththecertificationofthemanufacturer.Solidbarswith threadedendsareseeninFigure3.2. 28 Tendons Threadedsolidbars. Asaresultofthiswiderangeofyieldtensilestrengths,hollowsoilnailingbarsmaybeused inmanysoilnailingapplications(410MPaand620MPainSIUnits).Withanouterdiameter rangingfrom30mmto3inches,hollowbarshavewallthicknessesthatrangefrom0.3to1 inch.Theyarealsoknownasroundbars(7to25mm).Usinglongertendonpieces,custom lengthsmaybecreatedbycuttingandlinkingthemtogether.Tendonsmaybepurchasedin lengthsrangingfrom10to20feet.Sectioncharacteristicsofhollowbartendonscommonly availableonthemarketareshowninTablesA.2throughA.4(AppendixA). PartsoftheConnection Steelcomponentssuchasbearingplates,beveledwashers,hexagonalnuts,washers,and headedstudsareamongthenumerouskindsusedtoconnectdirtnailstothefacing.Fornail- to-first-faceconnection,usethebearingplate,hexnuts,andwashers;fornail-to-last-facing connection,useheadedstuds(BabuandSingh,2008).Abearingplateiscombinedwiththe nailendtotransmittheforceappliedonthefirstshotcretefaceandthesoilbehindthefacing. Certaindirtnailbarmanufacturersprovideforgedbearingplateswithaconcavedrillhole, enablingtheconnectiontobeflexibleineitherdirection.Forthemostpart,contractors 29 positionedthebearingplateagainstthefirstface'sfresh,still-wetshotcrete.Thebearingplate mustbeproperlypositionedinthegroutnottogettoodeeplyembedded. Bearingplatesandnutsareuniformlydistributedbyinsertingbeveledwasherswithanangle thatmatchestheslopeofthenailbetweenthem.Sphericalseatnutsareoftenusedinsteadof hexagonalseatnutstomakealigningthecorrespondingpartseasier.Boltnutsaresnuggedup usingahand-wrench.Oncetheshotcretehasbeenset,usecaretoavoidovertighteningthe nuts.ThereareAASHTOM291/ASTMA563GradeBrequirementsforwashersandnutsin theassembly.Toconnectthebearingplatetothefinalface,four-headedstudsareoften utilized.Finally,thebearingplateisinstalledandtightenedusingthestudsthatwerewelded toit.TheAmericanNationalStandardsInstitute/AmericanWeldingSociety2000mustbe followedwhiledoingstructuralwelding.Thereshouldbeenoughspacebetweenstudsand theouterbordersoftheplatesothattheyarenotweldedanyclosertotheplate.Whilethe diameterofthestudshaftinfluencesthisdistance,it'stypicallybetween1and1.5inches. 30 Mouldandgrout Groutusedinsoilnailingapplicationsinneatcementmixeshasawater/cementratioof0.4- 0.5%,withaspecificgravityof1.8-1.9inneatcementmixes.Duringthegroutpreparation process,specificgravitymeasurementsofneatcementgroutmixesareperformed,andthe findingsareinstantlyaccessible.Ifthecomponentsandmixdesignconsistentlygenerate groutwiththeminimumnecessarystrength,theymaybeusedasaprimaryqualitycontrol measureforneatcementgroutmixtures.Beforeproduction,pre-productioncompression testingongroutcubesproducedfromamixwithaspecificgravitymayaddressthisproblem. Whenitcomestimetoverifythecompressivestrengthofthegrout,unmoldedanduntested cementgroutcubesmaybeformedandtested.Dependingontheproject'sspecificconditions, astrongergroutmaybeneededtolimitgroutleakageintohighlyporousgranularsoilsor badlyfracturedrock.Inthesecases,alessflowablesand/cementgroutmaybeused.Usinga groutthatistoohard,ontheotherhand,canmaketendoninsertiondifficultorimpossible usingconventionalgroutingequipment(TurnerandJensen,2005).Ifathickergroutis neededtocontrolgrouttake-infromthesoil,pre-treatingthegroundbeforeplacingsoilnails maybenecessary.Forexample,asand/cementgroutmix'squalitycannotbecontrolledusing specificgravitymeasurements.Certaingranularsoilswithanopenmatrixandminimal cohesionmaycausedrillholestocollapseandgrouttoleak(forexample,poorlygraded gravel).Thisholdsevenifyou'reworkingwithahardgrout. Toavoidthedrillholecollapsingandtorestrictgroutflowintothehighlyporousearth,it maybenecessarytouseagrout"sock."Thesteelbarandtremiepipearecoveredina geotextilebeforethewholeassemblyisplacedintotheholethathasbeenexcavatedtomake guttersocks.Additivesaren'trequiredinthevastmajorityofcases.Admixturesinthegrout mayreducebleedingandenhanceflowabilitywhilealsodecreasingthewatercontentand delayingthesettingtime.MaterialsmustmeettheAASHTOM194/ASTMC494 31 requirements,becompatiblewiththegrout,andbemixedaccordingtothemanufacturer's specifications.Acceleratorsaren'tpermittedveryoften.Calciumchloride-containing acceleratorsingroutshouldbeavoidedsincetheyincreasethecorrosionpotentialaroundthe tendon. Plasticizersmayhelpyougetthejobdonequickerandmoreeffectivelyifyou'reworkingina hotclimateorifthegrouthastobepumpedoverlongdistances.Plasticizersusedinthegrout mayfrequentlykeepitworkableforuptoanhourafterapplication.Aswellasmakingthe grouteasiertoworkwithandlesspronetocracking,air-entrainmentagentsalsoallowthe grouttoopenup,decreasingtheamountofchemicalandphysicalcorrosionprotection providedbythecement.Thismeansthatonlycircumstanceswherenoothercorrosion preventionmeasuresareavailable(suchasgroutcover)orwherethegroutcoverthickness exceedstheminimumvaluesshouldemployairentrainmentagents.Specialgroutscontain chemicalsthatlimittheshrinkagetominimizecrackingandenhancethebondingstrength betweentwosurfaces.Toensurethatthegroutandbondingpropertiesarenotharmed,testing shouldbedoneonanyadmixturesconsideredforuse.Assoonasthetendonhasbeenplaced inthedrillhole,cementshouldbepouredintoittohelppreventitfromcompressingor collapsing.Tremiemethodsareusedintheseapplicationstoinjectthegroutviaanembedded groutpipe,whichfillswithgroutasitisinjected,ensuringthatallgroutisinjectedbeforethe holecloses.Aregionabovethedrillholeopeningcanneverbefilledwithfreshgroutdueto itsfluidnatureandinclinationinrespecttothedrillholeopening.Whenatemporarycoveris placedinfrontofthedrillhole,itcreatesa"bird'sbeak"shapethatmaybefilledwith additionalgroutorshotcrete,whichispackedinbyhandorappliedduringtheshotcrete facinginstallation.Thisareamustbefilledafterbeingsubjectedtowaterpenetrationand subsequentcorrosiontoprovidefullcoverageandmoistureprotection.Hardplastictubingin the0.75tothe1.0-inchrangeisoftenusedforgroutpipeconstruction.It'sanormal 32 proceduretotakethegrouttubeoutoncethegrouthasbeenapplied.Ontheotherside,some builderschoosetokeepthegrouttubeinplacesinceitdoesn'tsignificantlyaffectthejob.To avoidleaks,thegrouttubeshouldbesealedatthedistalendifitisimpossibletoremoveit. Soilnailswillperformandlastlongeriftubesarefilledbeforeinstallation.Iftubesarenot filled,thismustbetakenintoaccountbeforesoilnailsareplaced. Centralizers TendonrupturesmaybepreventedusingPVCSchedule20orSchedule40centralizersand othersyntheticmaterialsthatarenotdamagingtothetendon.HBSNsareusedin combinationwithsteelcentralizers(Lee.,etal,2021).Toensurethatthetendoniscompletely coveredwithaminimumgroutthickness,centralizersmustbeplacedatvariousplacesalong thelengthofeachsolidbarorHBSN.Theyarepositionedasindicatedinthepictureat regularintervalsthroughoutthenail'slength,notmorethan10feetapartandapproximately 1.5feetawayfromeitherendofthenail.Tobesuccessful,centralizersmustbeconnected firmlytothetendonsandlargeenoughtoallowforthefollowing:Assemblingatremiepipe, enablinggrouttoflowfreely,andplacingthetendononeinchfromthedrillhole'scenterare allstepsinthedrillingprocess. MaterialsandComponentsResistanttoCorrosion Additionalcorrosionprotectiondevicesareusedtothetendonsinadditiontothecement grout,whichshieldsthemfrombothphysicalandchemicalharm.Thefinalstepistogrout theannulusbetweenthesheathandholeafterplacingtheencasedbarintheholeusingthe tremiemethodspreviouslydescribedindetail.Epoxycoatingsfusion-bondedtosolidbarsare anoption.Dielectricepoxycoatingavoidscorrosionbyblockingelectriccurrentsthatmight otherwiseflowthroughit.Whenusingfusion-bondedepoxycoating,besuretoadheretothe ASTMA775standard.Epoxycoatingforbarscomesinawiderangeoftypesand thicknesses.Green,gray,andpurplearethepossiblehuesforthecoatings.Withitsabilityto 33 bendandconformtovariousshapes,thegreenepoxycoatingisexcellentforsteelreinforcing bars.Epoxycoatingsingrayandpurplearelessflexiblethaningreenones,butgreenepoxy coatingsaremorechemicallyresistant.Formarineorharshcircumstances,purpleepoxy paintisbetterthanclearepoxycoating.Youmaygalvanizebothsolidandhollowtendonsas wellastheirhardwareusinghot-dipgalvanizing. TheWall'sSurface Tendonconnectionsareconstructedontheexcavationfaceorslopesurfacetoconnecttoa facingsystem.Dependingontheapplication,facingsareoftenmadeupoftwolayers:initial shotcretefacingandshotcreteorCIPconcretefinalfacing.Whileexcavatingandnailing,the initialfacing'sfunctionistosupporttheexposedsoil,createaninitialconnectionbetween them,andofferprotectionagainsterosionandsloughingattheexcavationfacethroughout thoseprocesses.Despiteperformingthesamefunctionsasthefirstfacing,thefinalface benefitsfrommeetingtheproject'saestheticrequirements.Otherimportantaspectsmustbe consideredinthefinalfacedesignandlong-termcorrosionandclimatechanges. Removalofwastematerials Toreducetheamountofwaterpressurebehindthewallfacing,verticalgeocompositestrip drains(referredtoasstripdrainsinthistext)areinstalled(Lin.,etal,2017).Thedrainage coreofageocompositestripdrainislinkedtoorencapsulatedbyafiltrationgeotextile, whichprovidesfiltrationforthedrainagecore.Inthedrainagecore,syntheticpolymerslike polypropyleneandpolyesteraremixedwithPVC,polyolefin,andpolystyrenetocreatea cohesivestructure.Thecore'scompressivestrengthmustbe40poundspersquareinchor moreafterASTMD1621ProcedureAtesting.AccordingtoASTMD4716,adrainagecore withageotextilefullysurroundingitmusthaveaflowrateof0.1gallonspersecondperfoot ofstripwidthwhenmeasured.Drainagecomponentsareincludedinthestripdrains.Oncethe drainsarefitted,watermayflowfromthestripstotheoutsideofthewall.Dependingonthe 34 application,itisalsopossibletoconstructapipedrainatthewall'sbaseortouseweepholes todischargethroughthewall'sfaceandtoe. Installingandfinishingthenailsandgrout Tocompletetheprocedure,agrout-filledtremiepipeisusedtofillupthedrillholeoncethe tendonisplaced.Thegroutpipemustbeinsertedintothebottomofthedrillhole,andthe groutmustbeinjecteduntilthecavityisfilled.Astrongbonddevelopsbetweenthetendon andthesurroundingearthwhenthegroutsolidifies.Inmanycases,soilnailingisafeasible andcost-effectivealternativetogravitygroutingbecauseofthehighbondstrengthsthatmay beachieved.Grout'senhancedbondstrengthisaconsequenceofgreaterconfiningpressures, soilcompaction,increasedsoil-groutinterlocking,andanincreaseingrouteffectivediameter comparedtostrengthachievedwithgravitygrouting.Forfine-grainedsoils,pressuregrouting throughthecasingisseldomusedsincethebondresistanceimprovesonlylittlewhenthe soilsaremoist.Ifappropriateinstallationmethodsarenotfollowed,itisconceivablethatthe designbondresistancewillnotbeachieved.Asignificantreductioninbondresistancemay becausedbyinadequateremovalofdrillholecuttings.Excessivemechanicalcleaningofthe drillholemaycausetheclaytoberemoldedinclayeysoilswithmoderateplasticity,resulting inbondresistancevaluesthatareconsiderablylowerthanthoseanticipatedundercontrolled circumstancesforthesesoils.Toavoidfutureproblems,makesurethedrillholeisascleanas possiblebeforecontinuing. 35 ResultsandDiscussion . Usingthismethod,themodel'sboundaries,whichareplacedatadistanceof15metersfrom boththeslope'stoeandcrown,willnotobstructthesearchforkeyfailuresurfaces.The figureshowstheground'soriginalshapebeforeSlide2wasadded. 36 AslongastheFoSismorethantheminimumpermittedby-laws,standards,andregulations whilealsotakingintoaccounttheproject'ssignificance,theslopeisconsideredstable,andno furtherstepsneedtobedonetokeepitstable(Liu.,etal,2021).Conversely,iftheFoSis foundtobeinadequate,supportmeasuresmustbeimplemented.Fortheslopetobe consideredstableinthesimplifiedcase,itmusthaveanindicativeFoSgreaterthan1.25tobe stable. Slide2allowsthesimultaneousapplicationofseverallimitequilibriummethods(e.g., Ordinary,Bishop,Janbu,Spencer,Morgenstern-Price).Inthispart,we'llusetheBishopand Spencermethodsasanexample.Themaximumnumberofiterationsissetat50,andthe maximumnumberofslicespersurfaceevaluatedis30.Temperatureandhumidityandthe timeofyearmayhaveasignificantimpactonthelevelofthegroundwatertable.Consider thefollowingtwopossibilitiesforthelevelofthegroundwater: Firstandforemost,whenthegroundwatertableislow,thefailuresurfacesarenotinfluenced. Anunfavorableconditionwhenthebulkofthelandissituatedbelowthewatertable; 37 Secondly,whenconditionsaresaturated,pore-waterpressurebuildsup,reducingthe ground'sshearstrengthand,consequently,theslope'sForceonSlope(FoS).We'llcallthe firstsetofcircumstances"Dryconditions,"andthesecondsetofcircumstances"Partially saturatedconditions"tokeepthingssimple. a)Dryandb)Partiallysaturatedconditions Theanalysisshouldconsideranyadditionalexternalloadsthatmayaffecttheslope'sstability atthistime.Therearen'tanyexternalloadstoconsiderinthiscase.Thefailuresurfacesare thencalculatedusingeitheranautomatedgridorahumangridgeneratedusingSlide2.To ensurethatthenecessarysurfaceisincludedinthegrid,provideextraspacewhile constructingthegrid. Asaresultoftheproblembeingclearlystated,itcannowbeginthecomputationprocess.For slopesthataredryorsomewhatwet,usingtheBishopandSpencermethods,thecritical searchsurface(FoS). 38 Thereisaconsistentcriticalsurfaceinallcases(bothdryandpartlywetcircumstances). Aboutthreemetersbelowtheslope'scrown,itstartsandendsattheslope'stoeareitsstarting andendingpoints. Giventhegroundwaterconditions,thesafetyfactorscomputedbytheBishoporSpencer techniquesprovidevaluesthatareverynearlyidentical(dryorpartiallysaturated(Tokhi,H., 2016). 39 TheprocessofstabilizingaslopeisreferredtoasSlopeStabilization. Anengineermustcontinuallyensurethataslopeisstable,evenintheworst-casescenario. Stabilizationandexpansionoftheslope'sfieldofview(FoS)havebeenthesubjectofmany researchanddevelopmenteffortsovertheyears.Therearemanyinstancesofthesestrategies inaction,someofwhichdeservespecialmention.Someexamplesincludeinstallingdrainage features,constructingretainingwallsorbuttresses,usinggeotextiles,andanchoring structures. TheaimofemployingsupportmeasuresistoenhancetheFoSwhileusingtheabsolute minimumofnecessaryandeasilyavailableresourceswhiledesigninganoptimalsolution.As aresult,decidingonthebestsupportmethodsisdependentontheparticularcircumstances. ToimprovetheFOSoftheexampleslope,itwillberequiredtouseagroundstabilizing techniqueknownassoilnailing.Holesaredrilledintheslope'sfacetousethismethod,and steelbarsareinsertedintotheholes.Groutisusedtofillingtheholesoncetheyhavebeen cleanedout.Insoftsoilsandweakrockformations,soilnailsareoftenutilizedaspassive supportcomponentstokeepslopesstable.Amongtherequirementsforeachsoilnailarethe followingtechnicalcriteria: Generally,soilnailsshouldnotbelongerthan15metersduetothedifficultiesincreatingand maintainingthestabilityofthedrillholes.Length:Soilnailsareusuallybetween0.8and 1.2timeshigherthantheslope.Anormalsoilnailweighs0.81.2timesasmuchastheslope it'sattachedtomaximumtensileloadsforsoilnailsaregovernedbythematerial's(steel's) propertiesandthesoilnail'scross-sectionalarea's(cross-sectionalareaofthenail). 40 Todeterminethemaximumloadthatadirtnailplatecansupportatanyonemoment,use PlateCapacity.Thesoilnailshouldhavethegreatestshearandcompressioncapabilitiesitis capableofwithoutfailing,inadditiontotheshearandcompressioncapacities.theforcewith whichsoilnailsmaybeyankedoutofthegroundwhentheyarepulledoutAgridofsoil nailswillbeconstructedtosupportaslopingsurface,andotherfeatureswillneedtobe determined.Youknowwhotheyare: Out-of-planespacinginthethirddimensionreferstothedistanceinmetersbetween eachdirtnail(perpendiculartothe2Dcross-sectionalview). Soilnailsarespacedlongitudinally,horizontally,orvertically,dependingonwhether they'reusedinlandscaping. Todeterminetheangleoforientationofasoilnail,lookathowmuchitpointsaway fromthehorizontalplane. Importantconsiderationsincludethegeographicaldistributionofsoilnailsandthe slope'sstartingandendingpointsofsupportmeasures. Forthesimpleexampleanalysisshownabove,theassumedvaluesofthe characteristicsmentionedabovewereusedalongwiththestudy'sfindings,. 41 howsoilnailscanstabilizeaslopinggroundsurface.Foursoilnailsareassumedtobe presentinthe2Dcross-sectionalregionpermeter(inthethirddimension). 42 Asaresultoftheresearch,thefollowingfindingshavebeendrawn: ItisdeterminedthattheassistancemeasuresaresuitableduetoanewFoSthatconsidersboth theBishopandSpencerapproaches.Bothmethodsgeneratethesamecriticalfailuresurface. Itislongeranddeeperthanthecriticalfailuresurfacethatisderivedbyassumingan unreinforcedslopebecauseitdoesnotconnectwiththesoilnails.IntheBishopandSpencer techniques,soilnailsincreasedtheForceofSlope(FoS)by59%and61%,respectively,after placingthemontheslope.4.Aspartoftheoverallassessment,anupdatedFoSunderdry conditionsisalsocomputed.Itisfairtoassumethattheslopewillbesteadyevenindry conditionssincetheprecautionsareadequateevenwhenitispartiallywet.Despitethis, figuringoutitsFoSiscriticalforcomparison.Thisstudy'sresultsmaybeseeninFigures6a and6bandthetablebelow. UsingBishopandSpencertechniques,supportmeasuresincreasedry-weathersafetyby59 and60percent,resultinginhigherfactorsof60percentoverall.Thisexamplestudy'ssupport methodsmaybeemployedtostabilizetheslopeifit'sdeterminedthatthegroundwater conditionsaresuitable. Scenario1NoSupports TherewerenosignificantdifferencesbetweenScenario1withandwithoutSupportsand 43 Scenario1withSupports.Inthisexample,theslip-and-fallsurfaceswithaFactorofSafety oflessthan1.5areidentifiedusingtheSafetyMaptool(orangecolor).Soilnailsmustreach beyondtheslipsurfacefromtheslopefacetobeeffective. Scenario2Low-AngleSoilNails(15) Below,you'llseetheresultsofScenario2:LowAngleNails.Fivefeetvertically,sixfeet horizontally,and15degreestotheleftandright,they'rearrangedinasquarepattern. Scenario3High-AngleSoilNails(53) 44 Scenario3NailsataHighAngle(53)presentstheresultsintheaccompanyinggraph.The nailsareplaced5feetapartinaverticalrowandinclined53degreestowardtheearth's surface.Accordingtotheresults,usinghigh-anglesoilnailsreducesembedmentduration whileincreasingthesupports'capacitytoproducemoreresistingforceintheoriented direction.Theverticalsupportforcegeneratesadestabilizingmomentaroundthesliding mass'scenterofrotation,addingtotheinstability.SotheFactorofSafetyissmallerthanif thenailswereshallower,whichisabenefit. Scenario4RocscienceRedesign(15) FollowingisagraphicdepictingtheresultsofScenario4RocscienceRedesign(15).A15- degreeangletothegroundseparateseachnail,spaced5feetverticallyand6feethorizontally. LargerdirtnailswereutilizedtoimprovetheirperformancetoachieveaFactorofSafety greaterthan1.5onallslicksurfaces. 45 References Byrne,R.J.,Cotton,D.,Porterfield,J.,Wolschlag,C.andUeblacker,G.,1996.Manualfor designandconstructionmonitoringofsoilnailwalls. 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