Abutments, retaining Walls, and Reinforced Slopes

Geotechnical Design Manual M 46-03 Abutments,Retaining Walls, and Reinforced Slopes December 2006 Chapter 15-1

Chapter 15 Contents15.1 Introduction 15-5

15.2 Definitions 15-6

15.3 Required Information 15-715.3.1 SiteDataandPermits 15-715.3.2 GeotechnicalDataNeededforRetainingWallandReinforcedSlopeDesign15-715.3.3 SiteReconnaissance 15-915.3.4 FieldExplorationRequirements 15-10

15.3.4.1 Exploration Type, Depth, and Spacing 15-1115.3.4.2 WallsandSlopesRequiringAdditionalExploration 15-12

15.3.4.2.1 SoilNailWalls 15-1215.3.4.2.2 WallswithGroundAnchorsorDeadmenAnchors 15-1215.3.4.2.3 WallorSlopeswithSteepBackSlopesorSteepToeSlopes 15-12

15.3.5 Field,Laboratory,andGeophysicalTestingforAbutments, RetainingWalls,andReinforcedSlopes 15-1315.3.6 Groundwater 15-14

15.4 GeneralDesignRequirements 15-1415.4.1 DesignMethods 15-1415.4.2 SpecialRequirements 15-15

15.4.2.1 TieredWalls 15-1515.4.2.2 Back-to-BackWalls 15-1515.4.2.3 WallsonSlopes 15-1615.4.2.4 MSEWallSupportedAbutments 15-1615.4.2.5 MinimumEmbedment 15-1615.4.2.6 ServiceabilityRequirements 15-1715.4.2.7 Active,Passive,At-restEarthPressures 15-1815.4.2.8 SurchargeLoads 15-1815.4.2.9 SeismicEarthPressures 15-1815.4.2.10 Liquefaction 15-2015.4.2.11 Overall Stability 15-2015.4.2.12 Wall Drainage 15-2015.4.2.13 Utilities 15-2115.4.2.14 GuardrailandBarrier 15-21

15.5 SpecificDesignRequirements 15-2115.5.1 AbutmentsandStandardPlanWalls 15-2115.5.2 NongravityCantileverandAnchoredWalls 15-21

15.5.2.1 NongravityCantileverWalls 15-2215.5.2.2 Anchored/BracedWalls 15-2215.5.2.3 PermanentGroundAnchors 15-2315.5.2.4 Deadmen 15-26

Abutments, Retaining Walls, and Reinforced Slopes Geotechnical Design Manual M 46-03 Chapter 15-2 December 2006

Abutments, Retaining Walls, and Reinforced Slopes

Page15.5.3 MechanicallyStabilizedEarthWalls 15-28

15.5.3.1 InternalStabilityUsingK-StiffnessMethod 15-2815.5.3.1.1 K-StiffnessMethodLoadsandLoadFactors 15-2815.5.3.1.2 K-StiffnessMethodResistanceFactors 15-3015.5.3.1.3 SafetyAgainstStructuralFailure(InternalStability) 15-3115.5.3.1.4 StrengthLimitStateDesignforInternalStability UsingtheK-StiffnessMethodGeosyntheticWalls 15-3815.5.3.1.5 StrengthLimitStateDesignforInternalStability UsingtheK-StiffnessMethodSteelReinforcedWalls 15-4115.5.3.1.6 SeismicDesignforInternalStabilityUsingthe K-StiffnessMethod 15-4315.5.3.1.7 DesignSequenceConsiderationsfortheK-StiffnessMethod 15-43

15.5.4 PrefabricatedModularWalls 15-4415.5.5 RockWalls 15-4415.5.6 ReinforcedSlopes 15-4415.5.7 SoilNailWalls 15-45

15.6 Temporary CutSlopesandShoring 15-4615.6.1 Overview 15-4615.6.2 GeotechnicalDataNeededforDesign 15-4715.6.3 GeneralDesignRequirements 15-48

15.6.3.1 DesignProcedures 15-4815.6.3.2 SafetyFactors/ResistanceFactors 15-4815.6.3.3 DesignLoads 15-4915.6.3.4 DesignPropertySelection 15-49

15.6.4 SpecialRequirementsforTemporaryCutSlopes 15-5015.6.5 PerformanceRequirementsforTemporaryShoringandCutSlopes 15-5115.6.6 SpecialDesignRequirementsforTemporaryRetainingSystems 15-52

15.6.6.1 FillApplications 15-5215.6.6.1.1 MSEWalls 15-5215.6.6.1.2 PrefabricatedModularBlockWalls 15-53

15.6.6.2 CutApplications 15-5315.6.6.2.1 TrenchBoxes 15-5315.6.6.2.2 SheetPiling,withorwithoutGroundAnchors 15-5415.6.6.2.3 SoldierPileswithorwithoutGroundAnchors 15-5415.6.6.2.4 PrefabricatedModularBlockWalls 15-5515.6.6.2.5 BracedCuts 15-5515.6.6.2.6 SoilNailWalls 15-55

15.6.6.3 UncommonShoringSystemsforCutApplications 15-5515.6.7 ShoringandExcavationDesignSubmittalReviewGuidelines 15-56

15.7 References 15-57

Geotechnical Design Manual M 46-03 Abutments, Retaining Walls, and Reinforced Slopes December 2006 Chapter 15-3


PageAppendices 15-58PreapprovedWallAppendices 15-59Appendices 15-56

15-A PreapprovedProprietaryWallandReinforcedGeneralDesign Requirements 15-A15-B PreapprovedProprietaryWall/ReinforcedSlopeDesignand ConstructionReviewChecklist 15-B15-C HITECEarthRetainingSystemsEvaluationforMSEWalland ReinforcedSlopeSystems,asModifiedforWSDOTUse:Submittal Requirements 15-C15-D PreapprovedProprietaryWallSystems 15-D15-E DescriptionofTypicalTemporaryShoringSystemsand SelectionConsiderations 15-E

PreapprovedWallAppendix:SpecificRequirementsandDetailsforLBFoster RetainedEarthConcretePanelWalls 15-1

PreapprovedWallAppendix:SpecificRequirementsandDetailsforEureka ReinforcedSoilConcretePanelWalls 15-11

PreapprovedWallAppendix:SpecificRequirementsandDetailsforHilfiker WeldedWireFacedWalls 15-15

PreapprovedWallAppendix:SpecificRequirementsandDetailsfor KeySystemIWalls 15-21

PreapprovedWallAppendix:SpecificRequirementsandDetailsforTensar MESAWalls 15-31

PreapprovedWallAppendix:SpecificRequirementsandDetailsforT-WALL (TheNeelCompany) 15-51

PreapprovedWallAppendix:SpecificRequirementsandDetailsforReinforced Earth(RECO)ConcretePanelWalls 15-67

PreapprovedWallAppendix:SpecificRequirementsandDetailsforSSL ConcretePanelWalls 15-117

PreapprovedWallAppendix:SpecificRequirementsandDetailsforTensar ARESWalls 15-125

PreapprovedWallAppendix:SpecificRequirementsandDetailsforNelsonWalls 15-145

PreapprovedWallAppendix:SpecificRequirementsandDetailsforTensar WeldedWireFormWalls 15-151

Geotechnical Design Manual M 46-03 Abutments,Retaining Walls, and Reinforced Slopes December 2006 Chapter 15-5

Chapter 15 Abutments, Retaining Walls, and Reinforced Slopes

15.1 IntroductionAbutmentsforbridgeshavecomponentsofbothfoundationdesignandwalldesign.Thischapteraddressestheearthpressuresactingontheabutmentsaswellasretainingwallsandreinforcedslopes.Retainingwallsandreinforcedslopesaretypicallyincludedinprojectstominimizeconstructioninwetlands,towidenexistingfacilities,andtominimizetheamountofrightofwayneededinurbanenvironments.Projectsmodifyingexistingfacilitiesoftenneedtomodifyorreplaceexistingretainingwallsorwidenabutmentsforbridges.Allabutments,walls,andreinforcedslopeswithinWSDOTrightofwayshallbedesignedandconstructedinaccordancewithAASHTOrequirementsandthismanual.

Retainingwallsandreinforcedslopeshavemanybenefitsassociatedwiththeiruse.Unfortunately,therealsotendstobeconfusionregardingwhentheyshouldbeincorporatedintoaproject,whattypesareappropriate,howtheyaredesigned,whodesignsthem,andhowtheyareconstructed.TherollsandresponsibilitiesofthevariousWSDOTofficesandthoseoftheDepartmentsconsultantsfurtherconfusetheissueofretainingwallsandreinforcedslopes,asmanyoftherollsandresponsibilitiesoverlaporchangedependingonthewalltype.Allabutments,retainingwalls,andreinforcedslopeswithinWSDOTRightofWayorwhoseconstructionisadministeredbyWSDOTshallbedesignedinaccordancewiththeWSDOTGeotechnicalDesignManual(GDM)andthefollowingdocuments:

WSDOT LRFD Bridge Design Manual WSDOT Design Manual M22-01 WSDOT Standard Plans for Road, Bridge, and Municipal Construction M21-01 AASHTO LRFD Bridge Design Specifications, U.S.

Themostcurrentversionsoreditionsoftheabovereferencedmanualsincludingallinterimsordesignmemorandamodifyingthemanualsshallbeused.Inthecaseofconflictordiscrepancybetweenmanuals,thefollowinghierarchyshallbeused:Thosemanualslistedfirstshallsupercedethoselistedbelowinthelist.

ThefollowingmanualsprovideadditionaldesignandconstructionguidanceforretainingwallsandreinforcedslopesandshouldbeconsideredsupplementarytotheWSDOT GDMandthemanualsanddesignspecificationslistedabove:

Lazarte,C.A.,Elias,V.,Espinoza,R.D.,Sabatini,P.J.,2003.GeotechnicalEngineeringCircularNo.7,SoilNailWalls,U.S.DepartmentofTransportation,FederalHighwayAdministration, FHWA-IF-03-017,305pp.

Porterfield,J.A.,Cotton,D.A.,Byrne,R.J.,1994,SoilNailWalls-DemonstrationProject103,SoilNailingFieldInspectorsManual,U.S.DepartmentofTransportation,FederalHighway Administration,FHWA-SA-93-068,86pp.

Cheney,R.,andChassie,R.2000.SoilsandFoundationsWorkshopReferenceManual.Washington,DC,NationalHighwayInstitutePublicationNHI-00-045,FederalHighwayAdministration.



Elias,V.,andChristopher,B.R.,andBerg,R.R.,2001,MechanicallyStabilizedEarthWallsandReinforcedSoilSlopes-DesignandConstructionGuidelines,No.FHWA-NHI-00-043,FederalHighwayAdministration,394pp..

Sabatini,P.J.,Pass,D.G.,andBachus,R.C.,1999,GeotechnicalEngineeringCircularNo.4,GroundAnchorsandAnchoredSystems,FHWA-IF-99-015,281pp.

15.2 DefinitionsThevariouswallsandwallsystemscanbecategorizedbasedonhowtheyareincorporatedintoconstructioncontracts.StandardWallscomprisethefirstcategoryandaretheeasiesttoimplement.StandardwallsarethosewallsforwhichstandarddesignsareprovidedintheWSDOTStandardPlans.TheinternalstabilitydesignandtheexternalstabilitydesignforoverturningandslidingstabilityhavealreadybeenaddressedintheStandardPlanwalldesign,andbearingresistance,settlement,and overall stabilitymustbedeterminedforeachstandard-designwalllocation.Allotherwallsarenonstandard,astheyarenotincludedintheStandardPlans.

Nonstandardwallsmaybefurthersubdividedintoproprietaryornonproprietary.Nonstandard,proprietarywallsarepatentedortrademarkedwallsystemsdesignedandmarketedbyawallmanufacturer.Thewallmanufacturerisresponsibleforinternalandexternalstability,exceptbearingresistance,settlement,andoverallslopestability,whicharedeterminedbythegeotechnicaldesigner.Nonstandard,nonproprietarywallsarenotpatentedortrademarkedwallsystems.However,theymaycontainproprietaryelements.Anexampleofthiswouldbeagabionbasketwall.Thegabionbasketsthemselvesareaproprietaryitem.However,thegabionmanufacturerprovidesgabionstoaconsumer,butdoesnotprovideadesignedwall.Itisuptotheconsumertodesignthewallanddeterminethestablestackingarrangementofthegabionbaskets.Nonstandard,nonproprietarywallsarefullydesignedbythegeotechnicaldesignerand,ifstructuraldesignisrequired,bythestructuraldesigner.Reinforcedslopesaresimilartononstandard,nonproprietarywallsinthatthegeotechnicaldesignerisresponsibleforthedesign,butthereinforcingmaybeaproprietaryitem.

AnumberofproprietarywallsystemshavebeenextensivelyreviewedbytheBridgeandStructuresOfficeandtheHQGeotechnicalDivision.ThisreviewhasresultedinWSDOTpreapprovingsomeproprietarywallsystems.ThedesignproceduresandwalldetailsforthesepreapprovedwallsystemshavebeenagreeduponbetweenWSDOTandtheproprietarywallmanufacturers.Thisallowsthemanufacturerstocompetitivelybidaparticularprojectwithouthavingadetailedwalldesignprovidedinthecontractplans.Notethatproprietarywallmanufacturersmayproduceseveralretainingwalloptions,andnotalloptionsfromagivenmanufacturerhavebeenpreapproved.TheBridgeandStructuresOfficeshallbecontactedtoobtainthecurrentlistingofpreapprovedproprietarysystemspriortoincludingsuchsystemsinWSDOTprojects.Alistingofthepreapprovedwallsystems,asofthecurrentpublicationdateforthismanual,isprovidedinWSDOT GDM Appendix 15-D.SpecificpreapproveddetailsandsystemspecificdesignrequirementsforeachwallsystemarealsoincludedasappendicestoWSDOT GDM Chapter 15. Incorporationofnonpreapprovedsystemsrequiresthewallsuppliertocompletelydesignthewallpriortoadvertisementforconstruction.Allofthemanufacturersplansanddetailswouldneedtobeincorporatedintothecontractdocuments.Severalmanufacturersmayneedtobecontactedtomaintaincompetitivebidding.MoreinformationisavailableinChapters510and1130oftheWSDOTDesignManual M22-01.



Ifitisdesiredtouseanon-preapprovedproprietaryretainingwallorreinforcedslopesystem,reviewandapprovalforuseofthewallorslopesystemonWSDOTprojectsshallbebasedontheHITECSubmittalProtocolChecklistforwalls,asmodifiedforWSDOTuse,providedinWSDOT GDM Appendix 15-C.Thewallorreinforcedslopesystem,anditsdesignandconstruction,shallmeettherequirementsprovidedinthismanual,includingWSDOT GDM Appendix 15-A.ForMSEwalls,thewallsuppliershalldemonstrateinthewallsubmittalthattheproposedwallsystemcanmeetthefacingperformancetolerancesprovidedinWSDOT GDM Appendix 15-Athroughcalculation,constructiontechnique,andactualmeasuredfullscaleperformanceofthewallsystemproposed.

15.3 RequiredInformation15.3.1 Site Data and PermitsTheWSDOTStateDesignManualdiscussessitedataandpermitsrequiredfordesignandconstruction.Inaddition,Chapters510and1130providespecificinformationrelatingtogeotechnicalworkandretainingwalls.

15.3.2 Geotechnical Data Needed for Retaining Wall and Reinforced Slope DesignTheprojectrequirements,site,andsubsurfaceconditionsshouldbeanalyzedtodeterminethetypeandquantityofinformationtobedevelopedduringthegeotechnicalinvestigation.Itisnecessaryto:

Identifyareasofconcern,risk,orpotentialvariabilityinsubsurfaceconditions Developlikelysequenceandphasesofconstructionastheymayaffectretainingwallandreinforced

slopeselection

Identifydesignandconstructabilityrequirementsorissuessuchas: - Surcharge loads from adjacent structures - Easements

- Backslope and toe slope geometries - Excavation limits - Right of way restrictions - Wetlands - Materials sources - Construction Staging

Identifyperformancecriteriasuchas: - Tolerable settlements for the retaining walls and reinforced slopes

- Tolerable settlements of structures or property being retained - Impact of construction on adjacent structures or property - Long-term maintenance needs and access

Identifyengineeringanalysestobeperformed: - Bearing resistance - Global stability

- Settlement - Internal stability Identifyengineeringpropertiesandparametersrequiredfortheseanalyses Identifythenumberoftests/samplesneededtoestimateengineeringproperties



Table 15.1providesasummaryofinformationneedsandtestingconsiderationsforretainingwallsandreinforcedslopedesign.

GeotechnicalIssues

EngineeringEvaluations

RequiredInformationfor

AnalysesFieldTesting LaboratoryTesting

FillWalls/ReinforcedSoilSlopes

internalstability external

stability limitations

onrateofconstruction

settlement horizontal

deformation? lateralearth

pressures? bearing

capacity? chemical

compatibilitywithsoil,groundwater,andwallmaterials?

porepressuresbehindwall

borrowsourceevaluation(availablequantityandqualityofborrowsoil)

liquefaction potentialfor

subsidence(karst,mining,etc.)

constructability scour

subsurfaceprofile(soil,groundwater,rock)

horizontalearthpressurecoefficients

interfaceshearstrengths

foundationsoil/wallfillshearstrengths?

compressibilityparameters?(includingconsolidation,shrink/swellpotential,andelasticmodulus)

chemicalcompositionoffill/foundationsoils?

hydraulicconductivityofsoilsdirectlybehindwall?

time-rateconsolidationparameters?

geologicmappingincludingorientationandcharacteristicsofrockdiscontinuities?

designfloodelevations

seismicity

SPT CPT dilatometer vaneshear piezometers testfill? nucleardensity? pullouttest

(MSEW/RSS) rockcoring

(RQD) geophysical

testing

1-DOedometer triaxialtests unconfined

compression directsheartests grainsize

distribution AtterbergLimits specificgravity pH,resistivity,

chloride,andsulfatetests?

moisturecontent? organiccontent moisture-density

relationships hydraulic

conductivity



GeotechnicalIssues

EngineeringEvaluations

RequiredInformationfor

AnalysesFieldTesting LaboratoryTesting

CutWalls internalstability external

stability excavation

stability dewatering chemical

compatibilityofwall/soil

lateralearthpressure

down-dragonwall

porepressuresbehindwall

obstructionsinretainedsoil

liquefaction seepage potentialfor

subsidence(karst,mining,etc.)

constructability

subsurfaceprofile(soil,groundwater,rock)

shearstrengthofsoil

horizontalearthpressurecoefficients

interfaceshearstrength(soilandreinforcement)

hydraulicconductivityofsoil

geologicmappingincludingorientationandcharacteristicsofrockdiscontinuities

seismicity

testcuttoevaluatestand-uptime

wellpumpingtests

piezometers SPT CPT vaneshear dilatometer pullouttests

(anchors,nails) geophysical

testing

triaxialtests unconfined

compression directshear grainsize

distribution AtterbergLimits specificgravity pH,resistivity

tests organiccontent hydraulic

conductivity moisturecontent unitweight

Table15.1 Summaryofinformationneedsandtestingconsiderations.

WSDOT GDM Chapter 5coversrequirementsforhowtheresultsfromthefieldinvestigation,thefieldtesting,andlaboratorytestingaretobeusedtoestablishpropertiesfordesign.Thespecifictestsandfieldinvestigationrequirementsneededforfoundationdesignaredescribedinthefollowingsections.

15.3.3 Site ReconnaissanceForeachabutment,retainingwall,andreinforcedslope,thegeotechnicaldesignershouldperformasitereviewandfieldreconnaissance.Thegeotechnicaldesignershouldbelookingforspecificsiteconditionsthatcouldinfluencedesign,construction,andperformanceoftheretainingwallsandreinforcedslopesontheproject.Thistypeofreviewisbestperformedoncesurveydatahasbeencollectedforthesiteanddigitalterrainmodels,cross-sections,andpreliminarywallprofileshavebeengeneratedbythecivilengineer(e.g.,regionprojectengineer).Inaddition,thegeotechnicaldesignershouldhaveaccesstodetailedplanviewsshowingexistingsitefeatures,utilities,proposedconstruction,andrightorwaylimits.Withthisinformation,thegeotechnicaldesignercanreviewthewall/slopelocationsmakingsurethatsurveyinformationagreesreasonablywellwithobservedsitetopography.Thegeotechnicaldesignershouldobservewhereutilitiesarelocated,astheywillinfluencewherefieldexplorationcanoccurandtheymayaffectdesignorconstructability.Thegeotechnicaldesignershouldlookforindicationsofsoftsoilsorunstableground.Itemssuchashummockytopography,seepsorsprings,pistolbuttedtrees,andscarps,eitheroldornew,needtobeinvestigatedfurther.Vegetativeindicatorssuchasequisetum(horsetails),cattails,blackberry,oraldercanbeusedtoidentifysoilsthatarewetorunstable.Alack



ofvegetationcanalsobeanindicatorofrecentslopemovement.Inadditiontoperformingabasicassessmentofsiteconditions,thegeotechnicaldesignershouldalsobelookingforexistingfeaturesthatcouldinfluencedesignandconstructionsuchasnearbystructures,surchargeloads,andsteepbackortoeslopes.Thisearlyindesign,itiseasytooverlookitemssuchasconstructionaccess,materialssources,andlimitsofexcavation.Thegeotechnicaldesignerneedstobecognizantoftheseissuesandshouldbeidentifyingaccessandexcavationissuesearly,astheycanaffectpermitsandmaydictatewhatwalltypemayormaynotbeused.

15.3.4 Field Exploration RequirementsAsoilinvestigationandgeotechnicalreconnaissanceiscriticalforthedesignofallabutments,retainingwalls,orreinforcedslopes.Thestabilityoftheunderlyingsoils,theirpotentialtosettleundertheimposedloads,theusabilityofanyexistingexcavatedsoilsforwall/reinforcedslopebackfill,andthelocationofthegroundwatertablearedeterminedthroughthegeotechnicalinvestigation.Allabutments,retaining,wallsandreinforcedslopesregardlessoftheirheightrequireaninvestigationoftheunderlyingsoil/rockthatsupportsthestructure.AbutmentsshallbeinvestigatedlikeotherbridgepiersinaccordancewithWSDOT GDM Chapter 8.

Retainingwallsandreinforcedslopesthatareequaltoorlessthan10feetinexposedheightasmeasuredverticallyfromwallbottomtotoporfromslopetoetocrest,asshowninFigure 15.1,shallbeinvestigatedinaccordancewiththismanual.Forallretainingwallsandreinforcedslopesgreaterthan10feetinexposedheight,thefieldexplorationshallbecompletedinaccordancewiththeAASHTOLRFDBridgeDesignSpecificationsandthismanual.

Figure15.1 Exposedheight(H)foraretainingwallorslope.

Explorationsconsistingofgeotechnicalborings,testpits,handholes,oracombinationthereofshallbeperformedateachwallorslopelocation.Geophysicaltestingmaybeusedtosupplementthesubsurfaceexplorationandreducetherequirementsforborings.Ifthegeophysicaltestingisdoneasafirstphaseintheexplorationprogram,itcanalsobeusedtohelpdevelopthedetailedplanforsecondphaseexploration.Asaminimum,thesubsurfaceexplorationandtestingprogramshouldobtaininformationtoanalyzefoundationstabilityandsettlementwithrespectto:

Geologicalformation(s) Locationandthicknessofsoilandrockunits Engineeringpropertiesofsoilandrockunits,suchasunitweight,shearstrengthandcompressibility Groundwaterconditions



Groundsurfacetopography Localconsiderations,(e.g.,liquefiable,expansiveordispersivesoildeposits,undergroundvoidsfrom

solutionweatheringorminingactivity,orslopeinstabilitypotential)

Inareasunderlainbyheterogeneoussoildepositsand/orrockformations,itwillprobablybenecessarytoperformmoreinvestigationtocapturevariationsinsoiland/orrocktypeandtoassessconsistencyacrossthesitearea.Inalaterallyhomogeneousarea,drillingoradvancingalargenumberofboringsmayberedundant,sinceeachsampletestedwouldexhibitsimilarengineeringproperties.Inallcases,itisnecessarytounderstandhowthedesignandconstructionofthegeotechnicalfeaturewillaffectthesoiland/orrockmassinordertooptimizetheexploration.Thefollowingminimumguidelinesforfrequencyanddepthofexplorationshallbeused.Additionalexplorationmayberequireddependingonthevariabilityinsiteconditions,wall/slopegeometry,wall/slopetype,andtheconsequencesshouldafailureoccur.

15.3.4.1 Exploration Type, Depth, and SpacingGenerally,walls10feetorlessinheight,constructedoveraveragetogoodsoilconditions (e.g.,non-liquefiable,mediumdensetoverydensesand,siltorgravel,withnosignsofpreviousinstability)willrequireonlyabasiclevelofsiteinvestigation.Ageologicsitereconnaissance(seeWSDOT GDM Chapter 2),combinedwithwidelyspacedtestpits,handholes,orafewshallowboringstoverifyfieldobservationsandtheanticipatedsitegeologymaybesufficient,especiallyifthegeologyoftheareaiswellknown,orifthereissomepriorexperienceinthearea.

Thegeotechnicaldesignershouldinvestigatetoadepthbelowbottomofwallorreinforcedslopeatleasttoadepthwherestressincreaseduetoestimatedfoundationloadislessthan10%oftheexistingeffectiveoverburdenstressandbetween1and2timestheexposedheightofthewallorslope.Explorationdepthshouldbegreatenoughtofullypenetratesofthighlycompressiblesoils(e.g.peat,organicsilt,softfinegrainedsoils)intocompetentmaterialofsuitablebearingcapacity(e.g.,stifftohardcohesivesoil,compactdensecohesionlesssoil,orbedrock).Handholesandtestpitsshouldbeusedonlywheremediumdensetodensegranularsoilconditionsareexpectedtobeencounteredwithinlimitsthatcanbereasonablyexploredusingthesemethods,approximately10feetforhandholesand15feetfortestpits,andthatbasedonthesitegeologythereislittleriskofanunstablesoftorweaklayerbeingpresentthatcouldaffectwallstability.

Forretainingwallsandreinforcedslopeslessthan100feetinlength,theexplorationshouldoccurapproximatelymidpointalongthealignmentorwherethemaximumheightoccurs.Explorationsshouldbecompletedonthealignmentofthewallfaceorapproximatelymidpointalongthereinforcedslope,i.e.wheretheheightis0.5H.Additionalboringstoinvestigatethetoeslopeforwallsorthetoecatchforreinforcedslopesmayberequiredtoassessoverallstabilityissues.

Forretainingwallsandslopesmorethan100feetinlength,explorationpointsshouldbespacednomorethan500feetinuniform,densesoilconditionsandshouldbespacedat100to200ftintypicalsoilconditions.Evencloserspacingshouldbeusedinhighlyvariableandpotentiallyunstablesoilconditions.Wherepossible,locateatleastoneboringwherethemaximumheightoccurs.Explorationsshouldbecompletedonthealignmentofthewallfaceorapproximatelymidpointalongthereinforcedslope,i.e.wheretheheightis0.5H.Additionalboringstoinvestigatethetoeslopeforwallsorthetoecatchforreinforcedslopesmayberequiredtoassessoverallstabilityissues.



Akeytotheestablishmentofexplorationfrequencyforwallsisthepotentialforthesubsurfaceconditionstoimpacttheconstructionofthewall,theconstructioncontractingeneral,andthelong-termperformanceofthefinishedproject.Theexplorationprogramshouldbedevelopedandconductedinamannerthatthesepotentialproblems,intermsofcost,time,andperformance,arereducedtoanacceptablelevel.Theboringfrequencydescribedabovemayneedtobeadjustedbythegeotechnicaldesignertoaddresstheriskofsuchproblemsforthespecificproject.

15.3.4.2 Walls and Slopes Requiring Additional Exploration 15.3.4.2.1 SoilNailWallsSoilnailwallsshouldhaveadditionalgeotechnicalboringscompletedtoexplorethesoilconditionswithinthesoilnailzone.Theadditionalexplorationpointsshallbeatadistanceof1.0to1.5timestheheightofthewallbehindthewalltoinvestigatethesoilsinthenailzone.Boringsshouldbespacednomorethan500feetinuniform,densesoilconditionsandshouldbespacedat100to200ftintypicalsoilconditions.Evencloserspacingshouldbeusedinhighlyvariableandpotentiallyunstablesoilconditions.Thedepthoftheboringsshallbesufficienttoexplorethefulldepthofsoilswherenailsarelikelytobeinstalled,anddeepenoughtoaddressoverallstabilityissues.

Inaddition,eachsoilnailwallshouldhaveatleastonetestpitexcavatedtoevaluatestand-uptimeoftheexcavationface.Thetestpitshallbecompletedoutsidethenailpattern,butascloseaspracticaltothewallfacetoinvestigatethestand-uptimeofthesoilsthatwillbeexposedatthewallfaceduringconstruction.Thetestpitshallremainopenatleast24hoursandshallbemonitoredforsloughing,caving,andgroundwaterseepage.Atestpitlogshallbepreparedandphotographsshouldbetakenimmediatelyafterexcavationandat24hours.Ifvariablesoilconditionsarepresentalongthewallface,atestpitineachsoiltypeshouldbecompleted.Thedepthofthetestpitsshouldbeatleasttwicetheverticalnailspacingandthelengthalongthetrenchbottomshouldbeatleastoneandahalftimestheexcavationdepthtominimizesoil-archingeffects.Forexample,awallwithaverticalnailspacingof 4feetwouldhaveatestpit8feetdeepandatleast12feetinlengthatthebottomofthepit.

15.3.4.2.2WallswithGroundAnchorsorDeadmenAnchorsWallswithgroundanchorsordeadmananchorsshouldhaveadditionalgeotechnicalboringscompletedtoexplorethesoilconditionswithintheanchor/deadmanzone.Theseadditionalboringsshouldbespacednomorethan500feetinuniform,densesoilconditionsandshouldbespacedat100to200ftintypicalsoilconditions.Evencloserspacingshouldbeusedinhighlyvariableandpotentiallyunstablesoilconditions.Theboringsshouldbecompletedoutsidetheno-loadzoneofthewallinthebondzoneoftheanchorsoratthedeadmanlocations.Thedepthoftheboringsshallbesufficienttoexplorethefulldepthofsoilswhereanchorsordeadmenarelikelytobeinstalled,anddeepenoughtoaddressoverallstabilityissues.

15.3.4.2.3WallorSlopeswithSteepBackSlopesorSteepToeSlopesWallsorslopesthathaveabackslopesortoeslopesthatexceed10feetinslopelengthandthataresteeperthan2H:1Vshouldhaveatleastonehandhole,testpit,orgeotechnicalboringinthebackslopeortoeslopetodefinestratigraphyforoverallstabilityanalysisandevaluatebearingresistance.Theexplorationshouldbedeepenoughtoaddressoverallstabilityissues.Handholesandtestpitsshouldbeusedonlywheremediumdensetodensegranularsoilconditionsareexpectedtobeencounteredwithinlimitsthatcanbereasonablyexploredusingthesemethods,approximately10feetforhandholesand 20feetfortestpits.



15.3.5 Field, Laboratory, and Geophysical Testing for Abutments, Retaining Walls, and Reinforced Slopes Thepurposeoffieldandlaboratorytestingistoprovidethebasicdatawithwhichtoclassifysoilsandtoestimatetheirengineeringpropertiesfordesign.Oftenforabutments,retainingwalls,andreinforcedslopes,thebackfillmaterialsourcesarenotknownoridentifiedduringthedesignprocess.Forexample,mechanicallystabilizedearthwallsarecommonlyconstructedofbackfillmaterialthatisprovidedbytheContractorduringconstruction.Duringdesign,thematerialsourceisnotknownandhencematerialscannotbetested.Inthiscase,itisnecessarytodesignusingcommonlyacceptedvaluesforregionallyavailablematerialsandensurethatthecontractwillrequiretheuseofmaterialsmeetingorexceedingtheseassumedproperties.

Forabutments,thecollectionofsoilsamplesandfieldtestingshallbeinaccordancewithWSDOT GDM Chapters 2, 5, and 8.

Forretainingwallsandreinforcedslopes,thecollectionofsoilsamplesandfieldtestingarecloselyrelated. WSDOT GDM Chapter 5 providestheminimumrequirementsforfrequencyoffieldteststhataretobeperformedinanexplorationpoint.Asaminimum,thefollowingfieldtestsshallbeperformedandsoilsamplesshallbecollected:

Ingeotechnicalborings,soilsamplesshallbetakenduringtheStandardPenetrationTest(SPT).Finegrainedsoilsorpeatshallbesampledwith3-inchShelbytubesorWSDOTUndisturbedSamplersifthesoilsaretoostifftopush3-inchShelbytubes.AllsamplesingeotechnicalboringsshallbeinaccordancewithWSDOT GDM Chapters 2 and 3.

Inhandholes,sacksoilsamplesshallbetakenofeachsoiltypeencountered,andWSDOTPortablePenetrometertestsshallbetakeninlieuofSPTtests.Themaximumverticalspacingbetweenportablepenetrometertestsshouldbe5feet.

Intestpits,sacksoilsamplesshallbetakenfromthebucketoftheexcavator,orfromthespoilpileforeachsoiltypeencounteredoncethesoilisremovedfromthepit.WSDOTPortablePenetrometertestsmaybetakeninthetestpit.However,nopersonshallenteratestpittosampleorperformportablepenetrometertestsunlessthereisaprotectivesysteminplaceinaccordancewithWAC296-155-657.

Insoftsoils,CPTtestsorinsituvanesheartestsmaybecompletedtoinvestigatesoilstratigraphy,shearstrength,anddrainagecharacteristics.

Allsoilsamplesobtainedshallbereviewedbyageotechnicalengineerorengineeringgeologist.Thegeotechnicaldesignershallgroupthesamplesintostratigraphicunitsbasedonconsistency,color,moisturecontent,engineeringproperties,anddepositionalenvironment.AtleastonesamplefromeachstratigraphicunitshouldbetestedinthelaboratoryforGrainSizeDistribution,MoistureContent,andAtterbergLimits(finegrainedsoilsonly).Additionaltests,suchasLossonIgnition,pH,Resistivity,Sand Equivalent, or Hydrometer may be performed.



Wallsthatwillbeconstructedoncompressibleorfinegrainedsoilsshouldhaveundisturbedsoilsamplesavailableforlaboratorytesting,e.g.shelbytubesorWSDOTundisturbedsamples.ConsolidationtestsandUnconsolidatedUndrained(UU)triaxialtestsshouldbeperformedonfinegrainedorcompressiblesoilunits.AdditionaltestssuchasConsolidatedUndrained(CU),DirectShear,orLabVaneShearmaybeperformedtoestimateshearstrengthparametersandcompressibilitycharacteristicsofthesoils.

Geophysicaltestingmaybeusedforestablishingstratificationofthesubsurfacematerials,theprofileofthetopofbedrock,depthtogroundwater,limitsoftypesofsoildeposits,thepresenceofvoids,anomalousdeposits,buriedpipes,anddepthsofexistingfoundations.DatafromGeophysicaltestingshallalwaysbecorrelatedwithinformationfromdirectmethodsofexploration,suchasSPT,CPT,etc.

15.3.6 GroundwaterOneoftheprincipalgoalsofagoodfieldreconnaissanceandfieldexplorationistoaccuratelycharacterizethegroundwaterintheprojectarea.Groundwateraffectsthedesign,performance,andconstructabilityofprojectelements.Installationofpiezometer(s)andmonitoringisusuallynecessarytodefinegroundwaterelevations.GroundwatermeasurementsshallbeconductedinaccordancewithWSDOT GDM Chapter 2,andshallbeassessedforeachwall.Ingeneral,thiswillrequireatleastonegroundwatermeasurementpointforeachwall.Ifgroundwaterhasthepotentialtoaffectwallperformanceortorequirespecialmeasurestoaddressdrainagetobeimplemented,morethanonemeasurementpointperwallwillberequired.

15.4 GeneralDesignRequirements15.4.1 Design MethodsTheAASHTOLRFDBridgeDesignSpecificationsshallbeusedforallabutmentsandretainingwallsaddressedtherein.Thewallsshallbedesignedtoaddressallapplicablelimitstates(strength,service,andextremeevent).Rockwalls,reinforcedslopes,andsoilnailwallsarenotspecificallyaddressedintheAASHTOspecifications,andshallbedesignedinaccordancewiththismanual.ManyoftheFHWAmanualsusedasWSDOTdesignreferenceswerenotdevelopedforLRFDdesign.Forthosewalltypes(andincludingreinforcedslopes)forwhichLRFDproceduresarenotavailable,allowablestressdesignproceduresincludedinthismanual,eitherinfullorbyreference,shallbeused,againaddressingallapplicablelimitstates.

TheloadandresistancefactorsprovidedintheAASHTOLRFDSpecificationshavebeendevelopedinconsiderationoftheinherentuncertaintyandbiasofthespecifieddesignmethodsandmaterialproperties,andthelevelofsafetyusedtosuccessfullyconstructthousandsofwallsovermanyyears.Theseloadandresistancefactorsshallonlybeappliedtothedesignmethodsandmaterialresistanceestimationmethodsforwhichtheyareintended,ifanoptionisprovidedinthismanualortheAASHTOLRFDspecificationstousemethodsotherthanthosespecifiedhereinorintheAASHTOLRFDspecifications.Forestimationofsoilreinforcementpullout,theresistancefactorsprovidedaretobeusedonlyforthedefaultpulloutmethodsprovidedintheAASHTOLRFDspecifications.Ifwallsystemspecificpulloutresistanceestimationmethodsareused,resistancefactorsshallbedevelopedstatisticallyusingreliabilitytheorytoproduce a probability of failure Pfofapproximately1in100orsmaller.Notethatinsomecases,Section11oftheAASHTOLRFDBridgeDesignSpecificationsreferstoAASHTOLRFDSection10forwallfoundationdesignandtheresistancefactorsforfoundationdesign.Insuchcases,thedesignmethodologyandresistancefactorsprovidedintheWSDOT GDM Chapter 8shallbeusedinsteadoftheresistancefactorsinAASHTOLRFDSection10.



ItisrecognizedthatmanyoftheproprietarywallsuppliershavenotfullyimplementedtheLRFDapproachforthedesignoftheirwallsystem(s).TheapproveddetailsforthecurrentlypreapprovedproprietarywallsystemshavebeendevelopedinaccordancewiththeAASHTOStandardSpecificationsforHighwayBridges(2002).WSDOTwillallowagraceperiodforthewallsystemspreapprovedonorbeforeDecember1,2004,andhaveremainedinapprovedstatusuntilthepresent,regardingtheimplementationoftheLRFDapproach.Inthosecases,theAASHTOStandardSpecificationsforHighwayBridges(2002),asmodifiedintheWSDOT GDM,maybeusedforthedesignofthosesystemsuntilsuchtimethatWSDOTdecidestoendthegraceperiod.

Forwallswithatrafficbarrier,designofthetrafficbarrierandthedistributionoftheappliedimpactloadtothewalltopshallbeasdescribedintheAASHTOStandardSpecificationsforHighwayBridges(2002),Article5.8.12.2,forbothAASHTOStandardSpecificationwalldesignsandAASHTOLRFDSpecificationdesigns.

15.4.2 Special RequirementsAllwallsshallmeettherequirementsintheStateDesignManualforlayoutandgeometry.AllwallsshallbedesignedandconstructedinaccordancewiththeStandardSpecifications,GeneralSpecialProvisions,andStandardPlans.Specificdesignrequirementsfortieredwalls,back-to-backwalls,andMSEwallsupportedabutmentsareprovidedintheAASHTOLRFDBridgeDesignSpecifications(forpreapprovedproprietarywallsystems,alternativelyintheAASHTO Standard Specifications for Highway Bridges, 2002),andbyreferenceinthosedesignspecificationsElias, et al. (2001).

15.4.2.1 Tiered WallsWallsthatretainotherwallsorhavewallsassurchargesrequirespecialdesigntoaccountforthesurchargeloadsfromtheupperwall.Proprietarywallsystemsmaybeusedforthelowerwall,butproprietarywallsshallnotbeconsideredpreapprovedinthiscase.Chapter1130oftheWSDOTDesignManualdiscussestherequirementsforutilizingnon-preapprovedproprietarywallsonWSDOTprojects.Iftheupperwallisproprietary,apreapprovedsystemmaybeusedprovideditmeetstherequirementsforpreapprovalanddoesnotcontainsignificantstructuresorsurchargeswithinthewallreinforcing.

15.4.2.2 Back-to-Back WallsTheface-to-facedimensionforback-to-backsheetpilewallsusedasbulkheadsforwaterfrontstructuresmustexceedthemaximumexposedheightofthewalls.Bulkheadwallsmaybecrossbracedortiedtogetherprovidedthetierodsandconnectionsaredesignedtocarrytwicetheappliedloads.

ThefacetofacedimensionforbacktobackMechanicallyStabilizedEarth(MSE)wallsshallbe1.1timestheaverageheightoftheMSEwallsorgreater.Back-to-backMSEwallswithawidth/heightratiooflessthan1.1shallnotbeusedunlessapprovedbytheStateGeotechnicalEngineerandtheBridgeDesignEngineer.Themaximumheightforback-to-backMSEwallinstallationsis30feet.Thesoilreinforcementforback-to-backMSEwallsmaybeconnectedtobothfaces,i.e.,continuousfromonewalltotheother,providedthereinforcingisdesignedfordoubletheloading.Reinforcementmayoverlap,providedthereinforcementfromonewalldoesnotcontactthereinforcementfromtheotherwall.Reinforcementoverlapsofmorethan3feetaregenerallynotdesirableduetotheincreasedcostofmaterials.Preapprovedproprietarywallsystemsmaybeusedforback-to-backMSEwallsprovidedtheymeettheheight,height/widthratioandoverlaprequirementsspecifiedherein.



15.4.2.3 Walls on SlopesStandardPlanwallsfoundedonslopesshallmeettherequirementsintheStandardPlans.Allotherwallsshallhaveanearhorizontalbenchatthewallfaceatleast4feetwidetoprovideaccessformaintenance.BearingresistanceforfootingsinslopesandoverallstabilityrequirementsintheAASHTOLRFDBridgeDesignSpecificationsshallbemet(includingproprietarywallsdesignedusingtheAASHTOStandardSpecificationsforHighwayBridges,2002).

15.4.2.4 MSE Wall Supported AbutmentsMSEwallsdirectlysupportingspreadfootingbridgeabutmentsshallbe25 feet orlessintotalheight.Abutmentspreadfootingserviceloadsshouldnotexceed3.0TSF.ProprietaryMSEwallssupportingabutmentsshallnotbeconsideredpreapproved,andshallnotbeusedbeyondthelimitsdescribedhereinunlessapprovedbytheStateGeotechnicalEngineerandtheBridgeDesignEngineer.Thefrontedgeoftheabutmentfootingshallbe2feetormorefromthebackoftheMSEfacingunits.Thereshallbeatleast5feetverticalclearancebetweentheMSEfacingunitsandthebottomofthesuperstructure,and5feethorizontalclearancebetweenthebackoftheMSEfacingunitsandfaceoftheabutmentwalltoprovideaccessforbridgeinspection.Fallprotectionshallbeinstalledasnecessary.TheseMSEabutmentcriteriaarealsoapplicabletoproprietarywallsdesignedusingtheAASHTOStandardSpecificationsforHighwayBridges(2002).

ThebearingresistanceforthefootingsupportedbytheMSEwallisafunctionofthesoilreinforcementdensityinadditiontotheshearstrengthofthesoil.IfdesigningthewallusingLRFD,twocasesshouldbeevaluatedtosizethefootingforbearingresistanceforthestrengthlimitstate,astwosetsofloadfactorsareapplicable:

Theloadfactorsapplicabletothestructureloadsappliedtothefooting,suchasDC,DW,EH,LL,etc.

Theloadfactorapplicabletothedistributionofsurchargeloadsthroughthesoil,ES.

WhenESisusedtofactortheloadappliedtothesoiltoevaluatebearing,thestructureloadsandliveloadappliedtothefootingshouldbeunfactored.WhenESisnotusedtofactortheloadappliedtothesoiltoevaluatebearing,thestructureloadsandliveloadappliedtothefootingshouldbefactoredusingDC,DW,EH,LL,etc.Thewallshouldbedesignedforbothcases,andthecasethatresultsinthegreatestamountofsoilreinforcementshouldbeusedforthefinalstrengthlimitstatedesign.

15.4.2.5 Minimum EmbedmentAllwallsandabutmentsshouldmeettheminimumembedmentcriteriainAASHTO.ThefinalembedmentdepthrequiredshallbebasedongeotechnicalbearingandstabilityrequirementsprovidedintheAASHTOLRFDspecifications,asdeterminedbythegeotechnicaldesigner.Wallsthathaveaslopinggroundlineatthefaceofwallmayneedtohaveaslopingorsteppedfoundationtooptimizethewallembedment.Slopingfoundations(i.e.,notstepped)shallbe4H:1Vorflatter.Steppedfoundationsshallbe1.5H:1Vorflatterdeterminedbyalinethroughthecornersofthesteps.Themaximumfeasibleslopeofsteppedfoundationsforwallsiscontrolledbythemaximumacceptablestableslopeforthesoilinwhichthewallfootingisplaced.ConcretelevelingpadsconstructedforMSEwallsshallbeslopedat4H:1Vorflatterorsteppedat1.5H:1Vorflatterdeterminedbyalinethroughthecornersofthesteps.AsMSEwallfacingunitsaretypicallyrectangularshapes,steppedlevelingpadsarepreferred.TheseembedmentcriteriaarealsoapplicabletoproprietarywallsdesignedusingtheAASHTOStandardSpecificationsforHighwayBridges(2002).



15.4.2.6 Serviceability RequirementsWallsshallbedesignedtostructurallywithstandtheeffectsoftotalanddifferentialsettlementestimatedfortheprojectsite,bothlongitudinallyandincross-section,asprescribedintheAASHTOLRFDSpecifications.Inadditiontotherequirementsforserviceabilityprovidedabove,thefollowingcriteria(Tables 15-2, 15-3, and 15-4)shallbeusedtoestablishacceptablesettlementcriteria(includingproprietarywallsdesignedusingtheAASHTOStandardSpecificationsforHighwayBridges,2002):

TotalSettlement DifferentialSettlementOver100ft Action

H1in H1000.75in DesignandConstruct1in2in ObtainApproval1priortoproceedingwithdesignandConstruction

1ApprovalofWSDOTStateGeotechnicalEngineerandWSDOTBridgeDesignEngineerrequired.

Table15-2 SettlementcriteriaforReinforcedConcreteWalls,NongravityCantileverWalls,Anchored/BracedWalls,andMSEWallswithFullHeightPrecastConcretePanels

(soilisplacedirectlyagainstpanel).


H2in H1001.5in DesignandConstruct2in3in ObtainApproval1priortoproceedingwithdesignandConstruction


Table15-3 SettlementcriteriaforMSEWallswithModular(segmental)BlockFacings,PrefabricatedModularWalls,andRockWalls.


H4in H503in DesignandConstruct4in9in ObtainApproval1priortoproceedingwithdesignandConstruction


Table15-4 SettlementcriteriaforMSEWallswithFlexibleFacingsandReinforcedSlopes.

ForMSEwallswithprecastpanelfacingsupto75ft2inarea,limitingdifferentialsettlementsshallbeasdefinedintheAASHTOLRFDSpecifications,ArticleC11.10.4.1.

Notethatmorestringenttolerancesmaybenecessarytomeetaestheticrequirementsforthewalls.



15.4.2.7 Active, Passive, At-rest Earth PressuresThegeotechnicaldesignershallassesssoilconditionsandshalldevelopearthpressurediagramsforallwallsexceptstandardplanwallsinaccordancewiththeAASHTOLRFDBridgeDesignSpecifications.EarthpressuresmaybebasedoneitherCoulomborRankinetheories.Thetypeofearthpressureusedfordesigndependsontheabilityofthewalltoyieldinresponsetotheearthloads.Forwallsthatfreetotranslateorrotate(i.e.,flexiblewalls),activepressuresshallbeusedintheretainedsoil.Flexiblewallsarefurtherdefinedasbeingabletodisplacelaterallyatleast0.001H,whereHistheheightofthewall.Standardconcretewalls,MSEwalls,soilnailwalls,soldierpilewallsandanchoredwallsaregenerallyconsideredasflexibleretainingwalls.Non-yieldingwallsshalluseat-restearthpressureparameters.Nonyieldingwallsinclude,forexample,integralabutmentwalls,wallcorners,cutandcovertunnelwalls,andbracedwalls(i.e.,wallsthatarecross-bracedtoanotherwallorstructure.Wherebridgewingandcurtainwallsjointhebridgeabutment,atrestearthpressuresshouldbeused.Atdistancesawayfromthebridgeabutmentequaltoorgreaterthantheheightoftheabutmentwall,activeearthpressuresmaybeused.Thisassumesthatatsuchdistancesawayfromthebridgeabutment,thewingorcurtainwallcandeflectenoughtoallowactiveconditionstodevelop.

Ifexternalbracingisused,activepressuremaybeusedfordesign.Forwallsusedtostabilizelandslides,theappliedearthpressureactingonthewallshallbeestimatedfromlimitequilibriumstabilityanalysisoftheslideandwall(externalandglobalstabilityonly).Theearthpressureforceshallbetheforcenecessarytoachievestabilityintheslope,whichmayexceedat-restorpassivepressure.

15.4.2.8 Surcharge LoadsArticle3.11.6intheAASHTOLRFDBridgeDesignSpecificationsshallbeusedforsurchargeloadsactingonallretainingwallsandabutmentsforwallsinwhichthegroundsurfacebehindthewallis4H:IVorflatter,thewallshallbedesignedforthepossiblepresenceofconstructionequipmentloadsimmediatelybehindthewall.Theseconstructionloadsshallbetakenintoaccountbyapplyinga250psfliveloadsurchargetothegroundsurfaceimmediatelybehindthewall.Sincethisisatemporaryconstructionload,seismicloadsshouldnotbeconsideredforthisloadcase.

15.4.2.9 Seismic Earth PressuresForallwallsandabutments,theMononobe-OkabemethoddescribedintheAASHTOLRFDBridgeDesignSpecifications,Chapter11andAppendixA11.1.1.1,shallbeused.Inaddition,forthisapproachitisassumedthatthewallbackfilliscompletelydrainedandcohesionless(i.e.notsusceptibletoliquefaction).

Wallsandabutmentsthatarefreetotranslateormoveduringaseismicevent(seeSection 15.4.2.6)mayuseareducedhorizontalaccelerationkh of approximately one-halfpeakgroundaccelerationorasspecificallycalculatedinArticle11.6.5oftheAASHTOLRFDBridgeDesignSpecificationsintheMononobe-Okabemethod.Verticalacceleration,kv,shouldbesetequalto0.

Wallsandabutmentsthatarenotfreetotranslateormoveduringaseismicevent(seeSection 15.4.2.6)shalluseahorizontalaccelerationof1.5timespeakgroundacceleration.Verticalaccelerationshallbesetequal to 0.



ThecurrentAASHTOspecificationsarenotconsistentregardingthelocationoftheresultant,noraretheyconsistentregardingtheseparationofthestaticearthpressurefromtheseismicearthpressure(i.e.,theuseofKaetorepresenttheseismicportionoftheearthpressureversustheuseofKaetorepresentthetotaloftheseismicandstaticearthpressure).Untilthisissueisresolved,thefollowingpolicyshallbeimplementedregardingseismicearthpressurecalculation:

TheseismiccomponentoftheMononobe-OkabeearthpressuremaybeseparatedfromthestaticearthpressureactingonthewallasshowninArticle11.10.7.1intheAASHTOLRFDBridgeDesignSpecifications.Ifthisisdone,theseismiccomponent,Kae,shallbecalculatedasKaeKaforwallsthatarefreetomoveanddevelopactiveearthpressureconditions,andasKaeK0forwallsthatarenotfreetomove(i.e.,atrestearthpressureconditionsprevail,andKaeiscalculatedusingahorizontalaccelerationof1.5timesthepeakgroundacceleration).Notethatinthiscase,tocompletetheseismicdesignofthewall,thestaticearthpressureresultingfromKaorK0 must be added to the seismiccomponentoftheearthpressureresultingfromKaetoobtainthetotalearthpressureactingintheextremeeventlimitstate.TheloadfactorforEQinSection3oftheAASHTOLRFDBridgeDesignSpecifications(i.e.,aloadfactorof1.0)shallbeappliedtothestaticandseismicearth pressureloads,sinceinMononobe-Okabeearthpressureanalysis,atotalstaticplusseismicearthpressureiscalculatedasoneforceinitially,andthenseparatedintothestaticandseismiccomponentsasasecondstep.

TheresultantforceoftheMononobe-Okabeearthpressuredistribution,asrepresentedbyKaeshouldbeappliedat0.6Hfromthebottomofthepressuredistribution.Notethatthedistributionisaninvertedtrapezoidiftheresultantisappliedat0.6H,withthepressureatthetopofthedistributionequalto0.8KaeH,andthepressureatthebottomequalto0.2KaeH.

Iftheseismicearthpressureforceiscalculatedanddistributedasasingleforceasspecifiedin AppendixA11.1.1.1oftheAASHTOLRFDBridgeDesignSpecifications,thecombinedearth pressureforceshallbeappliedat0.5Hfromthebottomofthepressuredistribution,resultingina uniformpressuredistributioninwhichthepressureisequalto0.5KaeH.Notethatsincethis uniformpressuredistributionincludesboththestaticandseismiccomponentoflateralearthpressure,thisuniformearthpressuremust not be addedtotheearthpressureresultingfromKaorK0.

Forallwalls,thepressuredistributionshouldbeappliedfromthebottomofwalltothetopofwall exceptcantileverwalls,anchoredwalls,orbracedwalls.Forthesewalls,thepressureshouldbe appliedfromthetopofwalltotheelevationoffinishedgroundlineatthefaceofwall.

TheMononobe-Okabeseismicearthpressuretheorywasdevelopedforasinglelayercohesionlesssoilwithnowaterpresent.Formostgravitywalls,thisassumptionisapplicableinmostcases.However,forcutwallssuchasanchoredwallsornon-gravitycantileverwalls,itispossibleandevenlikelythattheseassumptionsmaynotbeapplicable.Insuchcaseswheretheseassumptionsarenotfullyapplicable,aweightedaverage(weightedbasedonthethicknessofeachlayer)ofthesoilproperties(e.g.,effectivestress and )shouldbeusedtocalculateKae.Onlythesoilabovethedredgelineorfinishedgradeinfrontofthewallshouldbeincludedintheweightedaverage.Ifwaterbehindthewallcannotbefullydrained,thelateralpressureduetothedifferenceinheadmustbeaddedtothepressureresultingfromKae toobtainthetotallateralforceactingintheseismiclimitstate(noteKaeincludesthetotalofseismicandactiveearthpressure,asdescribedpreviously).Ifcohesivesoilsarepresentbehindthewall,theresidualdrainedfrictionangleratherthanthepeakfrictionangle(seeWSDOT GDM Chapter 5)shouldbeusedtodeterminetheseismiclateralearthpressure.

Notealsothattheslopeoftheactivefailureplaneflattensastheearthquakeaccelerationincreases.Foranchoredwalls,theanchorsshouldbelocatedbehindtheactivefailurewedge.ThemethodologyprovidedinFHWAGeotechnicalEngineeringCircularNo.4(Sabatini, et al., 1999)shouldbeusedtolocatetheactivefailureplaneforthepurposeofanchoredzonelocationforanchoredwalls.



SincetheloadfactorusedfortheseismiclateralearthpressureforEQiscurrently1.0,toobtainthesamelevelofsafetyforslidingandbearingobtainedfromtheAASHTOStandardSpecificationdesignrequirements,aresistancefactorofslightlylessthan1.0isrequired.Forslidingandbearingresistanceduringseismicloading,aresistancefactorof0.9shouldbeused.

TheseismicdesigncriteriaprovidedinthissectionarealsoapplicabletoproprietarywallsdesignedusingtheAASHTOStandardSpecificationsforHighwayBridges(2002).

15.4.2.10 LiquefactionUnderextremeeventloading,liquefactionandlateralspreadingmayoccur.Thegeotechnicaldesignershallassessliquefactionandlateralspreadingforthesiteandidentifythesegeologichazards.DesigntoassessandtomitigatethesegeologichazardsshallbeconductedinaccordancewiththeprovisionsinWSDOT GDM Chapter 6.

15.4.2.11 Overall StabilityAllretainingwallsandreinforcedslopesshallhavearesistancefactorforoverallstabilityof0.75(i.e.,asafetyfactorof1.3).Allabutmentsandthoseretainingwallsandreinforcedslopesdeemedcriticalshallhavearesistancefactorof0.65(i.e.,asafetyfactorof1.5).Criticalwallsandslopesarethosethatsupportimportantstructureslikebridgesandotherretainingwalls.Criticalwallsandslopeswouldalsobethosewhosefailurewouldresultinalifethreateningsafetyhazardforthepublic,orwhosefailureandsubsequentreplacementorrepairwouldbeanintolerablefinancialburdentothecitizensofWashingtonState.

StabilityshallbeassessedusinglimitingequilibriummethodsinaccordancewithWSDOT GDM Chapter 7.

15.4.2.12 Wall Drainage Drainageshouldbeprovidedforallwalls.Ininstanceswherewalldrainagecannotbeprovided,thehydrostaticpressurefromthewatershallbeincludedinthedesignofthewall.Ingeneral,walldrainageshallbeinaccordancewiththeStandardPlans,GeneralSpecialProvisions,andtheWSDOTDesignManual.Figure1130-2inthedesignmanualshallbeusedfordraindetailsanddrainplacementforallwallsnotcoveredbyWSDOTStandardPlanD-4exceptasfollows:

Gabionwallsandrockwallsaregenerallyconsideredpermeableanddonottypicallyrequirewalldrains,providedconstructiongeotextileisplacedagainstthenativesoilorfill.

Soilnailwallsshallusecompositedrainagematerialcenteredbetweeneachcolumnofnails.Thedrainagematerialshallbeconnectedtoweepholesusingadraingateorshallbewrappedaroundanunderdrain.

CantileverandAnchoredwallsystemsusinglaggingshallhavecompositedrainagematerialattachedtothelaggingfacepriortocastingthepermanentfacing.Wallswithoutfacingorwallsusingprecastpanelsarenotrequiredtousecompositedrainagematerialprovidedthewatercanpassthroughthelagging unhindered.



15.4.2.13 UtilitiesWallsthathaveormayhavefutureutilitiesinthebackfillshouldminimizetheuseofsoilreinforcement.MSE,soilnail,andanchoredwallscommonlyhaveconflictswithutilitiesandshouldnotbeusedwhenutilitiesmustremaininthereinforcedsoilzoneunlessthereisnootherwalloption.Utilitiesthatareencapsulatedbywallreinforcementmaynotbeaccessibleforreplacementormaintenance.Utilityagreementsshouldspecificallyaddressfutureaccessifwallreinforcingwillaffectaccess.

15.4.2.14 Guardrail and BarrierGuardrailandbarriershallmeettherequirementsoftheStateDesignManual,BridgeDesignManual,StandardPlans,andtheAASHTOLRFDBridgeDesignSpecifications.InnocaseshallguardrailbeplacedthroughMSEwallorreinforcedslopesoilreinforcementcloserthan3ftfromthebackofthewallfacingelements.Furthermore,theguardrailpostsshallbeinstalledthroughthesoilreinforcementinamannerthatpreventsrippinganddistortionofthesoilreinforcement,andthesoilreinforcementshallbedesignedtoaccountforthereducedcross-sectionresultingfromtheguardrailpostholes.

15.5 SpecificDesignRequirements15.5.1 Abutments and Standard Plan WallsAbutmentfoundationsshallbedesignedinaccordancewithWSDOT GDM Chapter 8.Abutmentwalls,wingwalls,andcurtainwallsshallbedesignedinaccordancewithAASHTOLRFDBridgeDesignSpecifications.Abutmentsthatarebackfilledpriortoconstructingthesuperstructureshallbedesignedusingactiveearthpressures.Activeearthpressuresshallbeusedforabutmentsthatarebackfilledafterconstructionofthesuperstructure,iftheabutmentcanmovesufficientlytodevelopactivepressures.Iftheabutmentisrestrained,at-restearthpressureshallbeused.AbutmentsthatareUshapedorthathavecurtain/wingwallsshouldbedesignedtoresistat-restpressuresinthecorners,asthewallsareconstrained(seeWSDOT GDM Section 15.4.2.7).

Forstandardplanwalls,theinternalstabilitydesignandtheexternalstabilitydesignforoverturningandslidingstabilityhavealreadybeencompleted.Thegeotechnicaldesignershallassessoverallslopestability,soilbearingresistance,andsettlementforeachstandardplanwalllocation.SincetheseStandardPlanwallshavebeendesignedusingLoadFactorDesignpertheAASHTOStandardSpecificationsforHighwayBridges(2002),geotechnicalsafetyfactorsconsistentwiththeAASHTOStandardSpecificationsshallbeusedforStandardPlanwallsuntilsuchtimethattheyhavebeenupdatedtouseLRFD methodology.

15.5.2 Nongravity Cantilever and Anchored WallsWSDOTtypicallydoesnotutilizesheetpilewallsforpermanentapplications,exceptatWashingtonStateFerries(WSF)facilities.SheetpilewallsmaybeusedatWSFfacilitiesbutshallnotbeusedelsewherewithoutapprovaloftheWSDOTBridgeDesignEngineer.SheetpilewallsutilizedforshoringorcofferdamsshallbetheresponsibilityoftheContractorandshallbeapprovedonconstruction,unlesstheconstructioncontractspecialprovisionsorplansstateotherwise.

Permanentsoldierpilesforsoldierpileandanchoredwallsshouldbeinstalledindrilledholes.Impactorvibratorymethodsmaybeusedtoinstalltemporarysoldierpiles,butinstallationindrilledholesispreferred.



NongravityandAnchoredwallsshallbedesignedusingthelatesteditionoftheAASHTOLRFDBridgeDesignSpecifications.KeygeotechnicaldesignrequirementsforthesetypesofwallsarefoundinSections3and11oftheAASHTOLRFDspecifications.InsteadoftheresistancefactorforpassiveresistanceoftheverticalwallelementsprovidedintheAASHTOLRFDspecifications,aresistancefactorforpassiveresistanceof0.75shallbeused.

15.5.2.1 Nongravity Cantilever WallsTheexposedheightofnongravitycantileverwallsisgenerallycontrolledbyacceptabledeflectionsatthetopofwall.Ingoodsoils,cantileverwallsaregenerally12to15feetorlessinheight.Greaterexposedheightscanbeachievedwithincreasedsectionmodulusortheuseofsecant/tangentpiles.Nongravitycantileverwallsusingasinglerowofgroundanchorsordeadmenanchorsshallbeconsideredananchoredwall.

Ingeneral,thedrilledholeforthesoldierpilesfornongravitycantileverwallswillbefilledwitharelativelylowstrengthflowablematerialsuchascontrolleddensityfill(CDF),providedthatwaterisnotpresentinthedrilledhole.SinceCDFhasarelativelylowcementcontent,thecementitiousmaterialintheCDFhasatendencytowashoutwhenplacedthroughwater.IftheCDFbecomestooweakbecauseofthis,thedesignassumptionthatthefullwidthofthedrilledhole,ratherthanthewidthofthesoldierpilebyitself,governsthedevelopmentofthepassiveresistanceinfrontofthewallwillbecomeinvalid.Thepresenceofgroundwaterwillaffectthechoiceofmaterialspecifiedbythestructuraldesignertobackfillthesoldierpileholes,e.g.,CDFiftheholeisnotwet,orhigherstrengthconcretedesignedfortremieapplications.Therefore,itisimportantthatthegeotechnicaldesigneridentifythepotentialforgroundwaterinthedrilledholesduringdesign,asthegeotechnicalstabilityofanongravitycantileversoldierpilewallisgovernedbythepassiveresistanceavailableinfrontofthewall.

Ifthewallisbeingusedtostabilizeadeepseatedlandslide,ingeneral,itshouldbeassumedthatfullstrengthconcretewillbeusedtobackfillthesoldierpileholes,astheshearingresistanceoftheconcretewillbeusedtohelpresistthelateralforcescausedbythelandslide.

15.5.2.2 Anchored/Braced WallsAnchored/bracedwallsgenerallyconsistofaverticalstructuralelementssuchassoldierpilesordrilledshaftsandlateralanchorageelementsplacedbesideorthroughtheverticalstructuralelements.DesignofthesewallsshallbeinaccordancewiththeAASHTOLRFDBridgeDesignSpecifications.

Ingeneral,thedrilledholeforthesoldierpilesforanchored/bracedwallswillbefilledwitharelativelylowstrengthflowablematerialsuchascontrolleddensityfill(CDF).Foranchoredwalls,thepassiveresistanceinfrontofthewalltoeisnotascriticalforwallstabilityasisthecasefornongravitycantileverwalls.Foranchoredwalls,resistanceatthewalltoetopreventkickoutisprimarilyafunctionofthestructuralbendingresistanceofthesoldierpileitself.Therefore,itisnotascriticalthattheCDFmaintainitsfullshearstrengthduringandafterplacementiftheholeiswet.Foranchored/bracedwalls,theonlytimefullstrengthconcretewouldbeusedtofillthesoldierpileholesintheburiedportionofthewalliswhentheanchorsaresteeplydipping,resultinginrelativelyhighverticalloads,orforthecasewhenadditionalshearstrengthisneededtoresisthighlateralkickoutloadsresultingfromdeepseatedlandslides.Inthecaseofwallsusedtostabilizedeepseatedlandslides,thegeotechnicaldesignermustclearlyindicatetothestructuraldesignerwhetherornottheshearresistanceofthesoldierpileandcementitiousbackfillmaterial(i.e.,fullstrengthconcrete)mustbeconsideredaspartoftheresistanceneededtohelpstabilizethelandslide.



15.5.2.3 Permanent Ground AnchorsThegeotechnicaldesignershalldefinetheno-loadzoneforanchorsinaccordancewiththeAASHTOLRFDBridgeDesignSpecifications.Ifthegroundanchorsareinstalledthroughlandslidematerialormaterialthatcouldpotentiallybeunstable,thenoloadzoneshallincludetheentireunstablezoneasdefinedbytheactualorpotentialfailuresurfaceplus5ftminimum.Thecontractdocumentsshouldrequirethedrillholeinthenoloadzonetobebackfilledwithanon-structuralfiller.Contractorsmayrequesttofillthedrillholeinthenoloadzonewithgroutpriortotestingandacceptanceoftheanchor.Thisisusuallyacceptableprovidedbondbreakersarepresentonthestrands,theanchorunbondedlengthisincreasedby8feetminimum,andthegroutintheunbondedzoneisnotplacedbypressuregroutingmethods.

Thegeotechnicaldesignershalldeterminethefactoredanchorpulloutresistancethatcanbereasonablyusedinthestructuraldesigngiventhesoilconditions.ThegroundanchorsusedontheprojectsshallbedesignedbytheContractor.Compressionanchors(seeSabatini, et al., 1999)maybeused,butconventionalanchorsarepreferredbyWSDOT.

Thegeotechnicaldesignershallestimatethenominalanchorbondstress(n)forthesoilconditionsandcommonanchorgroutingmethods.AASHTOLRFDBridgeDesignSpecificationsandtheFHWApublicationslistedatthebeginningofthischapterprovideguidanceonacceptablevaluestouseforvarioustypesofsoilandrock.Thegeotechnicaldesignershallthenapplyaresistancefactortothenominalbondstresstodetermineafeasiblefactoredpulloutresistance(FPR)foranchorstobeusedinthewall.Ingeneral,a5-inchdiameterlowpressuregroutedanchorwithabondlengthof15to30feetshouldbeassumedwhenestimatingthefeasibleanchorresistance.FHWAresearchhasindicatedthatanchorbondlengthsgreaterthan40feetarenotfullyeffective.Anchorbondlengthsgreaterthan50feetshallbeapprovedbytheStateGeotechnicalEngineer.

Thestructuraldesignershallusethefactoredpulloutresistancetodeterminethenumberofanchorsrequiredtoresistthefactoredloads.ThestructuraldesignershallalsousethisvalueinthecontractdocumentsastherequiredanchorresistancethatContractorneedstoachieve.TheContractorwilldesigntheanchorbondzonetoprovidethespecifiedresistance.TheContractorwillberesponsiblefordeterminingtheactuallengthofthebondzone,holediameter,drillingmethods,andgroutingmethodusedfortheanchors.

Allgroundanchorsshallbeprooftested,exceptforanchorsthataresubjectedtoperformancetests.Aminimumof5percentofthewallsanchorsshallbeperformancetested.Forgroundanchorsinclays,orothersoilsthatareknowntobepotentiallyproblematic,especiallywithregardtocreep,atleastoneverificationtestshallbeperformedineachsoiltypewithintheanchorzone.PastWSDOTpracticehasbeentoperformverificationtestsattwotimesthedesignloadwithproofandperformancetestsdoneto1.5timesthedesignload.Nationalpracticehasbeentotestto1.33timesthedesignloadforproofandperformancetests.Historically,WSDOThasutilizedahighersafetyfactorinitsanchoredwalldesigns(FS=1.5)principallyduetopastperformancewithanchorsconstructedinSeattleClay.ForanchorsthatareinstalledinSeattleClay,othersimilarformations,orclaysingeneral,thelevelofsafetyobtainedinpastWSDOTpracticeshallcontinuetobeused(i.e.,FS=1.5).Foranchorsinothersoils(e.g.,sands,gravels,glacialtills,etc.),thelevelofsafetyobtainedwhenapplyingthenationalpractice(i.e.,FS=1.33)shouldbeused.



TheAASHTOLRFDBridgeDesignSpecificationsspecificallyaddressesanchortesting.However,tobeconsistentwithpreviousWSDOTpractice,verificationtests,ifconducted,shallbeperformedto1.5timesthefactoreddesignload(FDL)fortheanchor.Proofandperformancetestsshallbeperformedto1.15timesthefactoreddesignload(FDL)foranchorsinstalledinclays,andto1.00timesthefactoreddesignload(FDAL)foranchorsinothersoilsandrock.Thegeotechnicaldesignershouldmakethedecisionduringdesignastowhetherornotahighertestloadisrequiredforanchorsinaportionof,orallof,thewallduetothepresenceofclaysorotherproblematicsoils.Theseproof,performance,andverificationtestloadsassumethataloadfactor,EH,of1.35isappliedtotheapparentearthpressureusedtodesigntheanchoredwall.

Thefollowingshallbeusedforverificationtests:

Load HoldTimeAL 1Min.

0.25FDL 10Min.0.50FDL 10Min.0.75FDL 10Min.1.00FDL 10Min.1.15FDL 60Min.1.25FDL 10Min.1.50FDL 10Min.

AL 1Min.

AListhealignmentload.Thetestloadshallbeappliedinincrementsof25percentofthedesignload.Eachloadincrementshallbeheldforatleast10minutes.Measurementofanchormovementshallbeobtainedateachloadincrement.Theload-holdperiodshallstartassoonasthetestloadisappliedandtheanchormovement,withrespecttoafixedreference,shallbemeasuredandrecordedat1minute,2,3,4,5,6,10,15,20,25,30,45,and60minutes.

Thefollowingshallbeusedforprooftests,foranchorsinclayorothercreepsusceptibleorotherwiseproblematicsoilsorrock:


0.25FDL 1Min.0.50FDL 1Min.0.75FDL 1Min.1.00FDL 1Min.1.15FDL 10Min.

AL 1Min.



Thefollowingshallbeusedforprooftests,foranchorsinsands,gravels,glacialtills,rock,orothermaterialswherecreepisnotlikelytobeasignificantissue:


0.25FDL 1Min.0.50FDL 1Min.0.75FDL 1Min.1.00FDL 10Min.

AL 1Min.

Themaximumtestloadinaprooftestshallbeheldfortenminutes,andshallbemeasuredandrecordedat1minute,2,3,4,5,6,and10minutes.Iftheanchormovementbetweenoneminuteandtenminutesexceeds0.04inches,themaximumtestloadshallbeheldforanadditional50minutes.Iftheloadholdisextended,theanchormovementsshallberecordedat15,20,25,30,45,and60minutes.

Performancetestscycletheloadappliedtotheanchor.Betweenloadcycles,theanchorisreturnedtothealignmentload(AL)beforebeginningthenextloadcycle.Thefollowingshallbeusedforperformancetests:

Cycle1 Cycle2 Cycle3 Cycle4 Cycle5* Cycle6AL AL AL AL AL AL

0.25FDL 0.25FDL 0.25FDL 0.25FDL 0.25FDL Lock-off0.50FDL 0.50FDL 0.50FDL 0.50FDL

0.75FDL 0.75FDL 0.75FDL

1.00FDL 1.00FDL

1.15FDL

*Thefifthcycleshallbeconductediftheanchorisinstalledinclayorotherproblematicsoils.Otherwise,theloadholdisconductedat1.00FDLandthefifthcycleiseliminated.

Theloadshallberaisedfromoneincrementtoanotherimmediatelyafteradeflectionreading.Themaximumtestloadinaperformancetestshallbeheldfortenminutes.Iftheanchormovementbetweenoneminuteandtenminutesexceeds0.04inches,themaximumtestloadshallbeheldforanadditional50minutes.Iftheloadholdisextended,theanchormovementsshallberecordedat15,20,25,30,45,and60minutes.Afterthefinalloadhold,theanchorshallbeunstressedtothealignmentloadthenjackedtothelock-offload.

Thestructuraldesignershouldspecifythelock-offloadinthecontract.PastWSDOTpracticehasbeentolock-offat80%oftheanchordesignload.Becausethefactoreddesignloadfortheanchorishigherthanthedesignloadusedinpastpractice,lockingoffat80%wouldresultinhighertendonloads.Tomatchpreviouspractice,thelock-offloadforallpermanentgroundanchorsshallbe60%ofthefactoreddesignload for the anchor.



Sincethecontractordesignsandinstallstheanchor,thecontractdocumentsshouldrequirethefollowing:

1.Factoreddesignload(FDL)shallnotexceed60%ofthespecifiedminimumtensilestrength(SMTS)for the anchor.

2.Lockoffshallnotexceed70%ofthespecifiedminimumtensilestrengthfortheanchor.

3.Testloadsshallnotexceed80%ofthespecifiedminimumtensilestrengthfortheanchor.

4.Allanchorsshallbedoublecorrosionprotected(encapsulated).Epoxycoatedorbarestrandsshallnotbeusedunlessthewallistemporary.

5.Groundanchorinstallationangleshouldbe15to30degreesfromhorizontal,butmaybeassteepas45degreestoinstallanchorsincompetentmaterialsorbelowfailureplanes.

Thegeotechnicaldesignerandthestructuraldesignershoulddeveloptheconstructionplansandspecialprovisionstoensurethatthecontractorcomplieswiththeserequirements.

15.5.2.4 DeadmenThegeotechnicaldesignershalldevelopearthpressuresandpassiveresistancefordeadmeninaccordancewithAASHTOLRFDBridgeDesignSpecifications.DeadmenshallbelocatedinaccordancewithFigure20fromNAVFACDM-7.2,FoundationsandEarthStructures,May1982(reproducedbelowforconvenience in Figure 15-2).



Figure15-2 Deadmananchordesign(afterNAVFAC,1982).



15.5.3 Mechanically Stabilized Earth WallsPreapprovedwallsystemsshallbe33feetorlessintotalheight.Specificproprietarywallsystemsmayhavemorestringentheightlimitations.Greaterwallheightsmaybeused,butaspecialdesign(i.e.,notpreapproved)willberequired.WalldesignshallbeinaccordancewiththeAASHTOLRFDBridgeDesignSpecifications,exceptasnotedbelowregardingtheuseoftheK-StiffnessMethodforinternalstabilitydesign.Asnotedpreviously,WSDOTwillallowagraceperiodfortheproprietarywallsystemspreapprovedonorbeforeDecember1,2004,andthathaveremainedinapprovedstatusuntilthepresent,regardingtheimplementationoftheLRFDapproach.Inthosecases,theAASHTOStandardSpecificationsforHighwayBridges(2002),asmodifiedintheWSDOTGDM,maybeusedforthedesignofthosesystemsuntilsuchtimethatWSDOTdecidestoendthegraceperiod.

Forwallswithatrafficbarrier,designofthetrafficbarrierandthedistributionoftheappliedimpactloadtothewalltopshallbeasdescribedintheAASHTOStandardSpecificationsforHighwayBridges(2002),Article5.8.12.2,forbothAASHTOStandardSpecificationwalldesignsandAASHTOLRFDSpecificationdesigns.

15.5.3.1 Internal Stability Using K-Stiffness MethodTheK-StiffnessMethod,asdescribedbyAllen and Bathurst (2003),maybeusedasanalternativetotheSimplifiedMethodprovidedintheAASHTOLRFDBridgeDesignSpecifications(Sections3 and11)todesigntheinternalstabilityforwallsupto25ftinheightthatarenotdirectlysupportingotherstructuresandthatarenotinhighsettlementareas.UseoftheK-StiffnessMethodforgreaterwallheights,inlocationswheresettlementisanticipatedtobegreaterthan6inches,orforwallsthatsupportotherstructuresshallbeconsideredexperimental,willrequirespecialmonitoringofperformance,andtheapprovaloftheStateGeotechnicalEngineer.TheAASHTOLRFDBridgeDesignSpecificationsareapplicable,aswellasthetrafficbarrierdesignprovisionsintheWSDOTLRFDBDM,exceptasmodifiedintheprovisionsthatfollow.

15.5.3.1.1 K-StiffnessMethodLoadsandLoadFactorsInadditiontotheloadfactorsprovidedinSection3.4.1oftheAASHTOLRFDspecifications,theloadfactorsprovidedinTable 15-2shallbeusedasminimumvaluesfortheK-StiffnessMethod.Theloadfactor p to be applied to maximum load carried by the reinforcement Tmaxduetotheweightofthebackfillforreinforcementstrength,connectionstrength,andpulloutcalculationsshallbeEV,forverticalearthpressure.



TypeofLoadLoadFactor

Maximum Minimum

EV:VerticalEarthPressure:

MSEWallsoilreinforcementloads(K-StiffnessMethod,steelstripsandgrids)MSEWallsoilreinforcement/facingconnectionloads(K-StiffnessMethod,steelgridsattachedtorigidfacings)MSEWallsoilreinforcementloads(K-StiffnessMethod,geosynthetics)MSEWallsoilreinforcement/facingconnectionloads(K-StiffnessMethod,geosynthetics)

1.55

1.80

1.60

1.85

N/A

N/A

N/A

N/A

Table15-2 LoadFactorsforPermanentLoadsforinternalstabilityofMSEwalls

designedusingtheK-StiffnessMethod,p.

Loadscarriedbythesoilreinforcementinmechanicallystabilizedearthwallsaretheresultofverticalandlateralearthpressureswhichexistwithinthereinforcedsoilmass,reinforcementextensibility,facingstiffness,walltoerestraint,andthestiffnessandstrengthofthesoilbackfillwithinthereinforcedsoilmass.ThecalculationmethodforTmaxisempiricallyderived,basedonreinforcementstrainmeasurements,convertedtoloadbasedonthereinforcementstiffness,fromfullscalewallsatworkingstressconditions(seeAllen and Bathurst, 2003).ResearchbyAllen and Bathurst (2003)indicatesthattheworkingloadsmeasuredinMSEwallreinforcementremainrelativelyconstantthroughoutthewalllife,providedthewallisdesignedforastablecondition,andthattheloadstatisticsremainconstantuptothepointthatthewallbeginstofail.Therefore,theloadfactorsforMSEwallreinforcementloadsprovided in Table 15-2canbeconsideredvalidforastrengthorextremeeventlimitstate.

TheloadfactorsprovidedinTable 15-2weredeterminedassumingthattheappropriatemeansoilfrictionangleisusedfordesign.Inpractice,sincethespecificsourceofmaterialforwallbackfillistypicallynotavailableatthetimeofdesign,presumptivedesignparametersbasedonpreviousexperiencewiththematerialthatistypicallysuppliedtomeetthebackfillmaterialspecification(e.g.,GravelBorrowpertheWSDOTStandardSpecificationsforconstruction)areused(seeWSDOT GDM Chapter 5).Itislikelythatthesepresumptivedesignparametersarelowerboundconservativevaluesforthebackfillmaterialspecificationselected.TriaxialordirectshearsoilfrictionanglesshouldbeusedwiththeSimplifiedMethodprovidedintheAASHTOLRFDSpecifications,tobeconsistentwiththecurrentspecificationsandempiricalderivationfortheSimplifiedMethod,whereasplanestrainsoilfrictionanglesshouldbeusedwiththeK-StiffnessMethod,tobeconsistentwiththeempiricalderivationandcalibrationforthatmethod.Thefollowingequationsmaybeusedtomakeanapproximateestimateoftheplanestrainsoilfrictionanglebasedontriaxialordirectsheartestresults.



Fortriaxialtestdata(Lade and Lee, 1976):

ps=1.5tx17 (15-1)

Fordirectsheartestdata(basedoninterpretationofdatapresentedbyBolton (1986) and Jewell and Wroth (1987)):

ps=tan-1(1.2tands) (15-2)

Allsoilfrictionanglesareindegreesforbothequations.DirectshearortriaxialsoilfrictionanglesmaybeusedfordesignusingtheK-StiffnessMethod,ifdesired,butitshouldberecognizedthatdoingsocouldaddsomeconservatismtotheresultingloadprediction.Notethatifpresumptivedesignparametersarebasedonexperiencefromtriaxialordirectsheartestingofthebackfill,aslightincreaseinthepresumptivesoilfrictionanglebasedonequations 15-1 or 15-2isappropriatetoapply.

OtherloadsappropriatetotheloadgroupsandlimitstatestobeconsideredasspecifiedintheAASHTOLRFDspecificationsforwalldesignareapplicablewhenusingtheK-StiffnessMethodfordesign.

15.5.3.1.2 K-StiffnessMethodResistanceFactorsFortheservicelimitstate,aresistancefactorof1.0shouldbeused,exceptfortheevaluationofoverallslopestabilityasprescribedbytheAASHTOLRFDspecifications(seealsoSection 15.4.2.10).ForthestrengthandextremeeventlimitstatesforinternalstabilityusingtheK-StiffnessMethod,theresistancefactorsprovidedinTable 15-3shallbeusedasmaximumvalues.TheseresistancefactorswerederivedusingthedataprovidedinAllen and Bathurst (2003).Reliabilitytheory,usingtheMonteCarloMethodasdescribedinAllen, et al. (in press)wasappliedtostatisticallycharacterizethedataandtoestimateresistancefactors.TheloadfactorsprovidedinTable 15-2wereusedforthisanalysis.

Theresistancefactors,specifiedinTable 15-3areconsistentwiththeuseofselectgranularbackfillinthereinforcedzone,homogeneouslyplacedandcarefullycontrolledinthefieldforconformancewiththeWSDOTStandardSpecifications.TheresistancefactorsprovidedinTable 15-3 have been developed withconsiderationtotheredundancyinherentinMSEwallsduetothemultiplereinforcementlayersandtheabilityofthoselayerstoshareloadonewithanother.Thisisaccomplishedbyusingatargetreliabilityindex, ,of2.3(approximateprobabilityoffailure,Pf,of1in100forstaticconditions)anda of 1.65 (ApproximatePfof1in20)forseismicconditions.Aof3.5(approximatePfof1in5,000)istypicallyusedforstructuraldesignwhenredundancyisnotconsideredornotpresent;seeAllen et al., in press, for additionaldiscussiononthisissue.Becauseredundancyisalreadytakenintoaccountthroughthetargetvalue of selected,thefactorforredundancyprescribedintheAASHTOLRFDspecificationsshouldbesetequalto1.0.ThetargetvalueofusedhereinforseismicloadingisconsistentwiththeoverstressallowedinpreviouspracticeasdescribedintheAASHTOStandardSpecificationsforHighwayBridges(AASHTO 2002).



LimitStateandReinforcementTypeResistanceFactorInternalStabilityofMSEWalls,K-StiffnessMethod

rr ReinforcementRupture Metallic Geosynthetic0.850.80(3)

sf SoilFailure Metallic Geosynthetic0.851.00(1)

cr Connectionrupture Metallic Geosynthetic0.850.80(3)

po Pullout(2)

Steelribbedstrips(atz2m) Steelsmoothstrips Steelgrids Geosynthetic

1.101.001.000.600.50

EQrCombinedstatic/earthquakeloading(reinforcementandconnectorrupture)

Metallic Geosynthetic

1.000.95(3)

EQpCombinedstatic/earthquakeloading(pullout)(2)

Steelribbedstrips(atz2m) Steelsmoothstrips Steelgrids Geosynthetic

1.251.151.150.750.65

(1) Ifdefaultvalueforthecriticalreinforcementstrainof3.0%orlessisusedforflexiblewallfacings,and2.0%orlessforstiffwallfacings(forafacingstiffnessfactoroflessthan0.9).

(2) ResistancefactorvaluesintableforpulloutassumethatthedefaultvaluesforF*andprovidedinArticle11.10.6.3.2oftheAASHTOLRFDSpecificationsareusedandareapplicable.

(3) Thisresistancefactorappliesifinstallationdamageisnotsevere(i.e.,RFID

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