4.6 lightweight treated soil method4.6 lightweight treated soil method (1) definition and outline of...

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TECHNICAL STANDARDS AND COMMENTARIES FOR PORT AND HARBOUR FACILITIES IN JAPAN

4.6 Lightweight Treated Soil Method

(1)DefinitionandOutlineofLightweightTreatedSoilMethod

① Theprovisions in thissectioncanbeapplied to theperformanceverificationof the lightweight treatedsoilmethod.

② Thelightweighttreatedsoilmethodistoproduceartificiallightweightandstablesubsoilbyaddinglighteningmaterialsandhardeningagentstoslurry-statesoilinadjustingitsconsistingbeinghigherthanliquidlimitbymakinguseofdredgedsoilorexcavatedsoilfromconstructionsites,andthenusingtheproductasmaterialsforlandfillorbackfilling.Whenusingairfoamasthelighteningmaterial,itiscalledthefoamtreatedsoil,andwhenusingexpandedpolistyrolbeads,itiscalledthebeadstreatedsoil.Thelightweighttreatedsoilhasthefollowingcharacteristics:

(a) Theweightisapproximatelyonehalfofordinarysandintheairandapproximatelyonefifthintheseawater.Thislightnesscanpreventorreducegroundsettlementduetolandfillorbackfill.

(b)Duetoitslightweightandhighstrength,theearthpressureduringanearthquakeisreduced.Thismakesitpossibletocreatehighearthquake-resistancestructuresorreclaimedlands.

(c) Dredgedsoils,whichareregularlyproducedandtreatedaswasteinports,orwastesoilsthataregeneratedbyland–basedconstructionworks,areused.Thus,employmentofthelightweighttreatedsoilmethodcancontributetoreducingtheamountofwastematerialstobedealtwithatwastedisposalsites.

③ Refertothe“Technical Manual for the Lightweight Treated Soil Method in Ports and Airports”forfurtherdetailsontheperformanceverificationofthismethod.

(2)BasicConceptofPerformanceVerification

① Theperformanceverificationmethoddescribedin2 Foundations and3 Stability of Slopes canbeappliedtolightweighttreatedsoil.

② Apartfrommixproportiontests,theperformanceverificationmethodforlightweighttreatedsoilisbasicallythesamewiththatforotherearthstructure.73),74)

③ An example of the performance verification procedure when using the lightweight treated soil method inbackfillingforrevetmentsandquaywallsisshowninFig. 4.6.1.

PART III FACILITIES, CHAPTER 2 ITEMS COMMON TO FACILITIES SUBJECT TO TECHNICAL STANDARDS

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Determination of application of lightweight treated soil method

Assumption of strength and unit weight of lightweight treated soil

Assumption of area (or bounds, boundary) of improvementwith lightweight treated soil

Examination of ground as a whole, including lightweighttreated soil①　Evaluation of actions②　Examination of bearing capacity③　Examination of circular slip failure④　Examination of consolidation settlement⑤　Examination of liquefaction of surrounding ground

Performance verification of superstructure

Determination of strength/unit weight and area of improvement with lightweight treated soil

Fig. 4.6.1 Example of Performance Verification Procedure of Lightweight Treated Soil Method

④ Inperformanceverification,thefollowingactionsaregenerallyconsidered.

(a) Selfweightof lightweight treated soil, andselfweightofmainbody (caissons, etc.),backfillingmaterial,fillingmaterial,reclaimedsoilandmoundmaterials,(consideringbuoyancy).

(b)Earthpressureandresidualwaterpressure

(c) Surchargesincludingfixedloads,variableloadsandrepeatedloads

(d)Tractiveforceofshipandreactionoffenders

(e) ActionsinrespectofgroundmotionIncalculationsofearthpressureandearthpressureduringearthquakes,theconceptsin4.18 Active Earth Pressure of Geotechnical MaterialTreated with Stabilizer canbeapplied.

⑤ Thepropertiesoflightweighttreatedsoilshallbeevaluatedbymeansoflaboratoryteststhattakeaccountoftheenvironmentalandconstructionconditionsofthesite.Theymaybeevaluatedasfollows:

(a) UnitweightTheunitweightmaybesetwithinarangeofγt=8-13kN/m3byadjustingtheamountoflighteningmaterialandaddedwater.Whenusedinportfacilities,thereisariskofflotationincaseofariseofseawaterleveliftheunitweightislessthanthatofseawater.Normally,therefore,thecharacteristicvalueoftheunitweightisfrequentlysettothefollowingvalues:belowwaterlevel:

foruseuderwater: γtk=11.5-12kN/m3

foruseinair: γtk=10kN/m3

Theunitweightoflightweighttreatedsoilwillvarydependingontheenvironmentalconditionsduringand after placement, and particularly the intensity ofwater pressure. Therefore, these factors should beconsideredinadvanceinthemixturedesign.75),76)

(b)Strength77)The static strength of lightweight treated soil ismainly attributable to the solidified strength due to thecement-basedsolidifyingagent.Standarddesignstrengthisevaluatedbyunconfinedcompressivestrengthquandcangenerallybesetintherangeof100–500kN/m2.Becauseairfoamorexpandedbeadsareincludedinthetreatedsoil,noincreaseinstrengthcanbeexpectedduetoincreasedconfiningpressure.However,theresidualstrengthisapproximately70%ofthepeakstrength.Thecharacteristicvalueofcompressivestrength

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shallbethestandarddesignstrengthandbesettoanappropriatevaluecapableofsatisfyingperformancerequirementssuchasstabilityofthesuperstructureorthegroundasawhole. Asthecharacteristicvalueofshearstrength,undrainedshearstrengthcucanbeused.Thevalueofcucanbecalculatedusingthefollowingequation.

(4.6.1)

(c) TheconsolidationyieldstressPy maybecalculatedusingthefollowingequation:

(4.6.2)

(d)DeformationmodulusE50When testsareconductedconsideringfinepoints suchasmeasurementof smallamountsofdeformation,finishingoftheendsofspecimens,thetestvalueassuchisusedasthedeformationmodulusE50.Whensuchtestsarenotpossible,themoduluscanbeestimatedfromtheunconfinedcompressivestrengthquusingthefollowingequation:

(4.6.3) Thedeformationmodulusshownabovecorrespondstoastrainlevelof0.3–1.0%.

(e) Poisson’sratioPoisson’sratiooflightweighttreatedsoilvariesdependingonthestresslevelandthestatebeforeoraftertheattainmentofpeakstrength.Whenthesurchargeislessthantheconsolidationyieldstressoftreatedsoil,thefollowingmeanvaluesmaybeused:

airfoamedtreatedsoil: v =0.10expandedbeadstreatedsoil: v =0.15

(f) DynamicpropertiesTheshearmodulusG,dampingfactorh,straindependencyofG andh,andPoisson’sratiov usedindynamicanalysis should be obtained from laboratory tests. Theymay be estimated from the estimationmethodconductedfortheordinarysoilsasasimplifiedmethodinreferencetotheresultsofultrasonicpropagationtest.

(3)ExaminationofAreaofImprovement78)

① Theareatobefilledwiththelightweighttreatedsoilneedstobedeterminedasappropriateinviewofthetypeofstructuretobebuiltandtheconditionsofactionsaswellasthestabilityofthestructureandthegroundasawhole.

② Theextentoffillingareawithlightweighttreatedsoilisusuallydeterminedtomeettheobjectiveoflightening.Whenthemethodisappliedtocontrolsettlementorlateraldisplacement,itisdeterminedfromtheallowableconditions for settlement or displacement; to secure stability, it is determined from the condition of slopestability;toreduceearthpressure,itisdeterminedfromtherequiredconditionsforearthpressurereduction.79)

(4)ConceptofMixProportion

① Designofmixproportionshallbeconductedtoobtainthestrengthandtheunitweightrequiredinthefield.

② Typesofsolidifyingagentsandlighteningagentsshallbedeterminedaftertheirefficiencyhasbeenconfirmedintests.

③ Thetargetstrengthinlaboratorymixproportiontestsshallbesettoavalueobtainedbymultiplyingthestandarddesignstrengthbyarequiredadditionalrateα,consideringdifferencesinlaboratorymixproportionstrengthandin-situstrengthandvariance.Therequiredadditionalrateαisexpressedbytheratioofthestrengthinlaboratorymixproportiontestsandstandarddesignstrength.Normally,thefollowingvaluecanbeused.

a =2.2


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4.7 Blast Furnace Granulated Slag Replacement Method

(1)BasicConceptofPerformanceVerification

①Whenusingblastfurnacegranulatedslagasbackfillforquaywallsorrevetments,landfill,surfacecoveringforsoftsubsoilandsandcompactionmaterial,thecharacteristicsofthematerialsshallbeconsidered.

② Blastfurnacegranulatedslagisagranularmaterial.However,ithasalatenthydraulichardeningpropertynotfoundinnaturalsandandisamaterialwhichsolidifieswithlapseoftime.83)Whenusedinbackfill,ifitsgranularstateandsolidifiedstatearecompared,thegranularstategenerallygivesadangerousstateintheperformanceverificationinmanycases.Provided,however,thatitispreferabletoconductanadequateexamination,judgingtheindividualconditions,incaseswherethesolidifiedstatemayposearisktothefacilities.

(2)PhysicalProperties

①Whenusinggranulatedblastfurnaceslag,itsphysicalpropertiesarepreferablytobeascertainedinadvance.

② Blastfurnacegranulatedslagisinastatelikecoarsesandwhenshippedfromplants.Theimportantcharacteristicsofphysicalpropertiesoftheblastfurnacegranulatedslagsareitssmallunitweightlatenthydraulichardeningproperty.

③ GrainsizedistributionTherangeshowninFig. 4.7.1isgenerallystandardforthegrainsizedistributionofblastfurnacegranulatedslag. The standard grain size of blast furnace granulated slag is 4.75mm or less, and its fines content isextremelysmall.Thus,ithasastable,comparativelyuniformgrainsizedistribution.Thecoarsesandregionaccounts for the largerpart of thegrain sizes,with auniformity coefficient of2.5–4.2 and a coefficient ofcurvatureof0.9-1.4.

10

6

8

4

2

0 0. 1. 10. 50.

Perc

enta

ge fi

ner b

y w

eigh

t (%

)

Grain size D (mm)

Fig. 4.7.1 Standard Grain Size Distribution of Blast Furnace Granulated Slag

④ Unitweight83)Blastfurnacegranulatedslagislighterinweightthannaturalsandbecauseitsgrainscontainairbubblesandithasalargevoidratioduetoitsangularshapeandsinglegrainsizedistribution.Accordingtotheresultsofstudiestodate,thewetunitweightofgranulatedslagrangesfrom9-14kN/m3,anditsunitweightinwaterisapproximately8kN/m3.

⑤ PermeabilityThecoefficientofpermeabilityinthegranularstatediffersdependingonthevoidratiobutisroughly1×100-1×10-1cm/s.Thecoefficientofpermeabilitydecreaseswithsolidification,buteveninthiscaseisapproximately1×10-2cm/s.85)Provided,however,thatwhenconstructionisconductedusingmethodsthatcausecrushingoftheparticles,forexample,inthesandcompactionpilemethod,thecoefficientofpermeabilitybecomesextremelysmall.Cautionisrequiredinsuchcases.

⑥ CompressibilityThe time-dependentchangeofcompressibilityofblast furnacegranulatedslagusedforbackfill, landfill,orsurfacecoveringcanbeignored.

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⑦ AngleofshearresistanceandcohesionInthegranularstate,cohesioncanbetreatedasnon-existent.Theangleofshearresistanceinthiscaseis35ºorgreater.Whensolidified,shearstrengthisgreaterthaninthegranularstate.83)Inthiscase,theeffectsofboththeangleofshearresistanceandcohesiononmaximumshearstrengthcanbeconsidered.However,inexaminingresidualstrength,onlytheeffectoftheangleofshearresistanceshouldbeconsidered.

⑧LiquefactionduringanearthquakeWhenblastfurnacegranulatedslagisusedinbackfill,itsolidifiesinseveralyearsbecauseofitslatenthydraulichardeningproperty.Whensolidificationcanbeexpected,liquefactioncanbeignored.However,thereisariskofliquefactionforblastfurnacegranulatedslagthathasnotyetsolidified.Thereforeinthiscase,thepossibilityofliquefactionshouldbeexamined,treatingtheblastfurnacegranulatedslagasagranularmaterial.

(3)ChemicalProperties

①Whenusingblastfurnacegranulatedslag,appropriateconsiderationshallbegiventoitschemicalproperties.

② ThepHvalueof the leachedwaterfromblastfurnacegranulatedslagissmaller thanthepHof the leachedwaterfromcementandlimestabilizationtreatment.Furthermore,itspHisalsoreducedbytheneutralizingandbufferingactionoftheseawatercompositionanddilutionbyseawater.Forthisreason,inordinarycases,itisnotnecessarytoconsidertheeffectofthepHontheenvironment.


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4.8 Premixing Method4.8.1 Fundamentals of Performance Verification

(1)ScopeofApplication

① Theperformanceverificationdescribedinthissectionmaybeappliedtotheperformanceverificationofthesubsoiltreatedbythepremixingmethodaimedatearthpressurereductionandliquefaction,prevention.

② Themeaningsofthetermsusedinconnectionwiththismethodareasfollows: Treatedsoil: Soilimprovedbystabilizer. Treatedsubsoil: Subsoilimprovedbyfillingwithtreatedsoil. Areaofimprovement: Areatobefilledwithtreatedsoil. Stabilizercontent: Weightratioofstabilizertodryweightofparentmaterial,expressedasa percentage. Reductionofearthpressure:Measurestoreduceearthpressureagainstwalls(activeearthpressure).

③ In thepremixingmethod, stabilizerandantisegregationagentareadded into soil for reclamation,mixed inadvanceandusedaslandfillmaterialstodevelopstableground.Thesubsoilimprovementismaterializedascement-basedstabilizersaddcohesion to thesoilused in landfillbymeansofchemicalsolidificationactionbetweensoilandstabilizer.Thismethodcanbeappliedtobackfillbehindquaywallsandrevetments,fillingofcellular-bulkhead,replacementafterseabottomexcavationandrefilling.

④ Soilsapplicabletothetreatmentmentionedhereinaresandandsandysoils,excludingcohesivesoil.Thisisbecausethemechanicalpropertiesofthetreatedcohesivesoildifferconsiderablydependingonthecharacteristicofsoil.Itisnecessarytoconductappropriateexaminationaccordingtothepropertyofsoilsubjecttotreatment.

⑤ Besidesreducingearthpressureandpreventingliquefaction,thismethodcanalsobeusedtoimprovethesoilstrengthnecessaryforconstructionoffacilitiesonreclaimedlands.Inthiscase,thestrengthoftreatedgroundshouldbeevaluatedappropriately.

⑥ For items inconnectionwith theperformanceverificationandexecutionwhenusing thepremixingmethodwhicharenotmentionedherein,Reference1)canbeusedasareference.

(2)BasicConcepts

① Inperformanceverification,itisnecessarytodeterminetherequiredstrengthofthetreatedsoilcorrectly,andtodeterminethestabilizercontentandareaofimprovementappropriately.

②Whenevaluatingtheearthpressurereductioneffectorexaminingthestabilityofthesubsoilagainstcircularslipfailure,thetreatedsoilshouldberegardedasa“c-φmaterial”.

③ Thetreatedsubsoilmaybethoughttoslideasarigidbodyduringanearthquakebecausethetreatedsubsoilhasarigidityconsiderablygreaterthanthatofthesurroundinguntreatedsubsoil.Therefore,whendeterminingthe area of improvement, the stability against sliding of the subsoil including superstructures shall also beexamined.

④ It ispreferable todetermine thestandarddesignstrengthandareaof improvementof treatedsubsoilby theprocedureshowninFig. 4.8.1.

⑤ Ingeneral,whentheparentsoilissandysoil,thetreatedsoilisregardedasc-ømaterial.Therefore,theshearstrengthofthetreatedsoilcanbecalculatedusingequation(4.8.1).

(4.8.1)where

τf :shearstrengthoftreatedsoil(kN/m2) σ’ :effectiveconfiningpressure(kN/m2) c :cohesion(kN/m2) φ :angleofshearresistance(º)

candφcorrespondtothecohesioncdandangleofshearresistanceød obtainedbytheconsolidated-drainedtriaxialcompressiontest,respectively.

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Determination of standard design strengthand area of improvement of treated subsoil

Evaluation of actions

Preliminary survey and tests of untreated and treated soil

Determination of angle of shear resistance (φ) of treated subsoil

Examination of liquefaction countermeasuresand earth pressure reduction effect

Stability of facilities

Assumption of cohesion (c) and area of improvement of treated subsoil

Fig. 4.8.1 Example of Performance Verification Procedure for Premixing Method

4.8.2 Preliminary Survey

(1)Thecharacteristicsofsoilusedinthepremixingmethodneedtobeevaluatedappropriatelybypreliminarysurveysandtests.

(2)Preliminarysurveysandtestsincludesoiltestsonparticledensity,watercontent,grainsizedistribution,maximumandminimumdensitiesofsoilstobeusedforfilling,andsurveysonrecordsofsoilpropertiesandfieldtestsoftheexistingreclaimedgroundnearby.

(3)Becausethewatercontent,andfinescontentofsoilsusedinreclamationwillaffecttheselectionofthemixingmethodwhenmixingthestabilizerandstrengthgrainaftermixing,cautionisnecessary.

(4)Thedensityofthetreatedsubsoilafterplacementshouldbeestimatedproperlyinadvance.Becausethedensityofthesubsoilafterreclamationisbasicdatafordeterminingthedensityforsamplesinlaboratorymixproportiontestsandhasamajoreffectonthetestresults,cautionisnecessary.

4.8.3 Determination of Strength of Treated Soil

(1)Thestrengthoftreatedsoilneedstobedeterminedinsuchawaytoyieldtherequiredimprovementeffects,bytakingaccountofthepurposeandconditionsofapplicationofthismethod.

(2)Forthepurposeofreducingtheearthpressure,thecohesionc oftreatedsoilneedstobedeterminedsuchthattheearthpressureisreducedtotherequiredvalue.

(3)Forthepurposeofpreventingliquefaction,thestrengthoftreatedsoilneedstobedeterminedsuchthatthetreatedsoilwillnotliquefy.

(4)Thereisasignificantrelationshipbetweentheliquefactionstrengthandtheunconfinedcompressivestrengthoftreatedsoils.Itisreportedthattreatedsoilswiththeunconfinedcompressivestrengthof100kN/m2ormorewillnotliquefy.Therefore,whenaimingtopreventliquefaction,theunconfinedcompressivestrengthasanindexforstrengthoftreatedsoilshouldbesetat100kN/m2.Whentheunconfinedcompressivestrengthoftreatedsoilissetatlessthan100kN/m2,itispreferablethatcyclictriaxialtestsshouldbeconductedtoconfirmthatthesoilwillnotliquefy.

(5)Indeterminingthecohesionoftreatedsoil,theinternalfrictionangleφ oftreatedsoilisfirstestimated.Then,thecohesionisdeterminedbyreversecalculationusinganearthpressurecalculationformulathattakesaccountofcohesionandangleofshearresistancewiththetargetreducedearthpressureandtheestimatedangleofshearresistanceφ .


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(6)Accordingtotheresultsofconsolidated-drainedtriaxialcompressiontestsoftreatedsoilwithastabilizercontentoflessthan10%,theangleofshearresistanceofthetreatedsoilisequaltoorslightlylargerthanthatoftheparentsoil. Accordingly, in theperformanceverification, tobeon thesafeside, theangleof shear resistanceof thetreatedsoilcanbeassumedtobethesameasthatoftheuntreatedsoil.

(7)Whenobtainingtheangleofshearresistancefromatriaxialcompressiontest, theangleofshearresistanceisobtainedfromtheconsolidated-drained triaxialcompression testbasedon theestimateddensityandeffectiveoverburden pressure of the subsoil after landfilling. The angle of shear resistance used in the performanceverification isgenerallysetatavalue5-10ºsmaller than thatobtainedfromtests. Whena triaxial test isnotperformed,øcanbeobtainedfromtheestimatedN-valueofthesubsoilafterlandfilling.Inthatcase,theN-valueoftheuntreatedsubsoilshallbeused.

4.8.4 Design of Mix Proportion

(1)Mixproportionoftreatedsoilshallbedeterminedbyconductingappropriatelaboratorymixingtests.Areductionofstrengthshallbetakenintoaccountbecausethein-situstrengthmaybelowerthanthestrengthobtainedfromlaboratorymixingtests.

(2)Thepurposeoflaboratorymixingtestsistoobtaintherelationshipbetweenthestrengthoftreatedsoilandthestabilizercontent,and todetermine thestabilizercontentsoas toobtain the requiredstrengthof treatedsoil.Therelationshipbetweenthestrengthoftreatedsoilandthestabilizercontentisgreatlyaffectedbythesoiltypeandthedensityofsoil.Therefore,testconditionsoflaboratorymixingtestsispreferabletobeassimilartofieldconditionsaspossible.

(3)Forthepurposeofreducingearthpressure,consolidated-drainedtriaxialcompressiontestsshouldbecarriedouttoobtaintherelationshipamongthecohesionc,theangleofshearresistanceφ ,andthestabilizercontent.Forthepurposeofpreventingliquefaction,unconfinedcompressiontestsshouldbeconductedtoobtaintherelationshipbetweentheunconfinedcompressivestrengthandthestabilizercontent.

(4)Itisimportanttograspthedifferencebetweenin-situandlaboratorystrengthswhensettingtheincreasefactorformixproportiondesigninthefield.Accordingtopastexperience,thelaboratorystrengthislargerthanthein-situstrength,andtheincreasefactorofα=1.1to2.2isused.Here,theincreasefactorαisdefinedastheratioofthelaboratorytothefieldstrengthsintermsofunconfinedcompressivestrength.

4.8.5 Examination of Area of Improvement

(1)Theareatobeimprovedbythepremixingmethodneedstobedeterminedasappropriateinviewofthetypeofstructure tobeconstructedandtheconditionsofactionsaswellas thestabilityofsubsoilandstructuresasawhole.

(2)Forthepurposeofreducingearthpressure,theareaofimprovementneedstobedeterminedinsuchawaythattheearthpressureoftreatedsubsoilactingonastructureshouldbesmallenoughtoguaranteethestabilityofthestructure.

(3)Forthepurposeofpreventingliquefaction,theareaofimprovementneedstobedeterminedinsuchawaythatliquefactionintheadjacentuntreatedsubsoilwillnotaffectthestabilityofstructure.

(4)TheactionsandresistancestobeconsideredonthefacilitiesandthetreatedsubsoilinthecasethatliquefactionisexpectedontheuntreatedsubsoilbehindthetreatedsubsoilandinthecasenoliquefactionisexpectedareshowninFig. 4.8.2andFig. 4.8.3,respectively.

(5)Foreitherreductionofearthpressureorpreventionofliquefaction,itisnecessarytoconductanexaminationofstabilityagainstslidingduringactionofgroundmotion,includingthetreatedsubsoilandtheobjectfacilities,andcircularslipfailureinthePermanentsituation.

① ExaminationofslidingduringactionofgroundmotionExaminationofslidingduringactionofgroundmotionisperformedbecausethereisapossibilitythatthetreatedsubsoilmayslideasarigidbody.Asthepartialfactorγawhichisusedinthiscase,ingeneral,anappropriatevalueof1.0orhigherisassumed,andasthecharacteristicvalueofthecoefficientoffrictionofthebottomofthetreatedsubsoil,0.6canbeused.Provided,however,thatwhentheoriginalsubsoilinthecalculationoftheslidingresistanceofthebottomofthetreatedsubsoilisclay,thecohesionoftheoriginalsubsoilcanbeused.Theresultantofearthpressureinequation(4.8.2) ofstabilityagainstslidingwhenuntreatedgrounddoesnotliquefy,aspresentedbelow,showsasimplecaseinwhichtheresidualwaterlevelisatthegroundsurface.Whentheresidualwaterlevelexistsundergroundandtheuntreatedgroundliquefies,itisconsideredthatthesubsoilabovetheresidualwaterlevelalsoliquefiesbypropagationofexcesswaterpressurefromthelowersubsoil.

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Suchcasescanbetreatedasliquefactionreachingthesurface. Whenthepurposeisreductionofearthpressure,ingeneral,theareaofimprovementtakestheshapeofthetreatedsubsoilasshowninFig. 4.8.2,suchthattheactivecollapseplaneiscompletelyincludedinthestabilizedbody.Ontheotherhand,whenthepurposeisacountermeasureagainstliquefaction,iftheshapeofthetreatedsubsoilshowninFig. 4.8.2isadopted,liquidpressurefromtheliquefiedsubsoilwillactupwardonthetreatedsubsoil,reducingtheweightofthetreatedsubsoil.BecausetheshapeofthetreatedsubsoilshowninFig. 4.8.2isdisadvantageousforslidingincomparisonwiththeshapeofthetreatedsubsoilshowninFig. 4.8.3,whenthepurposeisuseasaliquefactioncountermeasure,theshapeofthetreatedsubsoilshowninFig. 4.8.3isgenerallyused.

(a)WhenpurposeisreductionofearthpressureIf the positive direction of the respective actions and resistances is defined as shown inFig. 4.8.2, theverificationofstabilityagainstslidingcanbeperformedusingequation (4.8.2).Inthefollowing,thesymbolγisthepartialfactorofitssubscript,andthesubscriptskandddenotethecharacteristicvalueanddesignvalue,respectively.

(4.8.2) Inthisequation,thedesignvaluescanbecalculatedasfollows.

(whenoriginalsubsoilundertreatedsubsoilissand)

(whenoriginalsubsoilundertreatedsubsoilisclay)

(4.8.3)

where R1 :frictionalresistanceofbottomsurfaceofstructure(ab)(kN/m) R2 :frictionalresistanceofbottomsurfaceoftreatedsubsoil(bc)(kN/m) Pw1 :resultantofhydrostaticwaterpressureactingonfrontofstructure(af)(kN/m) Pw2 :resultantofdynamicwaterpressureactingonfrontofstructure(af)(kN/m) Pw3 :resultantofhydrostaticwaterpressureactingonbackoftreatedsubsoil(cd)(kN/m) H1 :inertiaforceactingonstructure(abef)(kN/m) H2 :inertiaforceactingontreatedsubsoilbody(bcde)(kN/m) Ph :horizontalcomponentofresultantofactiveearthpressureduringearthquakefromuntreated

subsoilactingonbackoftreatedsubsoil(cd)(kN/m) Pv :vertical component of resultant of active earth pressure during earthquake from untreated

subsoilactingonbackoftreatedsubsoil(cd)(kN/m) ρwg :unitweightofseawater(kN/m3) w' :unitweightofuntreatedsubsoilinwater(kN/m3) kh :seismiccoefficientforverification Ka :coefficientofactiveearthpressureduringearthquakeofuntreatedsubsoil h1 :waterlevelatfrontofstructure(m) h2 :residualwaterlevel,forsimplicityinthisexplanation,theresidualwaterlevelinFig. 4.8.2is

assumedtobethegroundsurface. δ :frictionangleofwallbetweentreatedsubsoilanduntreatedsubsoil(cd)(º)


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φ :angleofbackoftreatedsubsoil(cd)toverticaldirection(º),counterclockwiseispositive;inFig. 4.8.2,thevalueofφisnegative.

f1 :coefficientoffrictionofbottomofstructure f2 :coefficientoffrictionofbottomoftreatedsubsoil(=0.6) c :cohesionoforiginalsubsoil(kN/m2) bc :lengthofbottomoftreatedsubsoil(bc)(m) γa :structuralanalysisfactor

(b)WhenusedasliquefactioncountermeasureIfthepositivedirectionoftherespectiveactionsandresistancesisdefinedasshowninFig. 4.8.3,verificationofstabilityagainstslidingcanbeperformedusingequation (4.8.4).Inthefollowing,thesymbolγisthepartialfactorofitssubscript,andthesubscriptskandddenotethecharacteristicvalueanddesignvalue,respectively.Whentheuntreatedsubsoilatthebackofthetreatedsubsoilliquefy,thestaticpressureanddynamicpressurefromtheuntreatedsubsoilgenerallyactonthebackofthetreatedsubsoilasshowninFig. 4.8.3.Staticpressurecanbecalculatedbyadditionhydrostaticpressuretoearthpressure,assumingthecoefficientofearthpressuretobe1.0.Dynamicpressurecanbecalculatedusingequation(2.2.1)andequation (2.2.2)shownin Part II, Chapter 5, 2.2 Dynamic Water Pressure.Provided,however,thattheunitweightofwaterinequation (2.2.1)andequation (2.2.2) isreplacedwiththeunitweightofsaturatedsoil.

(4.8.4)

Inthisequation,thedesignvaluescanbecalculatedasfollows.

(whenoriginalsubsoilunder

treatedsubsoilissand)(whenoriginalsubsoilunder

treatedsubsoilisclay)

(4.8.5)

where R1 :frictionalresistanceofbottomsurfaceofstructure(ab)(kN/m) R2 :frictionalresistanceofbottomsurfaceoftreatedsubsoil(bc)(kN/m) Pw1 :resultantofhydrostaticwaterpressureactingonfrontofstructure(af)(kN/m) Pw2 :resultantofdynamicwaterpressureactingonfrontofstructure(af)(kN/m) H1 :inertiaforceactingonstructure(abef)(kN/m) H2 :inertiaforceactingontreatedsubsoilbody(bcde)(kN/m) Ph :horizontalcomponentofresultantofactiveearthpressureduringearthquakefromuntreated

subsoilactingonbackoftreatedsubsoil(cd)(kN/m) ρwg :unitweightofseawater(kN/m3) w’ :unitweightofuntreatedsubsoilinwater(kN/m3) kh :seismiccoefficientforverification Ka :coefficientofactiveearthpressureduringearthquakeofuntreatedsubsoil h1 :waterlevelatfrontofstructure(m) h2 :water levelused incalculatingPh due to liquefaction(Thiswater level isassumedtobe the

groundsurfacelevel.) φ :angleofbackoftreatedsubsoil(cd)toverticaldirection(º),counterclockwiseispositive;inFig.

4.8.3,thevalueofφisnegative.

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f1 :coefficientoffrictionofbottomofstructure f2 :coefficientoffrictionofbottomoftreatedsubsoil(=0.6) c :cohesionoforiginalsubsoil(kN/m2) bc :lengthofbottomoftreatedsubsoil(bc)(m) γa :structuralanalysisfactor

(c) PartialfactorsForallpartial factors in theexaminationof slidingduringactionofgroundmotion, including the treatedsubsoilandtheobjectfacilities,1.00canbeused.

② ExaminationofstabilityagainstcircularslipfailureinPermanentsituationFortheexaminationofstabilityagainstthecircularslipfailureinthePermanentsituation,3 Stability of Slopescanbeusedasareference.

(6)Whenitisnotpossibletosecurethestabilityofthefacilitiesorthegroundasawhole,itisnecessarytomodifytheareaofimprovement,ortoincreasethestandarddesignstrengthofthetreatedsoil,etc.

h 1

wP 1

wP 2

f e

a b

d

c

H12H

R1 R 2

W '1 W '2W1 W2

(+)(–)

Pv

Ph

Pw3

h2

Structure Treated subsoil Untreated subsoil (not liquefied)

ψ

Fig. 4.8.2 Diagram of Actions when Purpose is Reduction of Earth Pressure

(+)(–)

Structure Treated subsoil Untreated subsoil (not liquefied)

ψ

f e

a b c

d

h 1

wP 1

wP 2

H1

W1 W '1

R1 R 2

2H

W2 W '2

Pv

Ph

h2

Static pressure(earth + water)Static pressure(earth + water)

Dynamic pressure(earth + water)

Dynamic pressure(earth + water)

Fig. 4.8.3 Diagram of Actions when Used as Liquefaction Countermeasure


–529–

4.9 Sand Compaction Pile Method (for Sandy Soil Ground)4.9.1 Basic Policy for Performance Verification

(1)Theperformanceverificationofthesandcompactionpilemethodtodensifysandysoilsneedstobeconductedappropriatelyafterexaminingthecharacteristicsofsubsoilpropertiesandconstructionmethods,aswellasbytakingaccountofthepastconstructionrecordsandtheresultsoftestexecution.

(2)PurposeofImprovementThepurposeofimprovingloosesandysubsoilcanbeclassifiedinto(a) improvingliquefactionstrength,(b)reducingsettlement,and(c) improvingthestabilityofslopesorbearingcapacity.

(3)FactorsaffectingcompactioneffectInmanycases,compactiontofirmgroundofloosesandsubsoilcannotbeachievedadequatelybyvibrationorimpactfromthesurface.Therefore,themethodsnormallyadoptedaretoconstructpilesofsandorgravelintheloosesandysubsoilusinghollowsteelpipesortodrivespecialvibratingrods,soastovibratethesurroundingground.

4.9.2 Verification of Sand Supply Rate

(1) Intheverificationofthesandsupplyrate,improvementratioorreplacementratio,itisnecessarytoconductanadequateexaminationofthecharacteristicsoftheobjectground,necessaryrelativedensity,andN-value.

(2)SettingofTargetN-valueItisnecessarytosettheN-valueoftheimprovementtarget.Furthermore,whenthepurposeofthesandcompactionpilemethodisaliquefactioncountermeasure,itisnecessarytosettheN-valuetoavalueatwhichitisjudgedthatliquefactionwillnotoccurundertheobjectgroundmotion.TheN-valueisdefinedasthelimitN-value.

(3)SandSupplyRateThesandsupplyrateisthepercentageofthesandpilesafterimprovementintheoriginalsubsoil,asshowninequation (4.9.1).

(4.9.1)

(4)DeterminationofSandSupplyRatewhenExistingDataarenotavailable87)Thesandsupply rate isdeterminedusing the relationshipbetween thesandsupply rateand theN-valueafterimprovementshownbythefollowingequation.Provided,however,thattheexistingdatausedinderivingthefollowingequation (4.9.2)throughequation(4.9.9)aresandsupplyrateFV=0.07-0.20andfinescontentFc=60%orless.Accordingly,cautionisnecessarywhenusingconditionsoutsideofthisrange.

(4.9.2)where

N1 :N-valueaftersandsupply CM :coefficient;here,CM=(1/0.16)2maybeused. κ :coefficient;hereκ=5·10–0.01Fcmaybeused.

c :coefficient;here maybeused.

Fc :coefficient;finescontent(%) γi* :coefficientcalculatedusingequation (4.9.3)

(4.9.3)

where N0 :N-valueoforiginalsubsoil A :coefficientcalculatedusingequation (4.9.4)

–530–


(4.9.4)where

σv’ :effectiveoverburdenpressurewhenmeasuringN-value(kN/m2)

Equation (4.9.2)canbesolvedforthesandsupplyrateFv,andthesandsupplyrateforobtainingthetargetN-valuecanbeobtainedusingthefollowingequation.

(4.9.5)

Becauseequation (4.9.2)andequation (4.9.3)donotconsidertheeffectoftheincreaseinlateralpressureduetosandsupplyortheeffectofcoefficientofearthpressureatrestK0,thereisatendencytounderestimatetheN-valueaftersandsupplywhenthesandsupplyrateislarge.WhenaresultisobtainedinwhichthesandsupplyrateexceedsFV=0.2,amethod88)usingthefollowingequation,whichconsiderstheeffectofK0,isalsoavailable.Provided,however,thatcautionisnecessary,aspredictiveaccuracydeterioratesduetothelargevariationintherelationshipbetweenthesandsupplyrateandthevalueofK0usedinthederivationprocessofthefollowingequation.Accordingly,inordertoavoiddangerousresults,whenusingthefollowingequation,itshallbeassumedthatFV=0.2,evenwhentheresultsofcalculationofthesandsupplyrateforobtainingthetargetN-valuearelessthanFV=0.2.

(4.9.6)where

CM :coefficient;here,CM=(1/0.16)2maybeused. κ :coefficient;hereκ=4・10–0.01Fcmaybeused.

c :coefficient;here

maybeused.

γi* :coefficientcalculatedusingequation (4.9.7)

(4.9.7)

where AK1 :coefficientcalculatedusingequation (4.9.8)

(4.9.8)

Here,α is a coefficient expressing the rateof increase inK0 relative to the sand supply rate, andcanbeassumedtobeα=4.

AK0 :coefficientcalculatedusingequation (4.9.9)

(4.9.9)

συ’ :effectiveoverburdenpressurewhenmeasuringN-value(kN/m2)

Provided,however,thatwhenthesandsupplyrateforthetargetN-valueisFV<0.2,FV=0.2shallbeused.

(5)SettingofSandSupplyRate,whentheExistingDataareAvailableThe increase in theN-value after execution of the sand compaction pile method is strongly affected by thesubsoil characteristics and the executionmethod. Therefore,when abundant execution data are available fortheconstructionsiteorwhentestexecutionisperformed,determinationbasedonactualrecordsofexecutionis


–531–

preferable,themethodin(4)notwithstanding.Whenthemethodin(4)istobeused,theresettingoftheparameterκinequation (4.9.5) shouldbedoneasfollowsusingtheexistingdata.Whenusinganewcompactingmethod,itisadvisabletoresettheparameterκinequation (4.9.5) bythefollowingmethodusingowndata. Theparameterκofequation(4.9.5)canbegivenbyequation (4.9.10).Therefore,ifdataareavailablefortheN-valueaftersandsupplyinthesandcompactionpilemethod,theN-valuebeforesandsupply,thefinescontent,andthesandsupplyrate,κcanbecalculatedbyusingequation(4.9.10).

(4.9.10)

where γi* :coefficientcalculatedusingequation (4.9.11)

(4.9.11)

CM :coefficient;hereCM=(1/0.16)2maybeused.

c :coefficient;here maybeused.

A :coefficient;here (4.9.12)

It is permissible to determine the relational equation for κ and thefines content byobtainingκ from therespectivesandsupplyratesandN-valuesbeforeandafterimprovement,andarrangingtherelationshipbetweenκandthefinescontentasshowninFig. 4.9.1.Here,itisbasicallyassumedthattherelationalequationbetweenκandthefinescontentisanexponentialfunctionasshownin(4). Inparametersetting,whenthereisalargedifferenceinthefinescontentbeforeandafterimprovement,andwhentheN-valuebeforeimprovementislarger,thedataforthatpointshallnotbeused.WhentherelationshipbetweenthevalueofK0andthesandsupplyrateisactuallymeasured, theparametersinequation (4.9.6)andequation (4.9.7)whichconsidertheinfluenceofthevalueofK0canbereset.Foritemsrelatedtoparametersettinginthiscaseandrelatedmatters,Reference2)canbeusedasreference.

Fines content (%)0 10 20 30 40 50 60

0

5

15

20

25

10

Sand supply rate Fv = 0.7 ~ 0.20

κ

Exponential regression curve of plotApproximation line at κ = 5・10-0.01Fc

Fig. 4.9.1 Relationship between κ and Fines Content

–532–


(6)OtherMethodsofSettingSandSupplyRateThemethodsofsettingthesandsupplyrateshownintheabove(4)and(5)considercompactionoftheoriginalsubsoilresultingfromrepeatedshearbysandsupplyundersandpiledriving,andwerederivedbyanalysisofpastexecutiondata.Inadditiontothesemethods,methodsreferredtoasAmethod,Bmethod,andCmethodhavealsobeenproposedandhavebeenusedforsometime.89)IntheAmethod,therelationshipbetweentheN-valuebeforeandaftersandsupplyisshowninchartform,usingthesandsupplyrateasaparameter,andthusenablessimplecalculationofthesandsupplyrate.Provided,however,thatthismethodhaslowgeneralityincomparisonwithothermethodsbecauseitdoesnotconsidertheeffectoftheoverburdenpressureortheeffectofthefinescontent.TheBmethodusesempiricalformulaefortherelativedensity,N-value,effectiveoverburdenpressure,andgrainsize,andobtainsthesandsupplyrateforthetargetN-valueassumingthatthegroundiscompactedonlybytheamountofthesandpilessupplied.Provided,however,thatthismethoddoesnotconsidertheeffectofthefinescontent.TheCmethodisproposedusingaconceptwhichisbasicallythesameasintheBmethod.ThemajordifferencewiththeBmethodisthefactthattheeffectofthefinescontentisconsidered.Thus,theCmethodhasthehighestgeneralityofthesethreemethods.TheDmethodisalsoproposed.89)TheDmethodconsiderstheeffectofgroundriseaccompanyingdrivingofthesandpiles,whichisnotconsideredintheCmethod. Here,theCmethodisdescribedhere,asthismethodhasthehighestgeneralityandmostextensiverecordofactualresultsamongthethreemethodsinconventionaluse.90)

① emaxandeminareobtainedfromthefinescontentFc.

(4.9.13) (4.9.14)

② The relative densityDr0 and e0 are obtained from theN-value of the original subsoilN0 and the effectivesurchargepressureσv'’.

(4.9.15)

(4.9.16)

③ ThereductionrateβfortheincreaseintheN-valueduetothefinesfractionisobtained.

(4.9.17)

④ AcorrectedN-value(N1’)isobtainedfromtheN-value(N1)calculatedassumingnofinesfraction,consideringthereductionrateβ.

(4.9.18)

⑤ e1isobtainedusingequation (4.9.16)intheabove②bysubstitutingN1’forN0.

⑥ SandsupplyrateFvisobtainedusingequation(4.9.19)frome0,e1.

(4.9.19)


–533–

4.10 Sand Compaction Pile Method for Cohesive Soil Ground4.10.1 Basic Policy of Performance Verification

[1] Scope of Application

Thescopeofapplicationoftheperformanceverificationofthesandcompactionpilemethod,SCPmethod,describedhereshallbe improvementof the lowergroundofgravity-typebreakwaters, revetments,quaywalls,andsimilarstructures.

[2] Basic Concept

(1)TheSCPmethodforcohesivesoilgroundisamethodinwhichcasingpipesaredriventotherequireddepthataconstantintervalincohesivesoilground,andthegroundiscompactedandsandpilesareconstructedsimultaneouslywiththedischargeofsandintothegroundfrominsidethecasingpipes.Asfeaturesoftheimprovedsubsoil,thesoilisaffectedinacomplexmannerby(a)thestrengthofthesandpiles,(b)thesandpilereplacementrate,(c)thepositionalrelationshipoftheareaofimprovementtostructures,(d)conditionsrelatedtoactionssuchasintensity,direction,loadingpathandloadingspeed,(e)thestrengthofthegroundbetweenthesandpiles,(f)theconfiningpressureappliedtothesandpilesbythegroundbetweenthepiles,(g)theeffectsofdisturbancesinsideandoutsidetheareaofimprovementbysandpiledriving,(h)thecharacteristicsofthegroundriseatthegroundsurfaceduetosandpiledriving,andwhetherthisriseistobeusedornot.

(2)EffectofExecutionBecausealargequantityofsandpilesaredrivenintothegroundintheSCPmethod,thegroundisforciblypressedout in the horizontal andupwarddirections,whichmay result in disturbance of the ground and reduction ofstrengthintheconstructionareaanditssurroundings.Thisdisplacementoftheground,andspillsofexcesssandinthecasingpipesonthegroundsurface,mayalsocauseaheaveinthegroundsurface.Thus,whenapplyingtheSCPmethod,itisnecessarytoexaminetheeffectofthistypeofgrounddisplacementonneighboringstructures.

(3)PerformanceVerificationMethodMethodsofperformanceverificationof compositegroundcomprising sandpiles and thegroundbetween thepiles include (a) amethod inwhich thecircular slip failure calculationmethod is appliedwith correspondingchangesusing,asabase,anevaluationequationformeanshearstrengthmodifiedtoreflectthecharacteristicsofthecompositeground,and(b)amethodinwhichthecompositegroundisdividedforconvenienceintoapartthatbehavesassandygroundandapartthatbehavesascohesivesoilground,andtheactionsareredistributedsothatthesafetyoftherespectivepartsagainstcircularslipfailureagrees.99),100)Atpresent,theperformanceverificationbytheformermethodisthegeneralpractice.

4.10.2 Sand Piles

(1) Materialsforsandpileshouldhavehighpermeability,lowfinescontentoflessthan75µ m,well-gradedgrainsizedistribution,easeofcompaction,andsufficientstrengthaswellaseaseofdischargeoutofcasing.Whenthesandpileswithalowreplacementarearatioarepositivelyexpectedtofunctionasdrainpilestoaccelerateconsolidationofcohesivesoillayer,thepermeabilityofthesandpilematerialandpreventionofcloggingareimportant.Thepermeabilityrequirementisrelativelylessimportantinthecaseofimprovementwithahighreplacementratio,that is close to the sand replacement. Therefore,materials for sand pile need to be selected considering thereplacementratioandthepurposeofimprovement.

(2)Therearenoparticularspecificationsonmaterialstobeusedforthesandpiles.Anysandmaterialthatcanbesuppliednearthesitemaybeusedfromtheeconomicalviewpointasfarasitsatisfiestherequirements. Fig. 4.10.1 showsseveralexamplesofsandsusedinthepast.Recently,sandwithaslightlyhigherfinescontenthaveoftenbeenused.

–534–


90

0.075 0.42 2.0 5.0 20.0

10203040

50

6070

80

0.01 0.05 0.1 1.0 5.0 10.0 50.00.5(0.075) (0.25) (0.42) (2.0) (9.52)

Pass

ing

wei

ght p

erce

ntag

e (%

)

Grain size (mm)

Case1

Case2Case2

Case3Case3

Case4

Case5

Silt Fine sand Coarse sand Mediumgravel

Finegravel Coarse gravel

Fig. 4.10.1 Examples of Grain Size Distribution of Sands Used for Sand Compaction Piles

4.10.3 Cohesive Soil Ground

(1)EstimationofAmountofGroundHeave

① Theamountofgroundheaveaccompanyingsandpiledrivingisaffectedbyalargenumberoffactors,includingconditions related to the original subsoil, the replacement ratio, conditions related to execution. Therefore,severalestimationmethodsusingstatisticaltreatmentoftheexistingmeasureddatahavebeenproposed.107),108),109)ShiomiandKawamoto107)proposedequation (4.10.1) ,definingtheratiooftheamountofgroundheavetothedesignsupplyofsandpilesasthegroundheaveratioμ.

(4.10.1)where

as :replacementratio L :meanlengthofsandpiles(m) V :groundheave(m3) Vs :designsandsupply(m3) μ :groundheaveratio

② Equation (4.10.1)wasobtainedbymultipleregressionanalysisof28examplesofexecutionwith6m≤L≤20m,adding supplementarydataon six sites, including twoexamplesof sandpileswith lengthsof21mandoneexampleofalengthof25.5m.Asaresultoftheanalysis,itwasfoundthatthecontributionratiotoμdecreasesintheorderof1/L,as,qu,thelowestcontributionratiobeingthatofqu,namelyunconfinedcompressivestrengthoforiginalsubsoil.

(2)PhysicalPropertiesandStrengthEvaluationofHeavedSoilConventionally,thereweremanycasesinwhichgroundheavewasremoved.Recently,however,groundheavehasbeeneffectivelyutilizedaspartofthefoundationgroundinanincreasingnumberofcases.Insuchcases,itisnecessarytoinvestigatethephysicalpropertiesandstrengthoftheheavedsoil. Wherethephysicalpropertiesofheavedsoilduetodrivingofsandpilesareconcerned,anexample114)hasbeenreportedinwhichtheoriginalsubsoilwasimprovedatareplacementrateof70%,andtheheavedsoilportionwasimprovedsoastohaveareplacementratioof40%withø1.2mdiameterofsanddrainpilesdriveninsquarearrangementof1.7mintervalswiththesameconstructionequipmentwithoutcompaction.LoosesandpileswiththemeanN-valueof3.6hadbeenformedintheheavedsoilarea,andtheheightoftheheavedsoilintheareaofimprovementwas3-4m.Testsofthisheavedsoilimmediatelyaftersandpiledrivingrevealedthatthephysical


–535–

propertiessuchasunitweight,moisturecontent,andgrainsizecompositionoftheheavedsoilweresubstantiallyunchangedfromthoseoftheoriginalsubsoiltoadepthequivalenttotheheightoftheheavedsoil.Table 4.10.1 110)showstheresultsofacomparisonoftheunconfinedcompressivestrengthquoftheheavedsoilandqu0asthemeanvalueoftheunconfinedcompressivestrengthbeforeimprovementoftheoriginalsubsoildowntoadepthequaltotheheightoftheheavedsoil.Inthetable,thestrengthofheavedsoiloutsidetheareaofimprovementisshownseparatelyintocaseswithintherangeof45ºor60ºfromthebottomendofthesandcompactionpiles.Thestrengthoftheheavedsoilintheimprovedareashowedastrengthdecreaseofapproximately50%duetodrivingofthesandpiles,butrecoveredtotheoriginallevelin1.5-3.5months.Thestrengthreductionoftheheavedsoiloutsidetheimprovedareawasreportedly30-40%,andrecoverywasslow,requiring8monthsafterpiledrivingforattaintheoriginalsubsoillevel. Forthefinalshapeandphysicalpropertiesofheavedsoilincaseofcompactingintheheavedsoil,thereportbyFukuteet al.109)providesausefulinformation.

Table 4.10.1 Strength Reduction and Recovery in Heaved Soil 110)

Beforeconstruction Immediatelyafterconstruction

1.5-3.5monthsafterconstruction

qu /qu0

InimprovedareaOutsideimprovedarea(45º)Outsideimprovedarea(60º)

1.001.001.00

0.460.620.72

0.930.650.72

4.10.4 Formula for Shear Strength of Improved Subsoil

(1) Severalformulaehavebeenproposedforcalculationoftheshearstrengthofimprovedsubsoilwhichiscompositegroundcomprisingsandpilesandsoftcohesivesoil.99)However,equation (4.10.2)isthemostcommonlyused,irrespectiveofthereplacementratio(see Fig. 4.10.2).Whenas≥0.7,therearemanycasesinwhichthefirstterminequation(4.10.2)isignored,andthewholeareaofimprovementisevaluatedasuniformsandysoilwithø=30º,disregardingequation (4.10.2).

SandpileSandpile

Cohesivesoil

Slip line

Fig. 4.10.2 Shear Strength of Composite Ground

(4.10.2)

where as :replacementratioofsandpile=(areaofonesandpile)/(effectivecross-sectionalareagoverned

bysandpile) c0 :undrainedshearstrengthoforiginalsubsoil,whenz=0(kN/m2)

c0+kz :undrainedshearstrengthoforiginalsubsoil(kN/m2) k :increaseratioinstrengthoforiginalsubsoilindepthdirection(kN/m3) n :stresssharingratio(n = Δσ s Δσ c ) U :averagedegreeofconsolidation

–536–


z :verticalcoordinate(m) τ :averageshearstrengthdemonstratedatpositionofslipfailuresurface(kN/m2)

μs :stressconcentrationcoefficientonsandpile(μs =Δσs Δσz =n/{1+(n −1)as})

μc :stressreductioncoefficientofclaypart(μc =Δσc/ Δσz =1/{1+(n −1)as}) ws :unitweightofsandpile,whensubmerged,unitweightinwater(kN/m3) φs :angleofshearresistanceofsandpile(º) θ :angleofslipfailuresurfacetohorizontal(º)Δσz :meanincrementofverticalstressactingatpositionofobjectslipfailuresurface(kN/m2)Δσs :incrementofverticalstressactingatsandpileatpositionofobjectslipfailuresurface(kN/m2)Δσc :incrementofverticalstressactingatcohesivesoilbetweensandpilesatpositionofobjectslip

failuresurface(kN/m2)Δc/Δp :strengthincreaseratiooforiginalsubsoil

(2)ConstantsusedinPerformanceVerificationInthepastexamplesofperformanceverification,theconstantsusedinequation (4.10.2)variedoverawiderange.Thevaluesof theconstantsused in theperformanceverificationshouldbesetconsidering thestrengthof theoriginalsubsoil,theapplicablemarginofsafety,themethodofperformanceverificationtobeused(see4.10.6 Performance Verification),andthespeedofconstruction.Thestandardvaluesofthestresssharingratioandtheangleofshearresistanceobtainedfrompastexamplesusingequation (4.10.2)areasfollows:

as≤0.4 n=3 φ=30º0.4≤as≤0.7 n=2 φs=30º-35ºas≥0.7 n=1 φs=35º

Inrecentyears,thenumberofexamplesinwhichslagandsimilarmaterialswereusedasmaterialsforsandpileshasincreased.Slagincludematerialswhichcanbeexpectedtohavecomparativelyhighanglesofshearresistance.Whensuchmaterialsaretobeused,performanceverificationmaybeperformedusinganangleofshearresistanceclosetothemeasuredvalue,providedadequatecautionisusedinsettingthestresssharingratio.

(3)ClassificationofShearStrengthFormulaeofCompositeGroundInthepastexamplesofperformanceverification,inadditiontoequation (4.10.2),thefollowingthreeequationsareused.115)Equation (4.10.4)andequation(4.10.5)arethoseproposedasequationsforshearstrengthofcompositegroundwithhighreplacementratios. Accordingto theexistingsurveyresults,99)with lowreplacementratiosofas≤0.4,almostallexamplesofperformanceverificationusedequation (4.10.2),andveryfewexamplesusedequation (4.10.3).Similarly,when0.4≤as≤0.6,themajorityofexamplesusedequation (4.10.2),andexamplesusingequation (4.10.4)accountedforonlyabout1/5ofthetotal.When0.6<as,equation (4.10.4)andequation(4.10.5)werefrequentlyused.

(4.10.3) (4.10.4)

(4.10.5)

Here,thedefinitionsofsymbolsintheaboveequationswhicharedifferentfromthoseinequation(4.10.2) areasfollows.

wm :meanunitweight(wm = wsas + wc (1− as ) wc :unitweightofcohesivesoil,whensubmerged,unitweightinwater(kN/m3) φm :meanangleofshearresistancewhenimprovedsubsoilwithheightreplacementratioisassumed

tobeuniformsubsoilφm=tan–1(μsastanφs)

4.10.5 Actions

(1)The displacement of the main body during earthquake with subsoil improved by the sand compaction pilemethod tends to be reduced. When setting the seismic coefficient for verification of themain body in caseofsoil improvementby thesandcompactionpilemethod, it ispossible tosetarationalseismiccoefficientbyappropriatelyevaluatingthisreductioneffect.Forthebasicflowanditemsrequiringcautionwhencalculatingtheseismiccoefficientforverification, Chapter 5, 2.2.2(1) Seismic coefficient for verification used in verification of damage due to sliding and overturning of wall body and insufficient bearing capacity of foundation ground in variable situations in respect of Level 1 earthquake ground motioncanbeusedasareference.


–537–

Thecharacteristicvalueoftheseismiccoefficientforverificationofgravity-typequaywallsinthecaseofsoilimprovementbythesandcompactionpilemethodwithareplacementratioof70%ormorecanbecalculatedusingequation (4.10.6)bymultiplyingthemaximumvalueofcorrectedaccelerationobtainedfortheunimprovedsoilbyareductioncoefficient.Incalculatingthemaximumvalueofcorrectedaccelerationfortheunimprovedsoil,this part, Chapter 5, 2.2.2 (1) Seismic coefficient for verification used in verification of damage due to sliding and overturning of wall body and insufficient bearing capacity of foundation ground in variable situations in respect of Level 1 earthquake ground motion canbeusedasareference.Itshouldbenotedthatthisreductioncoefficientwasobtainedbasedona2-dimensionalnonlineareffectivestressanalysisforunimprovedsubsoilandimprovedsubsoilwitha70%replacementratioforgravity-typequaywalls.

(4.10.6)where

kh’ :characteristicvalueofseismiccoefficientforverification αc :maximumvalueofcorrectedacceleration(cm/s2) g :gravitationalacceleration(=980cm/s2) Da :allowabledeformation(cm)(=10cm) Dr :standarddeformation(cm)(=10cm) c :reductioncoefficientofseismiccharacteristicsduetoimprovedsubsoil(c=0.75)

4.10.6 Performance Verification

(1)ExaminationofCircularSlipFailure

① ThemodifiedFelleniusmethodisfrequentlyusedincircularslipfailurecalculationsinperformanceverificationofimprovedsubsoilbythesandcompactionpilemethod.IncircularslipfailurecalculationsbythemodifiedFelleniusmethod,thesubsoilandsuperstructuresaredividedintoseveralsegmentscalledslices,andthenormalstressontheslipsurfaceiscalculatedignoringthestaticallyindeterminateforcesactingbetweenslices.Thatis,onlyactionsactingontheoriginalsubsoilincludedinasliceportionareassumedtocontributetothenormalstressontheslipsurfaceofthatslice.Hereinafter,thisnormalcalculationmethodiscalledthe“slicemethod”.Ontheotherhand,inactualsubsoil,loadsaredistributedinthegroundtoacertainextent.Inordertoreflecttheeffectsofthisstressdistributioninslipfailurecalculations,thereisamethodthattheverticalstressincrementΔσz atanarbitrarypointonaslipsurfaceobtainedusingBoussinesq’sequationappliestothemodifiedFelleniusmethod.Hereafter,thisiscalledthe“stressdistributionmethod”.

② Intheperformanceverificationofimprovedsubsoilbythesandcompactionpilemethod,eithertheslicemethodorthestressdistributionmethodcanbeused.Intheexaminationofcircularslipfailure,verificationcanbeperformedusingequation (4.10.7).Inthisequation,thesubscriptddenotesthedesignvalue.

(4.10.7)where

:sumofresistantmoments(kN・N)

r :radiusofslipcircle(m) s :widthofslicesegment(m) θ :angleofslipsurfacetohorizontal(º) :shearstrengthofsubsoil(kN/m2)

:sumofactingmoments(kN・N)

Caseofquaywall:

w' :weightofslicesegment(kN/m) q :surchargeonslicesegment(kN/m) qRWL :buoyancyofslicesegmentduetodifferenceinwaterlevelwhentheresidualwaterlevel,RWL,

atthebacksideoffacilitiesishigherthanthewaterlevel,LWL,atthefrontofthefacilitiesρwg (RWL-LWL)(kN/m)

θ :angleofbottomofslicesegmenttohorizontal(º) x :horizontaldistancebetweencenterofgravityofslicesegmentandcenterofslipfailurecircle(m)

–538–


Caseofbreakwater:

w' : weightofslicesegment(kN/m)q : spatially-distributed load of breakwater acting on slice segment when effective weight of breakwaterisdividedbyitswidth(kN/m)θ : angleofbottomofslicesegmenttohorizontal(º)

Incalculatingthedesignvaluesintheequation,Chapter 5, 2.2.3 (5) Examination of Sliding Failure of Ground in Permanent Situationcanbeusedasareferenceforquaywalls,and Chapter 4, 3.1.4 (5) Examination for Slip of Groundcanbeusedforbreakwaters. Theshearstrengthoftheimprovedsubsoilcanbecalculatedbyequations (4.10.2) to(4.10.5),dependingonthedesignconditions.Forexample,whenusingequation (4.10.2),thedesignvalueoftheshearstrengthoftheimprovedsubsoilcanbecalculatedbythefollowingequation.Inthiscase,ΔσzisobtainedusingBoussinesq’sequation.

(4.10.8)

Thedesignvaluesintheequationcanbecalculatedusingthefollowingequations.Thesubscriptkdenotesthecharacteristicvalue.Forsymbols,etc.,equation (4.10.2)canbeusedasareference.

③Fig. 4.10.3showsaschematicdiagramofcircularslipfailure.

x

r

w

s

SCP improved subsoil

θ τ

Fig. 4.10.3 Schematic Diagram of Circular Slip Failure

④ Forpartialfactorsforuseintheexaminationofcircularslipfailureofimprovedsubsoilwhensoilimprovementisconductedbythesandcompactionpilemethodwithreplacementratiosof30%to80%,thevaluesshowninTable 4.10.2canbeusedasareference116).Inthiscase,cautionisnecessary,asthepartialfactorsforcircularslipfailureshownin3.2.1 Stability Analysis by Circular Slip Failure Surfacecannotbeused.InsettingthepartialfactorsinTable 4.10.2,thecaseinwhichtheslipcirclesurfacepassesthroughsandysubsoildeeperthantheimprovedsubsoilisnotexamined.Therefore,insuchcases,separatestudybyanappropriatemethodisnecessary.


–539–

Table 4.10.2 Standard Partial Factors

(a) Permanent situation (high earthquake-resistance facilities)

Highearthquake-resistancefacilitiesStandardreliabilityindexβT 3.1

Reliabilityindexβusedincalculationofγ 3.1γ α µ/Xk V

Circularslipfailure

γc ' Cohesion Landfillsoil 1.00 0.001 1.00 0.10Originalcohesivesubsoil 0.95 0.092 1.00 0.10

γtanφ ' Tangentofshearresistance

Mound,backfillingstones,etc. 0.95 0.218 1.00 0.10

SCPtanφs'=0.70 0.80 0.861 1.00 0.05γwi Ground,caisson,etc.abovelevelofseabottom 1.00 –0.041 0.98 0.03

Mound,backfillingstones,etc. 1.05 –0.041 1.02 0.03Sandysoilbelowseabottom(SCP) 1.00 0.069 1.00 0.03Cohesivesoilbelowseabottom 1.00 0.009 1.00 0.03

γq Surcharge 1.35 –0.270 1.00 0.40γRWL Residualwaterlevel 1.00 –0.022 1.00 0.05

(b) Permanent situation (revetments and quaywalls)

OthersStandardreliabilityindexβT 2.7


Circularslipfailure

γc ' Cohesion Landfillsoil 1.00 0.001 1.00 0.10Originalcohesivesoil 1.00 0.092 1.00 0.10

γtanφ ' Tangentofshearresistance


SCPtanφs'=0.70 0.80 0.861 1.00 0.05γwi Ground,caisson,etc.abovelevelofseabottom 1.00 –0.041 0.98 0.03

Mound,backfillingstones,etc. 1.00 –0.041 1.02 0.03Sandysoilbelowseabottom(SCP) 1.00 0.069 1.00 0.03Cohesivesoilbelowseabottom 1.00 0.009 1.00 0.03

γq Surcharge 1.30 –0.270 1.00 0.40γRWL Residualwaterlevel 1.00 –0.022 1.00 0.05

–540–


(c) Permanent situation (breakwaters)

BreakwaterStandardreliabilityindexβT 3.3


Circularslipfailure

γc ' Cohesion Originalcohesivesoil 0.90 0.484 1.00 0.10γtanφ '

Tangentofshearresistance


SCPtanφs'=0.70 0.90 0.664 1.00 0.05γwi Wave-dissipatingworks,footprotectionworks,etc.

aboveseabottom 1.05 –0.140 1.02 0.03

Mound 1.05 –0.140 1.02 0.03Sandysoilbelowseabottom(SCP) 1.00 –0.110 1.00 0.03Cohesivesoilbelowseabottom 1.00 0.115 1.00 0.03

γq Distributedload(weightofcaissons) 1.00 –0.140 0.98 0.02

(2)ExaminationofConsolidation

① CalculationofconsolidationInperformanceverificationofsettlement,equation (4.10.9)canbeused.

(4.10.9)

where

Cc :compressionindex h :heightofembankment(m) H :thicknessofconsolidationlayer(m) mv :coefficientofvolumecompressibility(m2/kN) p’ :consolidationpressure(kN/m2) p0’ :initialpressure(verticalpressurebeforeconstruction)(kN/m2) pc’ :preconsolidationpressure(kN/m2) Sa :allowableresidualsettlement(m) U :consolidationrate e0 :initialvoidratiooforiginalsubsoil α :coefficientofstressdistribution(ratioofdistributedstressinsubsoilandconsolidationpressure

orembankmentpressure) β :settlementreductionratio(ratioofsettlementofcompositegroundandsettlementofunimproved

subsoil) γ’ :effectiveunitweightofembankment(kN/m3) Δe :reductionofvoidratiooforiginalsubsoil Sf0 :settlementwithoutimprovement Sf :residualsettlement

② ComparisonofcalculatedsettlementandmeasuredvaluesTheresidualsettlementofimprovedsubsoilisobtainedbymultiplyingthepredictedsettlementofunimprovedsubsoilbythesettlementreductionratioβasshowninequation (4.10.9).Thesettlementreductionratioβisgenerallyexpressedinaformsimilartothestressreductioncoefficientμc.AnexampleofacomparisonofthecalculatedsettlementreductionratioandmeasuredvaluesisshowninFig. 4.10.4.Here,thevaluesofβonthey-axiswereobtainedbyestimatingthefinalsettlementoftheimprovedsubsoilbyapproximatingtheprogressofmeasuredsettlementovertimeasahyperbola,andestimatingtheratiotothecalculatedfinalsettlementoftheoriginalground.TheFigurealsoshowsthesettlementreductionratio(β =1–as)whichisusedempirically


–541–

withhighreplacementratiosandsettlementreductionratiosforstresssharingratiosofn=3,4,and5.Fromthisfigure,itcanbeunderstoodthatthereductionofsettlementduetoimprovementislarge,thiseffectisinfluencedbythereplacementratio,andalthoughvariationsinthemeasuredvaluesarelarge,thevaluesareclosetothosecalculatedassumingastresssharingratioofapproximately4.

β = 1+(n-1)as1

0

0.2

0.4

0.6

0.8

1.0

0.0 0.2 0.4 0.6 0.8 1.0Replacement area ratio as

n = 4

n = 5

n = 3

Settl

emen

t rat

io β

Marine constructionLand construction

Fig. 4.10.4 Relationship between Settlement Reduction Ratio and Replacement Rate 109)

③ ComparisonbetweencalculatedandmeasuredconsolidationtimeTheconsolidationrateofsubsoilimprovedbythesandcompactionpilemethodtendstobedelayedcomparedto that predicted by Barron’s equation. Fig. 4.10.5 based on previous construction data shows the delay inconsolidationintermsofthecoefficientofconsolidationasamajorparameter.Inthefigure,Cv isthecoefficientofconsolidationreverse-analyzedfromactualmeasurementsforthetime-settlementrelationship,andCv0isthecoefficientofconsolidationobtainedfromlaboratorytests. Itcanbeseenthatthetimedelayinconsolidationbecomesgreaterwiththeincreaseinthereplacementarearatio.

Replacement rate as

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.1

0.2

0.5

1.0

Cvp

/ Cv 0

Cvp

Cv0

::

The coefficient of consolidation from actual measurementsThe coefficient of consolidation obtained from laboratory tests

Land constructinMarine constructin

Fig. 4.10.5 Delay in Consolidation of Subsoil Improved by Sand Compaction Pile Method

④ ComparisonofcalculatedandmeasuredstrengthincrementsTheincrementofstrengthofclaybetweensandpilesΔccanbecalculatedusingequation(4.10.10). Ontheotherhand,theresultsofareversecalculationofμcfromthemeasuredvaluesofthestrengthincrementofclaybetweensandpilesareshowninFig. 4.10.627).They-axisinthefigureexpressestheratio(μc(Δca/Δcc))ofthemeasuredvaluesΔcaofthestrengthincrementinimprovedsubsoilbythesandcompactionpilemethodtothe

–542–


predictedvaluesΔcc(=ΔσzΔc /ΔpU)ofthestrengthinunimprovedsubsoil.Themeasuredvaluesofthestrengthincrementvary,centeringaroundstresssharingration=3–4.

(4.10.10)

where μc :stressreductioncoefficientofcohesivesubsoilportion(μc =ΔσcΔσz =1{1+(n−1)as}) Δσz :meanvalueofverticalstressincrementduetoactionatobjectdepth(kN/m2)

Δc/Δp :strengthincreaserateoforiginalcohesivesubsoil U :meandegreeofconsolidation

0

0.2

0.4

0.6

0.8

1.0

0.0 0.1 0.2 0.4 0.6 0.70.3 0.5

　 c(

) cc

c a/ Kasai-oki

Replacement area ratio as

n = 1

n=6

n=4n=4

n=3

n=2

: calculated increase of cohesion=c/p s z・U: increase of cohesion based on surveys before and after construction

LandOffshore

cc

ca

μ

Fig. 4.10.6 Strength Increase of Cohesive Soil between Sand Piles in Improved Subsoil 109)

4.11 Rod Compaction Method4.11.1 Basic Policy of Performance Verification

Intherodcompactionmethod,itisnecessarytoconductperformanceverificationappropriatelybasedontheactualrecordsofthepastexecutionortheresultoftestexecutionadequatelyconsideringthecharacteristicsoftheobjectgroundandthecharacteristicsoftheexecutionmethod.


Because this improvement method is a method of compaction employing only vibration, its effect decreasesexponentiallywithdistance.Accordingly,itispreferabletodeterminethearrangementandspacingofthevibratoryrodsbasedontherelationshipbetweenthepitchofthevibratoryrodsobtainedfromthepastexamplesortestexecutionandtheN-valueafterexecution.Inapplicationtotheexistingsheetpilequaywalls,thespacingofthetierodsshouldbeconsideredwhendeterminingthespacinginthedirectionofthefacelineofthequaywall.

4.12 Vibro-fl otation Method4.12.1 Basic Policy of Performance Verification

Inthevibro-flotationmethod,itisnecessarytoconductperformanceverificationappropriatelybasedontheactualrecordsofthepastexecutionortheresultoftestexecution,adequatelyconsideringthecharacteristicsoftheobjectgroundandthecharacteristicsoftheexecutionmethod.


[1] Examination using Past Results of Execution

(1)Whensufficientlyreliablepastresultssuchasthecharacteristicsoftheobjectground,piledrivingdensityinthevibro-flotationmethod,capacityofthevibro-float,andcorrelationwiththeN-valuesofthegroundbeforeandafter


–543–

improvementareavailable,theperformanceverificationoftheimprovementworkscanbeconductedbasedonthis.

(2)The limitsofapplicabilityof thevibro-flotationmethodestimatedfromtheexamplesofexecution todateareasshowninFig. 4.12.2125).Fig. 4.12.2ispreparedbasedonthemeasuredvaluesof11examplesofexecutionusingsquareandequilateraltriangularpatternswithpilespacingsof1.2-1.5m,togetherwithotherexamplesofexecution,andcanbeusedasaroughestimateofthelimitsofapplicabilityofthismethod.

0

20

40

60

80

0.02

100

0.01 0.03 0.05 0.07 0.1 0.2 0.3 0.5 1.0 2.0 3.0 5.0

Grain size (mm)

N min=8-15

Silt Fine sand Coarse sand GravelPe

rcen

tage

pas

sing

by

mas

s (%

)

Limit o

f effe

ctiven

ess of

vibro-

floata

tion m

ethod

N min=15-20N min=15-20N min=20-15N min=20-15

Min

imum

gra

in si

ze di

stribu

tion

pref

erab

le as

mak

eup m

ateria

l

Fig. 4.12.2 Relationship between Grain Size of Original Subsoil and Minimum N-value after Compaction (Case of Sandy Soil)

4.13 Drain Method as Liquefaction Countermeasure WorksIn the drain method as liquefaction countermeasure works, drains using materials with good permeability areperformedingroundwherethereisapossibilityofliquefaction.Thesedrainsreducethedegreeofliquefactionbyincreasing thepermeabilityof thegroundasawhole. Drainsare frequentlyperformed inapile shape;however,wall shapeddrains and shapeswhich surround the structure have also been considered. If amaterialwith goodpermeability,suchassandinvasionpreventionsheets,isusedinbackfillingofquaywalls,thiscanalsobeconsideredakindofdrain.Crushedstoneorgravelisfrequentlyusedasdrainmaterial.Recently,however,perforatedpipesofsyntheticresinandsimilarproductshavebeendeveloped.Inshort,asindicatedabove,avarietyofdrainmethodsareusedasliquefactioncountermeasureworks.

4.14 Well Point MethodInsomecases,thewellpointmethodisusedincombinationwiththesanddrainmethodorplasticboarddrainmethodinordertoincreaseeffectiveweightofground.Frequently,however,itisusedforthepurposeofreducingthewaterlevelinsandorsandysiltstrata,therebyhelpingdryworkunderthegroundexecution.(Fig. 4.14.1)129).

0.001 0.005 0.01 0.05 0.1 0.5 1.0 50

20

40

60

80

100Clay Silt

SandFine sand Coarse sand

Gravel

Vacuumdrainage

Electro-osmosisElectro-osmosis

GravitydrainageGravitydrainage

Wellmethod

Wellmethod

Sumpingmethod

Sumpingmethod

Perc

enta

ge p

assi

ng b

y m

ass (

%)

Grain size (mm)

Vacuum wellmethod

Fig. 4.14.1 Applicability of Methods in respect of Soil Grain Size

–544–


4.15 Surface Soil Stabilization MethodSurface soil stabilization methods are widely used for purposes such as securing trafficability for constructionequipmentinadvanceofactualsoilimprovementandincreasingthebearingcapacityofextremelysoftsubsoil,forexample, in reclaimed landwhich has been reclaimedusing soft cohesive or extremely soft cohesive soil, and topreventresidentsfromfallingintothereclaimedland,preventfoulodors,preventbreedingofdisease-bearinginsectsinstandingwater,andsealharmfulindustrialwastesinreclaimedlandnearresidentialareas.130),131)

4.16 Liquefaction Countermeasure Works by Chemical Grouting Methods 4.16.1 Basic Policy of Performance Verification

(1)Thefollowingdescribesthemethodofperformanceverificationwhenusingchemicalgroutingmethodsforthepurposeofliquefactioncountermeasureworks.Asgroutingmethodsforliquefactioncountermeasureworks,thepermeationgroutingmethod,multiplepermeationgroutingmethod,groutingmethod,andothershavebeendeveloped.132),133),134)

(2)Regarding applicable soil quality, basedonpast records, it canbe assumed that thefines content generallycomprisesnomorethan40%ofthesubsoil.

(3)Intheexaminationofstabilityagainstcircularslipfailuresafetysideexaminationresultsshouldbeadoptedbyevaluatingtheimprovedsubsoilascmaterialorc–ømaterial.

(4)Asaguideline, the improvedstrength forpreventing liquefactionof soilwith solution-typechemicals is anunconfinedcompressivestrengthof80–100kN/m2.ThisimprovedstrengthisequivalenttoahighliquefactionresistanceontheorderofRL20=0.4ofcyclicshearingstressratiointhecyclicundrainedtriaxialtest.Here,soilimprovedbysolution-typechemicalgrout,evenwhenitsunconfinedcompressivestrengthis100kN/m2,isnotalwaysregardedasamaterialwhichdoesnotliquefyduetosuchasitsdeformationcharacteristicundercyclicmotions.Therefore,itisnecessarytospecifytheimprovedstrengthbycalculatingactionsinaccordancewiththeperformancecriteriaofthefacilities.Onthecontrary,evenwithverylowimprovedstrength,suchasanunconfinedcompressivestrengthoftheorderof16kN/m2,ithasbeenreportedthatdilatancycharacteristicschangefromlooselyfilledsandtodensesand,inthatfluidliquefactionlikethatinloosesandisnotobserved,andliquefactionpotentialisgreatlyimproved.

4.16.2 Setting of Improvement Ratio

Inprinciple, the improvement ratio shall be100%,namely the entire area subject to the improvement shall beimproved.Incaseswheretheimprovementratioistobereduced,acarefulexaminationshouldbemade,forexample,byconfirmingthatsettlementanddeformationwhicharedetrimentaltofacilitieswillnotoccurbyconductingmodeltests,etc.

4.17 Pneumatic Flow Mixing Method4.17.1 Basic Policy of Performance Verification

(1) Itisnecessarytoconductperformanceverificationofthepneumaticflowmixingmethodbyappropriatelysettingthenecessarystrengthofthetreatedsubsoil,areaofimprovement,etc.basedonsurveysandtestresultsofthesoilwhichistobeimproved,andthestabilizedsoil,andtheconditionsofapplication.

(2)Inthepneumaticflowmixingmethod,stabilizerisaddedtothesoilbeingimproved,forexample,dredgedsoil,duringpneumatictransportation.Theobjectsoilandstabilizeraremixedusingtheturbulenceeffectoftheplugflowgeneratedinthetransportpipe,andthemixtureisthenplacedatthedesignatedlocation.Fortheprincipleandfeaturesofthisexecutionmethod,Manual on Pneumatic Flow Mixing Technology 135),136)canbeusedasareference.


–545–

4.18 Active Earth Pressure of Geotechnical Materials Treated with Stabilizer4.18.1 General

(1)Thissectiondescribes fundamentalsofperformanceverification forcalculationofactiveearthpressurewhenusinggeotechnicalmaterialssolidifiedbystabilizerssuchascementasbackfillmaterials. Solidifyingagentsconsideredinthissectionincludethosethathardennaturallyandothersthatarehardenedartificiallybyaddingcementorotherstabilizer. Materialsdevelopedtodatearelistedbelow. Thevarietyofmaterialstendtoincreaseinfuture.

① Premixedsoil(treatedsoilbypremixingmethod)② Lightweighttreatedsoil③ Cement-mixedsoilsotherthantheabovetwo④ Solidifiedcoalash⑤ Self-hardeningcoalash⑥ Blastfurnacegranulatedslagusedforsolidifying

4.18.2 Active Earth Pressure

[1] Outline

(1)Whenusingsolidifiedgeotechnicalmaterials,thematerialpropertiesandthecharacteristicsofearthquakemotionshouldbeappropriatelytakenaccountincalculationsofactiveearthpressureonastructure.

(2)When calculating active earth pressure during an earthquake, the seismic coefficient methodmay generallybe used. When detailed examination of earth pressure during an earthquake is required, however, responseanalysisandothersmustbecarriedout.Methodstocalculateearthpressureusingtheseismiccoefficientmethodconsideringmaterialpropertiesaredescribedin4.18.2 [2] Strength Constants.

(3)Generally,whensolidifyingagentsarejudgedtohavesufficientlylargecohesion,liquefactioninthetreatedareaneednotbeconsidered.Althoughdependingonactionsduetogroundmotion,iftheunconfinedcompressivestrengthquisgreaterthanapproximately50–100kN/m2,excessporewaterpressureintheareaofimprovementduringactionofgroundmotionmaybeignored.

[2] Strength Constants

Themethodofdeterminingstrengthconstantsforgeotechnicalmaterialswilldifferdependingonthematerialused.Itisnecessarytoconsidercohesionandtheangleofshearresistanceinaccordancewiththepropertiesoftherespectivematerialsused.Ingeneral,deepmixedsoil,lightweighttreatedsoil,andsoilsolidifiedwithcoalashareassumedtobecmaterials.Premixedsoilcanbeconsideredtobeamaterialofboththecandøtype.Granulatedslagisusuallytreatedasømaterial,butitmayalsobetreatedasacmaterialincaseswhereitssolidificationpropertyispositivelyemployed.

[3] Calculation of Active Earth Pressure

(1)Generally,theearthpressuremaybeevaluatedbasedontheprovisionsinPart II, Chapter 5, 1 Earth Pressure.TheprincipleforcalculationofearthpressuremaybethesameastheMononobe-Okabeprinciple.Inthismethod,theearthpressureiscalculatedbyanequilibriumofforcesinaccordancewithCoulomb’sconceptofearthpressurebyassumingthatthesubsoilfailswhileformingawedge.

(2)Manyfactorsremainunknownabouttheearthpressureduringanearthquake.Thisisparticularlysignificantontheearthpressureduringanearthquakeinsubmergedsubsoils.Nevertheless,theprincipleofearthpressureinPart II, Chapter 5, 1 Earth Pressure hassofarbeenadoptedintheperformanceverificationofmanystructureswithsatisfactoryresults.

(3)Equation(4.18.1),anexpansionoftheearthpressureequationinPart II, Chapter 5, 1 Earth Pressure,canbeappliedtomaterialshavingboththecohesionc andangleofshearresistanceφ(seeFig. 4.18.1).

–546–


(4.18.1)

where pai : activeearthpressureintensityactingonwallbythei-thlayer(kN/m2) ci : cohesionofsoilinthei-thlayer(kN/m2) φi : angleofshearresistanceinthei-thlayer(°) γi : unitweightofthei-thlayer(kN/m3) hi : thicknessofthei-thlayer(m) ψ : angleofwalltothevertical(°) β : angleofgroundsurfacetothehorizontal(°) δ : angleofwallfriction(°) ζi : angleoffailuresurfaceofthei-thlayertothehorizontal(°) ω : surchargeperunitareaofgroundsurface(kN/m2) θ : resultantseismicangle(°)θ=tan–1korθ=tan–1k' k : seismiccoefficient k' : apparentseismiccoefficient

hi

h1

h2Pi-1

Pih

Piv Pi

Pi

P1

P2

1

2

i

+8)(

ξ

ξ

ξ

δ

ψ

β

ω

Fig. 4.18.1 Earth Pressure

(4)Equation (4.18.1) is an extensionofOkabe’s equation.142) This extension lacks such rigorousness thatOkabesolvedtheequilibriumofforces. However,whenthesoil isexclusivelygranularmaterialwithnocohesionorexclusivelycohesivematerialwithnoangleofshearresistanceφ,itisconsistentwiththeequationsinPart II, Chapter 5, 1 Earth Pressure.


–547–

(5)Theearthpressureandtheangleoffailuresurfaceshouldbecalculatedseparatelyateachsoillayerwithdifferentsoilproperties,whiletheearthpressuredistributionandthefailurelineinsideeachlayeraretreatedaslinear.Actuallywithinasoillayer,theearthpressureandthefailurelinesometimesbecomecurvedwhencalculatedfordividedsublayers.ThiscontradictstheoriginalassumptioninOkabe’sequationthatisbasedonalinearsliponthepremiseofCoulomb’searthpressure.

(6)Whenusingtheequationsabove,theexistenceofcrackssometimeshastobeconsideredinaccordancewiththecharacteristicsofthegeotechnicalmaterialsused.

[4] Cases where Improvement Width is Limited

WhentheareatreatedwithsolidifiedgeotechnicalmaterialsislimitedandMononobe-Okabe’sequationcannotbeappliedsimply,theearthpressureisevaluatedbyasuitablemethodthatallowstheinfluenceofthetreatedareatobeassessed.Whenthetreatedareaislimited,theearthpressurecanbeevaluatedbytheslicemethod143).

①Withtheslicemethod,threemodesoffailureareexamined(seeFig. 4.18.2).

② TheearthpressuredistributioniscalculatedbyassumingthatthedifferencebetweentheresultantearthpressuresatadjacentdepthsistheearthpressureintensityforthecorrespondingdepthMode1:whenauniformslipsurfaceisformedinthewholebackfill(shearresistancemode)Mode2:whenacracksdowntothebottomofthesolidifiedsoillayerisdeveloped(crackfailuremode)Mode3:whenaslipsurfaceisformedalongtheedgelineofthesolidifiedrange(frictionresistancemode)Note:AmongMode1,thecaseinwhichtheslipsurfacedoesnotpassthesolidifiedbodyiscategorizedasMode0.

Mode 1Mode 2 Mode 3

Mode 0

Fig. 4.18.2 Three Failure Modes Considered in the Slice Method

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4.6 lightweight treated soil method4.6 lightweight treated soil method (1) definition and outline of...

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