Experimental study on the mechanical behavior of highly structured geomaterials and its modeling

(1)

Title

Experimental study on the mechanical behavior of highly

structured geomaterials and its modeling( 内容の要旨(Summary)

)

Author(s)

SARR AMADOU MOCTAR

Report No.(Doctoral

Degree)

博士(工学) 甲第215号

Issue Date

2004-03-25

Type

博士論文

Version

URL

http://hdl.handle.net/20.500.12099/1936

※この資料の著作権は、各資料の著者・学協会・出版社等に帰属します。

(2)

氏名(本籍) 学位の種類学位授与番号学位授与目付専攻学位論文題目

SARR AMADOU MOCTAR(セネガル) 博士(工学)

甲第 215 号

平成16 年 3 月 25 日生産開発システム工学専攻

Experimentalstudy on the _{mechanicalbehavior} _{of highl}

geomaterials andits modeling

(高位の構造を有する地盤材料の実験とモデル化) 学位論文審査委員 (主査)教授八嶋厚 (副査)教授杉戸真太教授本城勇助教授張鋒

論文内容の要旨

Inordertoaccuratelypredictthemechanicalbehaviorofhighlystructuredgeomat

degradation _efTbct _needs to beincorporatedinto the _constitutive

_{model･′Sir}

geomaterials areinvoIvedin many geotechnicalproblems,SuCh as the bearinl foundationandtheprogressivefailureofslope,muChattentionhastobepaidtot】 behaviorofstruCturedsoils.InordertosoIvetheengIneerlngPrOblemsrelatedtosl withlargenegativedilatancy,itisnecessarytoproposeanappropriateconstitutivem･ intoaccountthee飴ctofthedegradationoFstructuredurlngShearlngPrOCeSS･Inthi elasto-PlasticconstitutivemodelorlglnallyproposedbyAdachiandOkaisextend describethemechanicalbehaviorofhighlystruCturedgeomaterialsbyconsidetingth theoverconsolidationboundarysurfhceduetothedeteriorationofthestruCture･･The theextendedmodelisevaluatedthroughacomparisonbetweensimulatedandexper! ondiatomaceoussoils,tyPICalJapanesea11uvialandPleistocenemarineclaysandsel

rocks.In the&amework ofenglneerlng PrOPerties ofgeomaterials,a teChnica

construCtiononswe11ingsoilsinSenegal(WestA什ica)ispresented･

The content _ofthis _{researcllWOrks} can be dividedinto _{three parts,mainly,}

(3)

(arrangementofparticles)andinterparticlebondingisreportedinawiderangeofliteri

e脆ctsonthemechanicalbehaviorofnatura)geol一一aterials･Laboratorytestswerec

Hiruzenbara diatomaceous _{soils block-SamPIed} at Okayama prefecture,Japz compressiontestswerecarriedoutonthenormallyandoverconsolidatedstates･The<

results show that the structured soilexhibit strain soRenlng Withlarge negative

diffbrentconnningpressLlreSduringshearingprocess･Thepeakstrength,reSidual;

sti肋essincreasewiththeincreaseinthecon爪ningpressure･Itisalsoobservedthat theconnningpressureonthegenerationofporewaterpressureisslgnincantdur process･ThepatternoftheporeYaterPreSSuregenerationdependsonthecon伽i Underlowconnningpressures,theporewaterpressuregenerationreachesapeakbef strengthandthendecreases･Incontrast,thegenerationofporewaterpressureun( conditionincreasesdurlngthestrainsoRenlngPrOCeSS･Theobservednegativedilal strainso鮎nlngprOCeSSCanbemodeledbyintroduclngthedestruCtionofthestru shearlng･AIso,triaxialcompressiontestresultsof職kasudiatomaceousearth,Holo. clayfromHachirogataandUpper･MostPleistocenemarineclay&omT凱IrumiarellSed Thestress-dilatancyrelationsarecarefu11yanalysed･Twostagesareobserヤedinthe thedilatancydurlngShearlng･Thenrststageisadecreaseofthenegativedilatancyas5 anincreaslngStreSSratio･Thesecondstageshowsasmalldecreaseindilatancyand withstressdrop･Thepeakofthedilatancycurvenearlycorrespondstothepeakstr material.Thesoilsexhibitsimultaneouslynegat'ivedilatancyandstrainsoftenlngS･Itj thattheoverconsolidationhistoryhase脆ctsonthedilatancy･Underlowercon伽i-negativedilatancylSeXhibitedatahighlevelofstressratio･Asdeformationprogress

decreases _{and tends} to _zero.The _{e飴ct ofoverconsolidation} _vanished completely structtlredegradesdurlngShearlngPrOCeSS･Whenanultimatestateisachieved,thevo

stoppedwhilethesheardeformationofsoilcontinuesunderconstantVoidratio,aty stateorsoil.

Recently,therehavebeenimportantdevelopmentsinconstitutivemodelsincorporat

ofstructure degradation durlng Shearlng PrOCeSS･In this

_{research,neWlogisti(}

equations,thatbettertakeintoaccountthee触tsofstructuredegradationonth(

behavior,areihtroducedto _{the extended} elasto-Plastic modelproposed byAdac Yhshima.1twasconsideredthedecreaseintheinitialvolumetriccomponentofstressl

andtheshrinkageoftheoverconsolidationboundarysurfhcerelatedtodegradationof ThesampleissupposedtoinitiallybeconsolidatedisotroplCallyuptoacertain

(4)

PrOPOSed by Adachiand Oka,its mod描ed modeIs withlogistic evolutiona]equations and exponentialequations,are uSedtosimuJatethestl･ain soReningwithIargenegativediIatancy

exhibitedduringshearlngprOCeSS･TTheapp]icationofthosemodelsisevaluatedthrougha COmParisonbetweenthesimulatedandtheexpqrimentalresultsonthehighlystructLlredsoils

mentionedabove･Itisfoundthatthbmodi鮎dmodelwithlogisticevolutionaJequationsisthe

mostappropriateonetodescribethestrainso鮎ningbehaviorwithlargenegativedilatancy･ Intheframeworkofproblematic

_{geomateriaIs,aPrOPOSalofaresearchprqjectrelatedto}

SWellingmarlsinSenegal(鴨stA舟ica)ispresentedinthisstudy.MostW由tAfricanareasofhigh

densitiesofpopulationarecoastalordelta･TheyareCOVeredwithrecentdepositsofcompressible CIays,Silts,andmuds･Investigationsonsuchsoilshavebeeninprocessforfortyyears･Butdespite

thisexperience,inDakarareas(Senegal),ithaslongbeenrecognizedthatswellingandshrinkage

Ofexpansive soils cause severe damage _overlying _{rcsidentialstructures,a触r} _experiencIng moisturechanges･Excessivewettinganddryingcausesdamageduetodi脆rentialsettJementor faiIurewithinbuildings･Theproblemofcrackingonstructuresisindeedseriousandinmanycases

COStly･Itisnotunusualforhomeownersandbuyerstosee､Ciacksinwalls.Theo句ectiveofthis

Prqjectresearchisto爪ndout?Suitable,eCOnOmicaldesignoffoundationandrecommendations

thatpreventenglneerlngStruCtureS&omseveredi能rendalsettIementsandtoimprovethebearlng CaPaCityofthe soilfoundation･Againstdisastermitigation,theconstructiorlteChniqueswith

SOiI-bagshavebeenprovedtobee爪cientforsdilbearingcqpacityimprovement,highsettlement

COntrOl,reduction oftrafnc vibrations,retaining walls and slope stability･･･SOil-bagis the COnStruCtionmethodthatconsisttopacksoilintoatextilebag･Soi)-bagsarenotcostlyatall

(COmParedtoconstructionmethodswithcementstabilization,piling…).Furthermore,aSareSultof

PreVious studies and叩Plications ofsoil-bagsinpermanent englneerlng StruCtureS,the earth reinforcing method uslng SOil-bagsis proposedin this research

_prqject

to bypass _the above-mentionedgeotechnicalproblemsinDakarareas･Adequateandexhaustivespecincationsfor

SOil-bags,designandconstructionaredetailedinthisstudy.

論文審査結果の要旨

Thecontentofthisresearchworkscanbedividedintothreeparts,eXperimentalinvestigations andanalysesonstructuredgeomaterials,mOdelingandnumericalsimulationsofthemechanical

behaviors _{ofvarlOUSJapanese} _{struCturedgeomaterials,and} _{atlast,PreSentation} _ofatechnical

PrOPOSalofconstructiononproblematicsoilinSenegal.

Thebehaviorofthesoiland/orrockatthelocationofanycivilenglneerlngStruCtureShas● ●

m往IOrinnuenceonthesuccess,eCOnOmyandsafヒtyofthework.Forthisreason,tOPrOPerlydeaI

(5)

mustbeunderstood.Since岳軌cturedgeomaterialsareinvoIvedinmanygeotechnicalproblems, muchattentionhastobepaidtothemechanicalbehaviorofnaturalsoils･Soiltesting,therefbre, playsanimportantroleincivilenglneerlng･Geomaterialin-Situusuallypossessesnaturalstructure, whichenablesthemtobehavedi馳rentlyftomthesamematerialin?reCOnStitutedstate･Theterm

`struCture,dennedqsthecombinationoffhbric(arrangementofparticles)andinterparticlebonding

isrepottedinawiderangeofliteraturetohaveeL7bctsonthemechanicalbehaviorofnatural geomaterials･Itisalsowidelyreportedthatthestructurehaseffbctsonthemechanicalbehaviorof thegeomaterials･Forexample,WhenaIoadisappliedonastructuredsoil,thestructuremay

degradeandmaylcadtodecreaseinthestrengthoFthesoils･1argesettlementofthegro血d(Kansai

lntel･nationalAirport,fbrexampJe)･

lnthisresearch,aneXtenSive]aboratoryanalysISWaSCOnductedtoinvestigatemoreabotltthe

geotechnicaIpropel･ties and mechanicalbehavior ofstructured soils･For this pL叩OSe,a diatomaceoussoilsblock-SamPledin=iruzenbaraatOkayamaprefもcture,Japan･Theexperimental

results showthat the struCtured soilexhibitstrain softening withlarge negative.dilatancy at ditTbrentconnningpressuresduringLshearingprocess･Thepeakstl･ength,reSidualstrengthand sti恥essincreasewiththeincreaseintheconnningpressure･[tisalsoobservedthatthee能ctof theconnningpressureonthegenerationofporewaterpressureissJgnincantduringshearlng process･Thepatternoftheporewaterpressuregenerationdependsontheconnningpressure･ Underlowconnningpressures,theporewaterpressuregenerationreachesapeakbeforethepeak strengthandthendecreases･Tncontrast,thegenerationofporewaterpressureundernorma11y consolidatedconditionincreasesmonotonicallyduringthestrainso鮎ningprocess･Theobserved negativedilatancyduringstrainsofteningprocesscanbemodeledbyintroducingthedestructionof thestructureduringshearlng･AIso,triaxialcompressiontestresultsofJapaneseHolocenealluvial clays,Upper-MostPleistocenemarineclays･Thkasudiatomaceoussoilsandsedimentaryso氏rocks areusedinthisstudy･Thestress-dilatancyrelationsarecarefu11yanalysed･Twostagesareobserved･ intheevolutionofthedilatancyduringshearlng･Thenrststageisadecreaseofthenegative dilatancyassociatedwithanincreaslngStreSSratio･Thesecondstageshowsasma11decreasein dilatancyandisassociatedwithstressdrop･Thepeakofthedilatancycurvenearlycorrespondsto thepeakstrengthofthematerial･Thesoi)sexhibitsimultaneouslynegativedilatancyandstrain so氏enings･Itisalsofoundthattheoverconsolidationhistoryhase脆ctsonthedilatancy･Under lowerconRningpressures,negativedilatancylSeXhibitedatahighlevel ofstressratio･As deformationprogresses,dilatancydecreasesandtendstozero･Theeffbctofoverconsolidation vanishedcompletelyasthesoilstruCturedegradesduringshearlngPrOCeSS･Whenanultimatestate ●

(6)

is achieved,the volumechange stoppedwhi16 the shear,deformation ofsoilcontinues under constantvoidratio,atyPicalcriticalstateofsoil･Importantfヒaturesofstructuredgeomaterialsare found丘omtheexperimentalinvestigations, Asuccessfu1geo-echnicaldesigngreatlydependsonhowtowellpredictthesoilbehavior･Inthis research,neWlogisticevolutionalequations,thatconsiderthee能ctsofstructuredegradationon themechanicalbehavior,areintroducedtotheextendedelasto-plasticmodelproposedbyAdachi, Okaandlねshima.Itwasconsideredthedecreaseintheinitialvolumetriccomponentofstress historytensorandtheshrinkageoftheoverconsolidationboundarysurthcerelatedtodegradation ofthestructure.ThesampleissupposedtoinitiallybeconsolidatedisotroplCallyuptoacertain

stress.Ifthespecimetlisconsolidatedtoacertainstressstate,thensuqectedtoshearstraining,

subsequentyieldingoccurs,reSultinginthecontractionoftheloadingsur丘ICe･Thecontraction continuesuntiltheyieldsurhcecoincideswiththeorlglnalCamclayyieldsurfhce･Whennatural soilisperfヒctlydestl･uCttlred,thematel･ialisinanormallyconsolidatedstate･ Byus]ngSam9parameterS,Cam-Claymodel,anOrlglnalstrain-SOReningmodelpl･OPOSedby

AdachiandOka,itsmod描edmodelswithlogisticevolutionalequationsandexponentialequations,

areusedtosimulatethestrainsoReningwithlargenegativedilatancyexhibitedduringshearlng process･Theapplicationofthosemodelsisevaluatedthroughacomparisonbetweenthesimulated andtheexperimentalresultsonthehighlystruCturedgeomaterialsmentionedabove･Itisfoundthat

thenewmodinedmodelwithlogisticevolutiona)equationsismoreappropriate`todescribethe

strainhardeningandso6eningbehaviorwithlargenegativedilatancy･

Inthe丘･ameWOrkofproblematicgeomaterials,areSearChproposalrelatedtoeconomicaland

suitableconstructiononproblematicsoilinSenegal(W由tA魚･ica)ispresentedinthisstudy･Many

WbstA丘･icanareasofhighdensitiesofpopulationarecoastalordelta･Theyarecoveredwithrecent depositsofcompressibleclays,Silts,andmuds･Investigationsonsuchsoilshavebeeninprocess

forfortyyears.Butdespitethisexperience,inDakarareas(Senegal),ithaslongbeenrecognized

thatswellingandshrinkageofexpansivesoilscauseseveredamageoverlyingresidentialstructures･

aaer experJenClng mOisture changes･Excessive wetting and drying causes damage due to

di脆rentialsettlementorfailurewithinbuildings.Theo句ectiveofthisprqjectresearchisto爪nd

outasuitable,eCOnOmicaldesignoffbundationandrecommendationsthatpreventenglneerlng

structures什om severe di飴rentialsettlements andtoimprove the bearlngCaPaCity ofthe soil foundation.Against disastermitigation,the _construction techniques with soil-bags have been provedtobeefficientforsoilbearlngCapaCityimprovement,highsettlementcontrol,reductionof

(7)

consistsf6packsoilintoatextilebag･Soil-bagsarenotcostlyatalI(COmParedtoconstruction

methodswithcementstabilization,Piling…).Adequateandexhaustivespeci丘cationsforsoil-bags,

designandconstructionaredetailedinthisstudy･

Experimental study on the mechanical behavior of highly structured geomaterials and its modeling

Title