A modified oedometer apparatus for experimentally obtaining the soil-water retention curve

M. Nuth

Dans les comptes rendus d’articles de la conférence: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: FUNDAMENTALS - IX Physical & Numerical Modelling

ABSTRACT: AModifiedsetup forautomaticoedometer apparatus wasdesignedat Universit• de Sherbrooke. The proposed setup canbe used tosimultaneouslymeasure the volume change and water retention capability of unsaturated soilscoupled withaxistranslation ornegative water column techniquesto control suctionalong withhavingconventional features ofoedometer apparatus.This paperdescribesthemodifications made to improve theautomatedoedometer apparatusinaddition tothe details ofcalibration and test procedure.Somepreliminarysoil-water retention curves(SWRCs)on granularmaterialsobtainedwith the unsaturated oedometerapparatusarepresented here.Moreover,based on SWRC modelsand fitting process usingindex properties proposed byvarious authorstheSWRCcorresponding to granular materialsused in this paperwas regeneratedandcompared with the obtained experimental data.R†SUM†Unecellule oedom•triqueautomatiquemodifi•e a •t• con‡ue … l—Universit• de Sherbrooke. Lemontage propos• offre lapossibilit• de mesurer simultan•ment les changements de volume et les propri•t•s de r•tention d—eau des sols non-satur•s, en combinant la translation d—axe ou la colonne d—eau n•gative pour contr–ler la succion avec les chargementsoedom•triques conventionnels. Cet article d•crit les modifications apport•es … l—appareil de consolidation oedom•triqueautomatique et discute de sa calibration et du protocole d—essai. Plusieurs courbes de r•tention d—eau pr•liminaires ont •t•obtenues pour des sols granulaires … l—aide du dispositif pr•sent•. De plus, les courbes de r•tention d—eau ont •t• pr•dites… l—aide de plusieurs modƒles de la litt•rature bas•s sur la granulom•trie des sols test•s et sont compar•es aux r•sultatsexp•rimentaux.1INTRODUCTIONFrom experimental and theoretical viewpoints, distinctassessment of soilbehavior in partially saturated conditionhas become evident since the keyconceptsof classic soilmechanics are not necessarilysufficientfor partiallysaturated media(Aitchison, 1960; Aitchison & Donald,1956; Bishop & Blight, 1963; Fredlund, Rahardjo, &Fredlund, 2012; Jennings & Burland, 1962).In the pastdecades, significant breakthroughswere achievedinjustifying and modelling the partially saturated soilbehavior. However,having access to acceptableexperimental datahas an important rolewhich can beconsidered as one of the main limitations on validation ofavailable models.Due tothenature of partially saturated soils, theconventional methods to perform laboratory tests are notsatisfactory and routinelaboratoryapparatusesshouldbecorrespondingly modified.Based on the difficulties faced inperformingtests on partially saturated soils, variousmodified triaxial, oedometer and shear box apparatuseshave been proposed anddesigned to use recently(Ng etal.(2010); Jotisankasa et al(2006);Fran‡ois & Laloui,(2010)).This paper reports on amodifiedautomatic oedometersetupthat hasbeenassembled at Universit• deSherbrookewhich has the ability to not only beusedasconventional oedometer device but also to be employed forsimultaneously measure volume change during suction-controlled testsbyperforming axis translation ornegativewater column techniques.ThebaseframeofAutomaticOedometer System (AOS), air and water controllers aremanufactured by GDSinstrument Ltd.This paper presentssome experimental tests that are partsof alargerprojecttargeted to examine the effectivestress approach forgranular materials. Thetargetproject is divided into threeparts;I)obtaining experimental data of soil volume changein elastic range II) performing the shear strength tests infailure and non-failure conditions, and III) modelling theresults using discrete element methods (DEM). The paperhighlights the difficulties inperformance of theunsaturatedtests, the achieved SWRCs and comparison ofexperimentaldata with estimated results ofSWRC modelsbased onphysicalproperties of materials2CONTROLLING OF SUCTION LEVELSuction in soils causes the stress regime to change whichresults in varying the strength and volume change ofpartially saturated soils.Consequently, measuring andcontrollingthe suction in laboratory and in-situ isnecessary.There are numbers of teststhat can beimplemented in field to measure suction,however,controlling suction in field in large scale isnot yet practicallypossible and as a result, suctioncontrolledtests areessentiallycarried out at thelaboratoryscale. The suctionmeasurement and control methods are divided into twomajor categories. Infirst category,the direct methods,onlymatricsuction is evaluated and the equilibrium of water andsoil is studied without the aid of anyexternalagent mostlyusing tensiometers,axis translationand negative watercolumn techniques. In secondcategory,the suction is

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