The paper presents a study of the undrained behaviourof an uncemented carbonate sand (Quiou sand) undersimple shear loading conditions. The experimental studywas conducted through cyclic and monotonic undrained/constant volume simple shear tests carried out on reconstitutedspecimens prepared by using the sedimentationin water (WS) method. Tests were carried out on specimensreconstituted at two void ratios (i.e. loose anddense) and different effective consolidation stresses.Furthermore, to account for the effect of non-zero meanshear stress level, cyclic simple shear tests were performedunder both symmetrical and non-symmetricalcyclic loading. Two types of failure modes have beenobserved in cyclic tests, that is ‘cyclic liquefaction’ or‘cyclic mobility’, depending on whether or not they wereconducted under shear stress reversal conditions. A unifiedframework seems to exist whereby undrained monotonicand cyclic response can be comparatively analysed.In particular, normalising the cyclic liquefaction resistancesobtained from symmetrical tests by phase transformationstrengths determined in corresponding monotonictests, provides a cyclic liquefaction resistance curve whichwas found to be unique, irrespective of initial void ratioand vertical effective stress. Undrained cyclic shearstrength of the tested sand appears to be affected by thepresence of a non-zero mean shear stress, following apattern of behaviour, which is similar for both loose anddense specimens. Furthermore, the normalised stress–strain curves of the cyclic tests show back-bone curvesthat are practically coincident with the equivalent monotoniccurves.

Undrained monotonic and cyclic simple shear behaviour of carbonate sand

PORCINO D
;
2008

Abstract

The paper presents a study of the undrained behaviourof an uncemented carbonate sand (Quiou sand) undersimple shear loading conditions. The experimental studywas conducted through cyclic and monotonic undrained/constant volume simple shear tests carried out on reconstitutedspecimens prepared by using the sedimentationin water (WS) method. Tests were carried out on specimensreconstituted at two void ratios (i.e. loose anddense) and different effective consolidation stresses.Furthermore, to account for the effect of non-zero meanshear stress level, cyclic simple shear tests were performedunder both symmetrical and non-symmetricalcyclic loading. Two types of failure modes have beenobserved in cyclic tests, that is ‘cyclic liquefaction’ or‘cyclic mobility’, depending on whether or not they wereconducted under shear stress reversal conditions. A unifiedframework seems to exist whereby undrained monotonicand cyclic response can be comparatively analysed.In particular, normalising the cyclic liquefaction resistancesobtained from symmetrical tests by phase transformationstrengths determined in corresponding monotonictests, provides a cyclic liquefaction resistance curve whichwas found to be unique, irrespective of initial void ratioand vertical effective stress. Undrained cyclic shearstrength of the tested sand appears to be affected by thepresence of a non-zero mean shear stress, following apattern of behaviour, which is similar for both loose anddense specimens. Furthermore, the normalised stress–strain curves of the cyclic tests show back-bone curvesthat are practically coincident with the equivalent monotoniccurves.
La pre´sente communication donne des informations surle comportement non draine´ d’un sable carbonate´ noncimente´ (Quiou) soumis a` de charges de cisaillementsimple. L’e´tude expe´rimentale a e´te´ mene´e par le biasisde tests de cisaillement simples cycliques et monotonesnon draine´s/a` volume constant, effectue´s sur des spe´cimensreconstitue´s pre´pare´s en utilisant la me´thode dese´dimentation dans l’eau. Des tests ont e´te´ effectue´s surdes echantillons reconstitue´s avec deux indices de vide (a`savoir laˆche et dense), et diffe´rentes contraintes de consolidation.En outre, dans le but de tenir compte del’effet d’un niveau de contrainte de cisaillement moyennenon nul, des tests de cisaillement simples cycliques onte´te´ effectue´s sous charge cyclique syme´trique et asyme´trique.On a releve´ deux types de modes de de´faillance aucours des tests cycliques, a` savoir « lique´faction cyclique »et « mobilite´ cyclique », selon que ces tests e´taient effectue´s, ou non, en condition d’inversion des contraintes decisaillement. Il semble que l’on soit en pre´sence d’uncadre unifie´ dans lequel il est possible d’effectuer uneanalyse compare´e des re´ponses monotones et cycliquesnon draine´es. En particulier, la normalisation des re´sistancesde lique´faction cyclique, obtenues dans le cadre detests syme´triques, par des resistances de transformationde phase de´termine´es dans des tests monotones correspondants,permet d’obtenir une courbe de re´sistance a`la lique´faction cyclique qui s’est ave´re´e unique, inde´pendammentde l’indice de vide initial et des contraintesefficaces verticales. La re´sistance cyclique au cisaillementnon draine´e des sables teste´s semble eˆtre affecte´e par lapre´sence d’une contrainte de cisaillement moyenne nonnulle, suivant un tendance de comportement similairepour des spe´cimens laˆches et denses. En outre, lescourbes de contrainte - de´formation normalise´es des testscycliques indiquent des courbes de base coı¨ncidant pratiquementavec les courbes monotones e´quivalentes.
carbonate sands, earthquakes, Failure, Laboratory tests
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12318/169
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