A critical saturated state-based constitutive model for volumetric behavior of compacted bentonite

In recent years, more and more unique volumetric behaviors, including the nonlinear compression and unloading curves in the e-lnp plane, and different types of swelling and shrinkage curves obtained from suction-controlled swelling and shrinkage tests, etc., which are significantly different from those of nonexpansive clays, have been reported on compacted bentonite. More importantly, limitations were encountered when describing the unique behavior with existing constitutive models for unsaturated expansive soils. In this study, a new concept of critical saturation state (CSS) was proposed for compacted bentonite, in which, as the saturated state was reached, the matric suction still remained nonzero in the soil. Incorporated with this concept, a constitutive model was proposed. In this model, the CSS curve was defined in the suction-isotropic stress plane, delimiting the unsaturated zone. To validate the model, the volume change tests conducted on compacted GMZ bentonite under different stress paths were simulated. Good agreement confirmed that the proposed model could well describe the volume change behavior, including the swelling on hydration, shrinkage during drying, nonlinear compression, and unloading behavior. Key words: compacted bentonite, constitutive model, critical saturated state (CSS) curve, nonlinear compression and unloading behavior, swelling and shrinkage behavior Ces dernieres annees, de plus en plus comportement volumetrique unique, y compris les courbes non lineaires de compression et de dechargement dans le plan e-lnp, differents types de courbes de gonflement et de retrait obtenues par des essais de gonflement et de retrait controles par aspiration, etc., qui sont sensiblement differents de ceux des argiles non expansives, ont ete rapportes sur la bentonite compactee. Plus important encore, des limites ont ete rencontrees lors de la description de ce comportement unique avec les modeles constitutifs existants pour les sols expansifs non satures. Dans cette etude, un nouveau concept d'etat de saturation critique (CSS) a ete propose pour la bentonite compactee. Dans lequel, lorsque l'etat de saturation est atteint, la succion matricielle reste non nulle dans le sol. Incorpore a ce concept, un modele constitutif a ete propose. Dans ce modele, la courbe CSS a ete definie dans le plan de la contrainte de succion-isotropique, delimitant la zone non saturee. Pour valider le modele, les essais de changement de volume effectues sur la bentonite GMZ compactee sous differentes trajectoires de contrainte ont ete simules. Les bons accords ont confirme que le modele propose pouvait bien decrire le comportement de changement de volume, y compris le gonflement lors de l'hydratation, le retrecissement lors du sechage, le comportement non lineaire de compression et de dechargement. [Traduit par la Redaction] Mots-cles : bentonite compactee, modele constitutif, courbe d'etat de saturation critique (CSS), compression et dechargement non lineaires de dechargement, comportement de gonflement et de retraction
Introduction Compacted bentonite has been selected as a buffer/backfill material for constructing deep geological repositories for disposal of high-level radioactive waste in many countries (Komine and Ogata 1996; Villar 2006; [...]