Search

A new unsaturated soil model was recently developed at Ecole Nationale des Travaux Publics de l'Etat (ENTPE), based on the concept of bounding surface plasticity. The first version of this model (by Morvan et al. in 2010) only required 12 parameters for its definition, and yet can simulate a few behaviors typically observed on unsaturated fine sands, which more classical models fail to reproduce. These include post-peak softening, change from contractant to dilatant behavior during shearing, and the smooth transition from elastic to elastoplastic behavior upon yielding. Subsequent to this first publication, additional mechanisms have been introduced in the model previously developed. Among them, the hysteretic phenomenon during cyclic variations of suction and water content, as well as the effects of porosity change on water retention characteristics, are now taken into consideration. To this end, the water content is introduced as an independent generalized strain variable, which is no longer uniquely linked to suction. Thanks to these developments, the model can now account for the bilateral couplings between hydraulic and mechanical quantities, with good precision under very general loading conditions. In the present paper, these new developments are presented in detail, and the experimental basis of this construction is discussed. The model is then validated using existing experimental data on kaolin, by considering two stress paths. The first stress path consists of a single cycle of wetting followed by drying at constant isotropic stress. The second, more complex loading path involves simultaneous variations of suction and isotropic compression or decompression. The results confirm overall the satisfactory performance of the model. The main conclusions are then summarized in the last section, including perspectives for future developments. Key words: bounding surface plasticity, suction hardening, critical state line, limit state line, experimental validation, hydraulic hysteresis, hydromechanical coupling. Un nouveau modele de sol non sature a ete developpe recemment a Ecole Nationale des Travaux Publics de l'Etat (l'ENTPE), selon le concept de la surface limite de plasticite. La premiere version de ce modele (par Morvan et al. en 2010) necessitait seulement 12 parametres pour sa definition, mais pouvait tout de meme simuler quelques comportements typiques observes sur des sables non satures dont les modeles plus classiques n'arrivaient pas a reproduire. Ceux-ci incluent l'adoucissement post-pic, le changement d'un comportement contractant a un comportement dilatant durant le cisaillement, et la transition graduelle d'un comportement elastique a elasto-plastique a la limite elastique. Suite a cette premiere publication, des mecanismes additionnels ont ete introduits au modele developpe precedemment. Parmi ces mecanismes, le phenomene d' hysteresis durant les variations cycliques de la succion et de la teneur en eau, et les effets de la variation de la porosite sur les caracteristiques de retention d'eau, sont maintenant consideres. Ainsi, la teneur en eau est introduite en tant que variable independante generalisee de la deformation qui n'est plus seulement liee a la succion. Grace a ces developpements, le modele peut maintenant considerer les couplages bilateraux entre les quantites hydrauliques et mecaniques avec une bonne precision sous des conditions de chargement tres generales. Dans cet article, ces nouveaux developpements sont presentes en details, et la base experimentale de l'elaboration est discutee. Le modele est ensuite valide a l'aide de donnees experimentales sur le kaolin en considerant deux cheminements des contraintes. Le premier cheminement des contraintes consiste en un seul cycle de mouillage suivi par le sechage a une contrainte isotrope constante. Le deuxieme et plus complexe cheminement des contraintes implique des variations simultanees de la succion et de la compression ou decompression isotrope. Les resultats confirment la performance globalement satisfaisante du modele. Les principales conclusions sont ensuite resumees dans la derniere section, incluant des perspectives pour le developpement futur. Mots-cles : surface limite de plasticite, durcissement par succion, ligne de l'etat critique, ligne de l'etat limite, validation experimentale, hysteresis hydraulique, couplage hydromecanique. [Traduit par la Redaction], Introduction During the last 20 years, a certain number of theoretical models were built to simulate the behavior of unsaturated soils. The Barcelona basic model (BBM) developed by Alonso et [...]