SUMMARYWe investigate a polydisperse granular material in which the particle interactions are governed by a capillary force law. The cohesion force for a grain-pair with unequal diameters is expressed as an explicit function of the inter-particle distance and the volume of the liquid bridge. This analytical relation is validated by experiments on a reference material. Then, it is completed by a rupture criterion and cast in the form of a force law that accounts for solid contact, capillary force and rupture characteristics of a grain-pair. Finally, in order to evaluate the influence of capillary cohesion on the macroscopic behaviour, radial and axial compression tests on cylindrical assemblies of wet particles are simulated using a 3D distinct element method.

Definition and experimental determination of a soil-water retention surface S. Salager, M.S. El Youssoufi, and C. SaixAbstract: This paper deals with the definition and determination methods of the soil-water retention surface (SWRS), which is the tool used to present the hydromechanical behaviour of soils to highlight both the effect of suction on the change in water and total volumes and the effect of deformation with respect to the water retention capability. An experimental method is introduced to determine the SWRS and applied to a clayey silty sand. The determination of this surface is based on the measurement of void ratio, suction, and water content along the main drying paths. These paths are established for five different initial states. The experimental results allow us to define the parametric equations of the main drying paths, expressing both water content and void ratio as functions of suction and initial void ratio. A model of the SWRS for clayey silty sand is established in the space (void ratio -suction -water content). This surface covers all possible states of the soil inside the investigated range for the three variables. Finally, the SWRS is used to study the relations between water content and suction at a constant void ratio and between void ratio and suction at a constant water content.Key words: water retention, hydromechanical coupling, retention behaviour.Résumé : Cet article traite de la définition et des méthodes de détermination de la surface de rétention sol-eau (« SWRS ») comme outil de représentation du comportement hydromécanique de sols permettant de mettre en évidence à la fois l'effet de la succion sur les changements de volumes (volume d'eau et volume total) et l'effet de la déformation sur la capacité de rétention d'eau des sols. Une méthode expérimentale de détermination de la SWRS du sol est présentée en détails puis appliquée pour un sable limoneux argileux. La prise en compte de la déformation conduit à une représentation surfacique à partir de la mesure de triplets (indice des vides -succion -teneur en eau) le long des chemins de séchage principaux. Ces chemins sont établis pour cinq états initiaux différents. Les résultats expérimentaux permettent d'établir les équations paramétriques des chemins de séchage principaux exprimant l'indice des vides et la teneur en eau en fonction de la succion et de l'indice des vides initial. Un modèle de surface caractéristique sol-eau est élaboré pour le sable limoneux argileux dans l'espace (indice des vides -succion -teneur en eau). Cette surface couvre tous les états possibles du sol dan les gammes étudiées des trois variables. La SWRS est finalement utilisée pour Õ tudier les relations entre la teneur en eau et la succion pour un indice des vides constant, et entre l'indice des vides et la succion pour une teneur en eau constante.

We investigate the macroscopic mechanical behaviour of wet polydisperse granular media. Capillary bonding between two grains of unequal diameters is described by a realistic force law implemented in a molecular-dynamics algorithm together with a protocol for the distribution of water in the bulk. Axial-compression tests are simulated for granular samples at different levels of water content, and compared to experiments performed in similar conditions. We find good agreement between numerical and experimental data in terms of the rupture strength as a function of water content. Our results show the importance of the distribution of water for the mechanical behaviour.

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This paper presents a unified thermo-mechanical experimental study on a remoulded unsaturated sandy silt and brings a contribution to the understanding of the fundamental mechanics of unsaturated soils in non-isothermal conditions. The experimental program was carried out at four temperatures and four suction levels using two thermo-hydro-mechanical (THM) cells, one isotropic and the other oedometric. The effect of suction and temperature on the compressibility and on the apparent preconsolidation pressure of the soil is addressed. Finally, an analytical expression of the evolution of the apparent preconsolidation pressure with respect to temperature and suction is proposed.

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International audienceIn this paper, a theoretical and experimental investigation of the effect of temperature on water retention phenomena in deformable soils is presented. A general law expressing the change in suction with water content, temperature and void ratio is proposed theoretically. This law accounts for the influence of density and temperature on water retention. It also provides a general framework which appears to be well-adapted to describe many particular cases. The effect of temperature is studied through a predictive relationship which is established in this framework. This relationship allows us to obtain the water retention curve at any temperature from that at a reference temperature, thus reducing strongly the number of tests required to characterize the thermo-hydraulic behaviour of a soil. The relevance of this relationship was experimentally verified from new tests as well as the results previously reported in the literature. The new tests were performed on two model media, namely, a terracotta ceramic and a clayey-silty sand. The tests taken from the literature concerned two different clays. Comparison between theoretical prediction and experimental data was particularly promising and shows the capability of the model to cover a wide range of soils

vides. Connaissant la courbe de rétention à une température donnée, le modèle permet de la prédire pour d'autres températures. Des résultats d'essais expérimentaux, réalisés à 20 et 60 • C, sur une céramique (terre cuite) et un sable limoneux-argileux, permettent de valider le modèle. L'application du modèle à d'autres résultats de la littérature montre sa capacité à couvrir une large gamme de matériaux poreux. Influence of temperature on the water retention curve of porous media. This paper concerns the influence of temperature on the water retention curve of porous media. We present a model based on the differential of suction as a function of temperature, water content and void ratio. When adjusted for a given temperature, this model is able to predict the curve for any temperature. The model was validated by several tests on a ceramic (terra cotta) and a clayey silty sand at 20 and 60 • C. The application of the model to data found in the literature confirms its predictive power for a wide range of porous materials.