Micromechanical approach of capillarity in granular media : water retention and mechanical behaviour
This work deals with study of humid granular media. We mainly study media containing weak water percent (around 2%). The influence of capillarity on water retention and mechanical beha- viour is analyzed. At each state of equilibrium, water distribution is obtained by applying a homogeneous suction in the entire elementary representative volume. The approach is a multi-scale approach based on experimental/modelling at the local scale (interaction between grains) and produces discrete element simulations of the macroscopic behaviour which are compared to experimental results. At the scale of interactions, an experimental study of the liquid bridge piloted by suction validates a model based on the toroidal approximation of the liquid bridge shape. At constant suction, we note that the criterion of rupture proposed by Lian in the case of traction at constant volume is no more valid. At the macroscopic scale, simulated water retention curves are close to experimental water retention curves made on a model sample composed of glass beads. Then, the mechanical behaviour is simulated. We remark a loss of co- hesion in function of suction because of the reduction of the liquid bridge density. The introduction of a roughness allows a best representation of the transition between the non saturation state and the dry state. The analysis of the stress reveals the pertinence of the stress tensor associated with traction interactions to analyze the evolution of rupture stress (simple compression) in function of suction.