Modelling of volume change in granular materials in relation to their internal state

Numerical simulations on samples composed of rigid spheres have been performed to study the behaviour of granular materials under complex stress paths involving peculiar triaxial monotonous stress paths and two-way cycling loading paths. These simulations using the Discrete Element Method (DEM), pointed out the concomitant role played by the void ratio and the anisotropy of fabric in the behaviour of these samples. Thus, the void ratio and the anisotropy of fabric have been chosen as internal variables for the description of the internal state of the material. An elastic-plastic model for soils, CJS, has been used to study the evolution of the material at the global scale. This work shows the complex path followed by some variables or key parameters involved in this model throughout simulations. Moreover, the parameters that are usually taken as constants in the CJS model definitely need to evolve with respect to the two internal variables in order to provide a precise prediction of the behaviour of granular materials throughout complex loadings. (C) 2010 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.