A multi-phase/multi-regime modelling approach for saturated granular media

When studying, by using continuum-based approaches, liquefaction phenomena, granular flows and granular material reconsolidation, crucial is the correct modelling of the change in material behaviour due to water presence and force chains collapse. To this aim, in this paper, the authors outline a model based on an in-parallel scheme. Three stress contributions are defined: the one associated with force chains applied to the solid skeleton (the effective stress), the one related to particle collisions (dominating for large values of void ratios and when the system is agitated) and the liquid one (not necessarily isotropic for large deviatoric strain rates). The model is conceived to reproduce the material mechanical behaviour of granular media under three different regimes: solid like, fluid like and inertial. The transition from one regime to another, in the model, is governed by the evolution of two state variables: void ratio and granular temperature (a measure of the material agitation). In this paper, the saturated version of the multi-regime model, already conceived for dry granular materials, is proposed. Its capability of reproducing the material fluidization in undrained constant volume rheometer tests is illustrated by discussing the numerical results obtained by using a Material Point Method code.