Assessing the quasi-static conditions for shearing in granular media within the critical state soil mechanics framework

Abstract

There has been a marked increase in the use of the discrete element method (DEM) in geomechanics in recent years. The way in which DEM simulations are set up can have a noticeable influence on the observed response. Here the conditions for quasi-static shearing in DEM simulations of granular materials were studied within the critical-state framework of soil behaviour. Thirty two constant-p' triaxial simulations were carried out from which critical-state relationships were defined in the void ratio-mean effective stress and deviator fabric-mechanical coordination number planes. Clear trends were observed in the void ratio, coordination number and deviatoric fabric at the critical state as the inertial number, I, was varied. The critical state relationships are aligned along distinct loci for each value of I. The critical state framework is used to show that there is an upper bound to the I values below which the simulation is quasi-static and the observed behaviour is independent of strain rate. The parameter I is shown to be a useful measure to assess the quality of quasi-static DEM simulations.