Micromechanics of dilatancy and critical state in granular matter

Abstract

To understand the microscale mechanisms that govern dilatancy and critical state, the changes in topology of a granular assembly during numerical simulations of quasi-static deformation are analysed. In this article we show that explanations for these unique features of granular matter lie in the interplay of evolving frequency of microscopic topological events (flips) and elastic relaxation of particles, both of which are consequences of the history-dependent organisation of interparticle forces in force chains. Specifically, dilatancy has two components – one is the result of increasing frequency of flips and the other arises from the elementary volume increases that accompany the flips as elastic relaxation. The critical state arises as the balance between the dilation rate and the compaction rate under shear-induced disturbances.