Structural changes in granular materials: The case of irregular polygonal particles

This paper presents a series of numerical simulations of biaxial tests performed on assemblies of two-dimensional irregular polygonal particles. Each sample is prepared with a technique similar to dry pluviation. Different aspect ratios (1–3) are considered and the behavior of granular samples is analyzed from both a global and a local point of view. More precisely, the influence of the particle aspect ratio on both inherent (initial) and induced anisotropy is investigated. New internal variables which are related to the orientation of particles are proposed. They give new insight into the specific mechanisms that control the behavior of irregular polygonal materials. Associated to global variables, they demonstrate the existence of a critical state irrespective of the investigated aspect ratios. However, for materials with higher aspect ratios (2 and 3), their inherent anisotropy prevents any extensive reorganization, this means that, within the range of usual strains considered in civil engineering, the particle reorientation remains in progress and considerable deformations are required to reach the critical state.