Simulating pressure-induced compaction by grain rearrangement

This article presents a novel model of the compaction of loose sand, or other granular material, incorporating two dilatancy terms. One is negative, reflecting the general tendency of an assembly to collapse under a combination of shear stress and pressure. The other develops during shear straining and, at the critical state, is sufficiently large and positive to counter the negative contribution. The existence of a term producing negative dilatancy, however, suggests the concept of ‘self-cancelling shear deformation’. These shears contribute to the shear–volume coupling, producing densification, but not to the macroscopic shear deformation. They only occur when there is a small amount of damage. This produces pressure-induced densification by granule rearrangement, resulting in a model where compaction is possible under a hydrostatic load but the model can still simulate cyclic deformation and critical state behaviour.