The mechanical behavior of soils has been largely investigated using constitutive models. These are empirical relations based on laboratory tests of soil specimens. The investigation of soils at the grain scale using discrete element models has become possible in recent years. These models have provided valuable understanding of many micromechanical aspects of soil deformation. The aim of this work is to draw together these two approaches in the investigation of the plastic deformation of soils. A simple discrete element model has been used to evaluate the effect of anisotropy, force chains, and sliding contacts on different aspects of soil plasticity: dilatancy, failure, shear bands, ratcheting, etc. The discussion of these aspects raises two important questions: Is the incrementally nonlinear theory appropriate to describe the mechanical response of soils? And, does a purely elastic regime exist in the deformation of granular materials?
