Yield loci for an anisotropic granular assembly.

Yield loci of a granular material are derived in case of triaxial compression carried out at constant pressure. The theory is based upon a simple micromechanical model in which particles move according to an average, homogeneous deformation. We show how the presence of an inherent anisotropy in the aggregate (typical of laboratory samples due to depositional processes) produces a deviation of the yield loci in the stress space from the expected Mohr-Coulomb prediction. That is, when the compaction pressure in an anisotropic aggregate is increased, irreversibility associated with sliding between particles occurs and this will influence the yield function in the subsequent triaxial test. Numerical simulations support the theoretical result.