Failure criteria and flow rules of geomaterials

Abstract

ABSTRACT Essentially because of the non-associative character of geomaterials plastic strains, many bifurcations leading to various failure mechanisms exist strictly inside the plastic limit condition. The equations of the boundaries of the failure domain and of the cones of unstable stress directions are first exhibited for axisymmetric conditions. Because these bifurcation criteria can be satisfied before the localization condition, the failure mechanism is often of diffuse type. The considered constitutive relations, which are incrementally piece-wise linear or thoroughly non-linear, do not introduce any flow rule. However in a third section it is shown that a flow rule can be exhibited for the octo-linear model in axisymmetry while it disappears for more general 3D conditions. This last result is in agreement with some conclusions issued from discrete element modelling.