Elastoplastic modelling of diffuse instability response of geomaterials

Abstract In this paper, we study material instabilities in geomaterials through an elastoplastic constitutive model endowed with appropriate attributes, such as stress, density and fabric dependencies. The analyses reveal the possibility of having diffuse instability, bifurcation and loss of uniqueness within the plastic limit surface. The resulting domain of bifurcation encompasses the intrinsic effects of stress–strain history, direction of loading, type of loading and fabric. The computations start at a material point level and are later on extended to an initial boundary value setting where diffuse failure of a three‐dimensional sand specimen with a random distribution of void ratio is examined. We restrict our simulations to the study of a q ‐constant laboratory experimental test under different sets of control parameters. Diffuse failure is also revealed in a slope analysis under water infiltration following similar loading paths as in the q ‐constant test. The analysis shows common material instability features observed in the above test. Copyright © 2010 John Wiley & Sons, Ltd.