State Concept and Modified Elastoplasticity for Sand Modelling

Abstract

An elastoplastic deformation law for sands incorporating the state concept is formulated. These fundamental concepts for modelling and characterization of sand behaviour are unified in order to build a rational sand model that enables integral modelling over a wide range of density and normal stress states. A modified hyperbolic stress-strain relation and an energy based stress-dilatancy relation are used as basic relations that embody the essence of sand behaviour into the constitutive model. The stress-strain relation is established within the framework of the state concept and uses the state index Is to quantify the effects of the relative initial state (initial density and normal stress state) on the stress-strain curve. These effects are reflected on the dilatancy of the sand by specifying that the principal parameter of the stress-dilatancy relation depends on the shear strain. The most distinctive features of the plasticity formulation are the assumptions for continuous yielding and the dependence of the plastic strain increment direction on the stress increment direction. The ability to model undrained sand behaviour for various relative densities with the same values of the material parameters is demonstrated.