A theory of plasticity with generalized hardening for natural geomaterials under mechanical and environmental loading: Constitutive modeling and numerical implementation

An extended theory of plasticity with generalized hardening is proposed to describe the response of geomaterials under both mechanical and environmental processes. It is assumed that the coupling between mechanical and environmental processes takes place at two levels: A) as an additional direct contribution to the constitutive stress changes, taking place even for purely elastic processes; and, b) as a consequence of the evolution of the internal state variables of the material with the changes in the environmental process variables. This last effect is incorporated through a set of generalized hardening rules. The general formulation is then specialized to the case of calcarenite rocks under unsaturated conditions, which can experience significant degradation processes due to plastic deformations, changes in degree of saturation (short-term debonding) and chemical dissolution of the bond material and the solid grains (long-term debonding). The resulting model, implemented in a FE code through the GBE algorithm extended to incorporate the full formalism of plasticity with generalized hardening, demonstrate the practical relevance of environmental degradation effects in practical applications, over periods of time comparable with the life cycle of most geotechnical structures.