A unified thermoplastic/viscoplastic constitutive model for geomaterials

Research on the effect of temperature changes on the behaviour of geomaterials has become increasingly important in recent years. This growing interest is partially due to the recent development of high-level nuclear waste disposals. Because of the complex influence of temperature in these areas, it is necessary to understand the effects of temperature on rock-like materials and use the appropriate constitutive equations to numerically model these phenomena. In this paper, a thermoplastic/viscoplastic constitutive model is developed for this purpose. The model includes thermal softening, the evolution of the yield functions with temperature, and the effects of temperature on the time-dependent behaviour. The model performance is demonstrated by some simple test cases on Tournemire and Bure clayey rocks including triaxial compression tests and creep tests under constant temperatures. The numerical results are discussed using experimental data, which demonstrate that the model can reproduce the overall behaviour of this type of materials under deviatoric loads and non-isothermal conditions.