Effect of short- and long-term nonlinear behaviour on the thermoporomechanical pressurisation in COx claystone
Résumé
This study focuses on assessing the effect of short- and long-term nonlinear deformation (plasticity and creep) on the thermo-hydro-mechanical (THM) responses of Callovo-Oxfordian (COx) claystone, considered as the host formation for the geological radioactive waste disposal in France, if it is licensed. The temperature increase due to heat emitted from the waste package induces a pore pressure rise in low permeability porous rocks such as the COx claystone, due to the difference in the thermal expansion coefficients between water and the argillaceous skeleton. This phenomenon has been evidenced by laboratory and in situ heating experiments. Recently, the key THM phenomena taking place around the high-level radioactive waste (HLW) repository based on the French concept, have been investigated using a thermoporoelasticity approach. In this paper, certain nonlinearities observed in the mechanical behaviour of the COx claystone have been considered in the evaluation of these THM processes. Three numerical simulations (thermoporoelastic, thermoporoelastoplastic and thermoporoelastoviscoplastic) are performed using Comsol Multiphysics code, in which the time-dependent behaviour of the COx is described by a power law whereas the elastoplastic behaviour is modelled by a strain hardening with a Hoek-Brown criterion and a non-associative flow rule. The role of elastoplastic and viscoplastic parts of deformations on the temperature, pore pressure and stresses time evolution in the far-field, is highlighted.