Numerical investigation of THM behavior in anisotropic poroelastic media: from element test to geological disposal applications

This study investigates the coupled Thermo-Hydro-Mechanical (THM) behaviour in anisotropic poroelastic media. The elastic stiffness is represented by using a cross-anisotropic constitutive model, while the water flow and the heat conduction are represented by using generalized Darcy's law and Fourier's law, respectively. Specifically, the THM formulations are modified to account for an anisotropic porous medium using anisotropic Biot's effective stress. As a verification step, numerical predictions of pore pressure evolutions subjected to mechanical and thermal loadings agree well with those obtained from analytical solutions. Numerical studies are conducted to identify the overpressure mechanism resulting from stress redistribution and thermal pressurization. As the discrepancy between Biot's coefficients and one increases, the inconsistency in the resulting pore pressures becomes more evident when using different definitions of solid pressure expression. Furthermore, a significant difference has been observed in pore pressure evolution computed by anisotropic and the equivalent isotropic Biot’s coefficient for Opalinus clay, but no obvious difference for Callovo-Oxfordian. These findings have implications for the understanding of the THM behaviour of argillaceous rocks, which benefit the potential geological applications in nuclear waste disposals.