THMC constitutive model for membrane geomaterials based on Mixture Coupling Theory

Modelling of coupled thermal (T), hydro (H), mechanical (M) and chemical (C) processes in geomaterials has attracted attention in the past decades due to many significant contemporary engineering applications such as nuclear waste disposal, carbon capture and storage etc. However, in very-low permeability membrane geomaterials, the couplings between chemical osmosis and thermal osmosis and their consequent influence on temperature, water transport and mechanical deformation remain as a long-lasting challenge due to the gap between geomechanics and geochemistry. This paper extends Mixture Coupling Theory by bridging the chemical-thermal field based on non-equilibrium thermodynamics, and develops a new constitutive THMC fully-coupled model incorporating the interactions between chemical and thermal osmosis. Classic Darcy's law has been fundamentally extended with osmosis as the major driving force of the diffusion process. A simple numerical simulation used for the demonstration purpose has illustrated that the couplings between chemical and thermal osmosis will significantly change the water flow directions, consequently influencing the saturation variation and mechanical deformation.