Preliminary study on modeling thermo-hydro-mechanical coupling behavior of unsaturated soils based on hybrid mixture theory

Thermo-hydro-mechanical (THM) coupling processes in unsaturated soils are very important in both theoretical and engineering applications. A coupled formulation based on hybrid mixture theory is derived to model the THM coupling behavior of unsaturated soils. The free-energy and dissipative functions for different phases are derived from the Taylor's series expansions. Constitutive relationships of the THM coupled behavior for unsaturated soils, which include deformation, entropy change, fluid flow, heat conduction, and dynamic compatibility conditions on the interfaces are then established. The number of field equations is shown to be equal to the number of unknown variables; thus, a closed problem is formed. In addition to the modification of the physical conservation equations with coupling effect terms, the constitutive equations, which consider the coupling of elastoplastic deformation of the soil skeleton, fluid flow, and heat transfer, are derived