A Thermo-Hydro-Mechanical (THM) model for partially saturated rocks is developed and implemented. The hypothesis of constant air pressure simplifies the equations and improves efficiency of calculation while still allowing the description of vapor flow. The implementation uses a fully coupled approach. Comparison against experimental data is performed. Results are promising, yet additional comparisons are required to fully validate the model and its implementation.
The necessity of THM modeling appeared in the nineties within the framework of nuclear wastes storage in deep geological formations. Models have then been extended to include the effects of temperature on the mechanical and the hydraulic behavior of rocks (Rutqvist et al. 2001, Collin et al. 2002). Accurate description but also the implementation of such coupled phenomena still remains a challenge. After defining a THM model for partially saturated rocks, its implementation is described then compared to experimental results..
In this section the governing equations of fully coupled thermo-hydro-mechanical analysis are briefly described. This is an extension to the previous work in which fully coupled hydro-mechanical analysis has been implemented (Galavi et al. 2011, Galavi 2011). Here, non-isothermal unsaturated groundwater flow, heat transport and deformation are considered. Similar to the previous work, we assume a constant gas pressure. Therefore, only one independent unknown in the fluid mass balance equation is needed which is pore water pressure. This study is based on the assumption of local thermodynamic equilibrium which means that all phases have the same temperature, i.e. only one equation of total energy is required. Consequently, the four primary variables are displacements (v), pore water pressure (pw) and temperature (T).