Based on the experimental findings in Chap. 2 , this chapter develops a transversely isotropic thermo-hydro-mechanical-damage (THMD) model to capture the coupled behavior of Boom Clay. The proposed model incorporates elastic, plastic, and thermal damage evolution, a plastic hardening law, and hydraulic conductivity evolution within the Drucker–Prager Cap framework. It is implemented in ABAQUS via a user subroutine and calibrated using experimental data. Comparisons with test results confirm the model’s ability to predict key THM-coupled responses, including stress–strain stages and pore pressure evolution under temperature effects.