This chapter conducts a 3D numerical analysis of the PRACLAY in situ heating test to simulate the long-term THM response of Boom Clay. Utilizing the THMD constitutive model from Chapter 3 and the thermo-elasto-plastic creep damage model from Chap. 5, the simulation incorporates excavation-induced disturbance, self-sealing effects, and temperature-dependent hydraulic conductivity evolution. The numerical model captures the coupled THM behavior across four operational phases: initial excavation, creep initiation, 10-year heating, and subsequent cooling. Results predict the spatial and temporal evolution of temperature distribution, pore pressure gradients, creep strains, and damage zone development. The analysis demonstrates the capability of advanced THM models to interpret complex field-scale heating experiments, supporting the long-term safety assessment of high-level radioactive waste repositories in clay formations.