Deep geological repository involving a multi-barrier system constitutes one of the most promising options for isolating high-level radioactive waste from the human environment. In order to certify the efficiency of waste isolation it is essential to understand the behaviour of confining geomaterial under a variety of environmental conditions. To this end, results from a near-to-real scale experiment, the FEBEX in-situ experiment, are studied by means of a thermo-hydro-mechanical (THM) finite element approach, including a consistent thermo-plastic constitutive model for unsaturated soils. Laboratory tests are simulated to calibrate model parameters. The results of the numerical simulations are compared with sensor measurements and show the ability of the model to reproduce the main behavioural features of the system. The influence of the hysteretic and temperature-dependent retention of water on the mechanical response is exhibited. Finally, those results are interpreted in the light of thermo-plasticity of unsaturated soils, which reveals the highly coupled and non-linear characters of the processes encountered.