In a few years, safe and definitive solutions should be ready to manage large quantities of high-level radioactive waste. Deep geological repository involving a multibarrier system constitutes one of the most promising options to isolate such waste from the human environment. In order to provide reasonable assurance of the waste isolation efficiency, it is essential to understand the behaviour of the confining geomaterials under a variety of environmental conditions. In particular, variations in temperature and humidity are two main critical aspects in the short and medium term (i.e. several thousands of years). To this end, results from a near-to-real scale experiment were studied by means of a thermohydro- mechanical (THM) finite element approach including a consistent thermo-plastic constitutive model for unsaturated soils. This enabled a comprehensive understanding of the behaviour of the buffer material (bentonite).