[en] In a repository for high-level radioactive waste (HLW), complex thermal, hydraulic and mechanical (T-H-M) phenomena will take place, involving the radiogenic heating from the vitrified waste, infiltration of ground water and swelling pressure in the buffer. It is one of the important subjects to evaluate these phenomena for the geological disposal of HLW, therefore an in-situ T-H-M experiment was conducted. A test pit was excavated in the floor of the test drift and the buffer material and a heater were set up in the test pit, and then coupled T-H-M test was started. The change of temperature, water content, total pressure and strain were measured both in the buffer and the rock mass. The phenomena in the unsaturated buffer were evaluated by a fully coupled T-H-M model. Comparison between measurements and predictions showed good agreement about the temperature and water content. However, it needs more study to evaluate the mechanical phenomena in the unsaturated swelling material such as the bentonite clay. (author)