Boom and Ypresian clays are being studied in Belgium in connection with the design of a repository for radioactive waste. Within this context, thermal impact may play an important role on the behaviour of these low-permeability clays. To evaluate this impact, heating pulse tests on intact borehole samples were carried out using an axi-symmetric and constant volume heating cell with controlled hydraulic boundary conditions. Attention is focused on the time evolution of temperature and pore water pressure changes along heating and cooling paths -i.e., pore pressure build-up during quasi-undrained heating and later dissipation to the applied hydraulic boundary conditions. A coupled thermo-hydro-mechanical finite element program was used in a first stage to determine thermal parameters by back-analysis and then to simulate selected experimental results on Boom clay