Measurement of thermally-induced pore-water pressure increase and gas migration in the Opalinus Clay at Mont Terri

In order to gain a better understanding of coupled thermo-hydro-mechanical (THM) processes in indurated clays as host rock for the disposal of high-level radioactive waste, a heating experiment named HE-D is being conducted in the Opalinus Clay at the Mont Terri Rock Laboratory in Switzerland. An electric heater equipment of 5.4 m length was installed in a horizontal borehole of 30 cm diameter and 14 m length. The surrounding rock has been heated from the temperature of 15–43 °C at the heater/rock interface over the first 3 months and to 100 °C over further 8 months, respectively. The second heating phase is going for a total period of 12 months until June 2005. Following that, a cooling phase will be carried out by shutting-down the power supply for 6 months. Finally, the dismantling is scheduled for the beginning of January 2006. During the experiment, the temperature, pore-water pressure, gas migration, and deformation in the clay rock have been monitored by means of more than 80 instruments installed in 24 boreholes. Significant thermal effects have been observed. In the heated region at distances of 0.8–1.4 m to the heater, the pore-water pressure increased from 0.7–1.2 MPa to 3–4 MPa. The responses of the host rock in terms of pore-water pressure and deformation were simulated by several modelling teams with use of different codes. Preliminary results of the measurements and the calculations are presented.