Measurement of thermally induced pore water pressure increase and gas migration in the opalinus clay the HE-D experiment at the Mont Terri rock laboratory

In order to gain a better understanding of coupled thermo-hydro-mechanical processes in indurated clays as host rock for the disposal of high-level radioactive waste, a heating experiment named HE-D is being conducted by Andra, GRS and other partners in the Opalinus clay at the Mont Terri Rock Laboratory in Switzerland. Two electrical heaters were installed in a horizontal borehole of 30 cm diameter and 13 m length drilled from the HE-D niche parallel to the existing MI niche. Since April 2004, the surrounding rock has been heated by electric power input of 650 Watt in the first heating phase and 1950 Watt in the second phase. A third heating phase may be carried out for reaching a maximum temperature of 150 C at the interface between heater and rock, depending on the conditions of the testing equipments. Finally, after heater shut-down, the rock will cool down to ambient temperature. To observe responses of the clay rock to the thermal loading, a large number of measuring instruments was installed in the near field around the heaters to measure temperature, pore water pressure, gas migration and deformation of the clay during the experiment. For the design and interpretation of the experiment, numerical modelling work was conducted by different institutions using different codes. This paper presents results of the in-situ measurements of temperature, pore water pressure and gas migration in the clay rock during the experiment. (author)