A laboratory investigation of thermally induced pore pressures in the Callovo-Oxfordian claystone

In the framework of research into radioactive waste disposal, it was decided to investigate the thermally induce pore pressure occurring in the Callovo-Oxfordian claystone (a possible host rock in France). Thermal pore pressures appear in low permeability soils and rocks because the thermal expansion coefficient of water is significantly higher than that of the solid grains.Claystone samples provided to the laboratory are often desaturated, so particular emphasis was put on the saturation of the samples, carried out under in-situ effective stress condition.Thermal pressurization was investigated by performing undrained heating tests while measuring pore pressures changes in a specially adapted thermal isotropic compression cell. Special care was devoted to calibration procedures to account for the effects of the system on pore pressure measurements. The thermal pressurization coefficient measured appeared to change with temperature, mainly because of the changes with temperature of both the water thermal expansion coefficient and the drained compression coefficient of the claystone.