On the thermal effects of mechanical behavior in the Callovo-Oxfordian claystone

The Callovo-Oxfordian (COx) claystone is investigated as host rock in the French project Cigeo for geological disposal of radioactive waste. Temperature rise due to heat emitted by radioactive waste is an important process to be considered. It is crucial to characterize effects of temperature change on the mechanical behavior of host rock. Despite previous studies, the issue is still open. This work presents a complementary study by performing a new series of triaxial compression tests. Six different values of temperature are considered ranging from 20 °C to 90 °C. The tests are performed under three different confining pressures. Elastic properties upon unloading–reloading paths and peak deviatoric stresses are evaluated for each test. It is found that the peak deviatoric stress of COx claystone is more affected by the temperature rise than the elastic properties. Scatters of experimental data are also investigated by comparing several tests performed under the same loading conditions. Finally, the thermal effects on the failure strength are evaluated by using a micromechanics-based criterion.