Creep Effects on the Thermo-Hydro-Mechanical Responses of Callovo-Oxfordian Claystone

In France, a deep geological disposal for high-level radioactive waste (HLW) and intermediate level long life radioactive waste (IL-LLW) called Cigéo is planned to be constructed in a deep Callovo-Oxfordian claystone (COx) formation, if it is authorized. The heat emitted from the waste leads to a temperature increase in the low permeability host porous formation, which induces a pore pressure increase essentially due to the difference between the thermal expansion of the pore water and the solid skeleton. This study aims at assessing the effect of nonlinear behavior of COx, especially creep, on the THM response of the HLW repository. Different approaches, from perfectly MohrCoulomb model and simplified time-dependent models (power and Norton) to an advanced model, have been considered. These approaches lead to common conclusions that (1) the creep reduces the pore pressure increase compared to poro-elastic approach; (2) the nonlinear instantaneous response in the near-field resulting from cell drilling does not affect the THM response in the far field and (3) the thermal load does not induce any supplementary damage of the host rock