Long-term anisotropic hydro-viscoplastic modeling of a drift at the Meuse/Haute-Marne URL

In the context of radioactive waste management, one of the options currently being considered is to store it in deep geological formations. Clay formations, in particular, show very favorable confining conditions as repositories for long-term safety of nuclear waste due to their low hydraulic conductivity and significant retention capacity for radionuclides. In France, the National Radioactive Waste Management Agency (Andra) began to build the Meuse/Haute-Marne underground research laboratory (MHM-URL) in the Callovo-Oxfordian (COx) claystone formation, lying between depths of 420 m and 550 m. With regards to the main objectives of feasibility and safety assessment of a potential deep geological repository (Cigéo), a comprehensive scientific research programme of specific in situ experiments, laboratory tests and numerical modelling have been carried out to characterize and understand the behavior of the COx claystone formation in the framework of hydromechanical (HM) processes (Armand et al. 2017). In addition to the HM couplings and the associated parameters, it appears necessary to consider at least the inherent anisotropies (mechanical and hydraulic) of such rock, but also its time-dependent behavior (Armand et al. 2017). In this paper, we consider the transient creep mechanism determined from laboratory tests in order to study its effect on anisotropy and hydromechanical behavior of COx clay. The hydromechanical couplings are then evaluated around the GCS drift of MHM-URL (drift excavated following the major principal stress and without rigid lining) under satured conditions using Comsol Multiphysics code