In France, the National Radioactive Waste Management Agency (Andra) built the Meuse/Haute-Marne Underground Research Laboratory (MHM-URL) in the Callovo-Oxfordian (COx) claystone formation. The objectives of this URL is to assess the feasibility and safety of an industrial radioactive waste repository (Cigéo) and now to optimize different components of Cigéo. A thorough scientific research program, including specific in situ experiments, laboratory tests, both constitutive and numerical modellings, has been undertaken to characterize and to understand the thermo-hydro-mechanical (THM) behavior of the COx claystone. Based on experimental data, a constitutive model including, anisotropic elastoplasticity, damage and viscoplasticity is proposed to describe the hydromechanical behavior of this rock. This model has been implemented into Comsol Multiphysic© software and then applied to GCS drift.