Modelling clay rock behaviour from macro to micro scales (and back): deformation, rupture, and hydromechanical phenomena.

The long-term management of high-level nuclear wastes is envisaged by deep geological repository. In this context, clay rocks are considered as favourable media for deep geological repositories. Due to the safety function of the host formation, the behaviour of the Excavation Damaged Zone (EDZ) that develops around underground galleries during their drilling is of paramount importance. The EDZ is dominated by fracturing process which engenders irreversible modifications of the hydro-mechanical properties of the porous rock. In this zone, a significant hydraulic permeability increase of several orders of magnitude is observed. It may alter the safety function of the host formation by creating preferential flow paths for the migration of radionuclides towards the biosphere. Consequently, the understanding and the prediction of the EDZ hydro-mechanical behaviour are crucial issues for the long-term (safe) management of nuclear wastes. Among the different low-permeability media that are envisaged for the deep repository, the Callovo-Oxfordian claystone is studied. Moreover, it is well known that large-scale phenomena (deformation, failure, hydromechanical coupling …) take their origin from small scale processes (at grain and pore scale). Argillites are complex clay rock exhibiting a multi-scale heterogeneous microstructure. Questions have risen on how microstructural characteristics of heterogeneous rocks can enrich the constitutive behaviour at macroscale, in order to predict deformation and failure processes for instance. Consequently, the modelling of the hydro-mechanical behaviour of a clay rock is considered by taking into account its microstructural characteristics and their variabilities.