Influence of Chemical Degradation on Shear Behaviour of a Rock Joint - Application to CO2 Geological Storage

CO2 sequestration in deep geological formation is one way to reduce the greenhouse gas emissions causing global warming. Possible geological fault reactivation is an important aspect of site durability and must be considered. This phenomena stems from modifications of fault balance, such as new effective stress or chemical deterioration of fault roughness. This last situation defines the thematic developed in this work: analysis of the fault roughness modifications induced by a chemical degradation and their consequences on mechanic stability. The present study shows the evolution of the shear behaviour of an existing crack in Campanian Flysch specimens with chemical degradation. For that purpose, crack surfaces were immersed in an acidic solution ([HCl] = 0.6 mol.l-1) at a constant pH during 6 hours. A first analysis focused on the evolution of roughness parameters and material loss induced by chemical attack. Once degradation was characterized, direct shear tests on sound and chemically degraded samples were performed in the University of Sherbrooke (Québec, Canada). Classical curves of direct shear test (shear stress vs. Tangential displacement and dilatancy) of damaged samples show an important modification of the shear behavior : degraded joints have no shear stress peak and its contractance are more important.