Micromechanics of Sheared Granular Layers Activated by Fluid Pressurization

Fluid pressurization of critically stressed sheared zones can trigger slip mechanisms at work in many geological processes. Using discrete element modeling, we simulate pore-pressure-step creep test experiments on a granular layer under sub-critical stress state to investigate the micromechanical processes stake during fluid induced reactivation. The global response is consistent with available experiments. progressive increase pore pressure promotes slow steady states, and fast accelerated dynamic once critical strength overcome. Our multi-scale analyses show that these two emergent behaviors correlate characteristic deformation modes: diffuse creep, highly localized rupture. Creep corresponds bulk while rupture results from grain rotations initiating overpressure unlocking contacts located within shear band which, consequently, acts as roller bearing for surrounding bulk.