Multi-scale modelling of permeability evolution in the excavation damaged zone around tunnels

peer reviewedA zone with significant irreversible deformations and significant changes in flow and transport properties is expected to be formed in indurated clay around underground excavations. The stress perturbation around the excavation could lead to a significant increase of the permeability, related to diffuse and/or localized crack propagation in the material. The main objective of the study is to model these processes at large scale with a micromechanical damage approach, based on the Ponte-Castaneda and Willis approximation (PCW) in the presence of initial stress, in order to assess the crack impacts on the performance of radioactive waste geological repositories. Combined with this model, permeability tensor is described as a function of micromechanical damage that is generated during the excavation. Advantages and drawbacks of this approach are described thanks to the results on Opalinus Clay and of the Selfrac long term dilatometer experiment