Thesis: The safety assessment of a radioactive waste disposal facility installed in very low permeable clay rocks is one of the major issues this thesis aims to contribute. We focused on studying, through the SPH method, the mechanical response at the pore-scale of the Callovo-Oxfordian clay (COx) in a coupled phenomenon related to the gas migration.An in-depth study of solid material response through SPH solver was proposed. Small and large deformations were considered, where for the latter, a Total Lagrangian version was implemented through the Saint Venant-Kirchhoff constitutive model. First, an investigation for finite values of the SPH kernel support length was performed, which allowed characterising higher-order effects (also called non-local effects). The non-local effects appear to be directly related to the support-length parameter, which is purely numerical (and inherent to the SPH). We also proposed a non-local SPH-based approach to compute damage and fracture. The width of the localised damage zone is independent of the discretisation, and it is related to the kernel support-length. In quasi-static simulations, it was observed that the fracture propagation, which follows the damage localisation, was accompanied by an increase of kinetic energy and the discontinuity of the displacement fields.A set of SPH drainage simulations within a realistic porous material (COx clay) was proposed. The drainage led to the pore-space dilation during gas percolation. We showed that different confining pressure can affect the onset of fracturing with new pore space creation and also that initially isolated pores can be connected generating new percolating pathways.