To study the effects of fracturing in the context of the Callovo-Oxfordian claystone and the proposed use of beds of this rock for a nuclear waste repository (ANDRA) we have developed a model that is implemented in the Cast3m finite elements code. This model couples (poro)elasticity, plastic deformation, damage through cracking at the micro-scale, reversible opening of macro-scale cracks, diffusion of water (and air) with associated changes in degree of saturation (and pore pressure), and swelling of clay minerals in a single, continuous model. Spatial variations in material properties, such as bedding planes, are considered by mapping them onto the mesh. Crack opening is calculated on the basis of previous studies [1], [2].This model is able to account for he effect on induced porous pressure on fracking. The model is compared with experiments carried out in the laboratory for the problem of gas fracturing.