Lessons Learned in Plastic Clays

The hydro-mechanical response and the fractures pattern around excavations in Boom Clay is now well characterised. The water content influences strongly the behaviour of plastic clays and controls the fracturing, self-sealing and self-healing processes. Fractures are developed during the excavation. Their extent can be limited using appropriate excavation methods. After closure and full saturation of the repository system, it can be assumed that the remaining fractures will close progressively. The construction of the connecting gallery at Mol has shown that displacements and pressure in the host-rock can be predicted with a good confidence level. However additional efforts are needed to explain the observed hydraulic disturbance at a distance of several tens of metres. Fracturing and self-healing processes are currently studied within the SELFRAC project. The relevance of the EDZ to performance assessment is briefly discussed.