Laboratory and in Situ Simulation Tests of the Fracturing in the EDZ around Galleries in Opalinus Clay

Within the framework of the TIMODAZ project laboratory and in-situ experiments have been performed to study the failure processes around tunnels in laminated clay rich sedimentary rocks at reduced scale. The fracture patterns observed in the hollow cylinder laboratory experiment and in the borehole-scale in-situ experiment show great similarity. In both cases, cracks sub-parallel to the bedding planes open and lead to buckling failure if supporting structures in the cavity are absent. These observations emphasize the role of the mechanical anisotropy for the excavation damage and the short term changes in hydraulic properties in the nearfield of tunnels in anisotropic rock. Progress in understanding of these failure mechanisms may also open opportunities to optimize the support concepts for tunnels in such rocks.