Similarities in the hydromechanical response of Callovo-Oxfordian clay and Boom Clay during gallery excavation

Several Underground Research Laboratories (URLs) in Europe have been dedicated to scientific programs to characterize the confining properties in clay layer geological formations in the frame of geological disposal of high level waste and spent fuel. The URLs are an integral part of national programmes as they provide the scientific knowledge necessary to be gathered in a safety and feasibility case (SFC). An important item for the long-term safety of underground disposal is the assessment of the extent of the damaged zone induced by both the excavation process and the thermal impact of the repository. The paper compares the hydromechanical response and the induced fracture patterns observed during recent excavation works performed at the Bure underground research laboratory in the indurate Callovo-Oxfordian clay and at the HADES underground research laboratory in the plastic Boom Clay. A comparison of the thermo-hydro-mechanical responses is given as well. Despite the important difference in their characteristics the observed thermo-hydro-mechanical response is quite similar for both types of claystone.