In the context of the the Swiss site selection process for nuclear waste repositories (Sectoral Plan), the Swiss Federal Nuclear Safety Inspectorate (ENSI) and the Swiss Expert Commission for Nuclear Waste Disposal (EGT) are engaged in geological, rock mechanical and engineering questions related to the construction and long-term safety of high-level and low- to intermediate-level nuclear waste repositories in the Opalinus Clay and similar clay-rich rocks. Of special importance are rock mechanical properties and boundary conditions (e.g. in-situ state of stress, depth, and excavation geometry), rock mass behavior, suitable engineering measures, and uncertainties related to the anticipated geological, mechanical and hydromechanical conditions.