During construction of the Chienberg tunnel, swelling phenomena associated with elevation of the tunnel and the surface occurred at two sections in the Gipskeuper formation. At other places with geologically similar sections such phenomena do not occur. Groundwater circulation plays a major role in understanding these differences. The proposed research project is designed to investigate the regional and local groundwater circulation systems and to link them to the occurring swelling phenomena. For this purpose, the distribution of hydraulic head, flow paths and volumetric flow shall be determined by a 2D groundwater model considering different scales and spatial orientations. The hydrogeological studies aim at defining the relations between surface hydrology, subsurface inflows, morphology and geological structures for the area of the Chienberg. The overall aim is to contribute to a better understanding of the complex coupled hydraulic-mechanical and geochemical processes that occur during rock swelling in sulfate-bearing clay rocks by characterising the hydrogeological regime.
The project is a part of a research cooperation between the ETH Zurich and the University of Basel, investigating the swelling activity in the Gipskeuper formation. The results can lead to recommendations concerning measures in the Chienberg tunnel and provide a scientific basis for decisions during project planning, cost planning and realisation of future construction and restoration projects of tunnels in the Gipskeuper formation.