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.
The aim of the project is to find an explanation why elevation of the tunnel and the surface occurs in some sections in the Gipskeuper formation of the Chienberg tunnel, while in other, geologically similar sections, it does not. The understanding of these differences is very important for the restoration of zones with active rock swelling and for the planning of new tunnels in the Gipskeuper formation. We act on the assumption that the groundwater circulation and its changes at different scales play a major role in understanding these differences. Therefore, the project aims at reconstructing the groundwater circulation in the area of the Chienberg and evaluating its influence on the swelling phenomena in the Gipskeuper formation.
The following activities will occur:
- Accounting for the regional water balance
- Accounting geological profile in differently oriented sections and Fourier decomposition
- Stationary two-dimensional groundwater modeling taking into account the heterogeneity of mountain in different scales (regional, local) and the resulting in tunneling EDZ
- Identification of zones with increased water flow
- Simulation scenarios to study the influence of various geological structures and the EDZ
- Interpretation of results
The main outputs of the project are the following:
- Data bases for the study of coupled hydraulic-mechanical processes of rock swelling
- Implementation of the outcome in the planning and implementation of the reorganisation of Chienberg Tunnel
- Scientific basis for decisions when configuring tunnels in Gipskeuper and similar rock formations through improved understanding of the occuring processes