ABSTRACT
The Tunnel Offenbau undercrosses a small mountain hill and is located between the existing highway A9 and the village Offenbau. The Tunnel was planned to built in open cut technique (Phase 1). Due to the difficult soft ground and groundwater conditions and the nearby village the tunnel had to be re-planned and was constructed by means of the top cover technique combined with compressed air as well as additional groundwater lowering in order to reduce the required air pressure (Phase 2).
