Ungewohnliche geologische Verhaltnisse und deren Bewaltigung beim Vortrieb des Tunnels Fussen

The 1271 m long border-passing Fussen tunnel is the missing link of the German Freeway A7 and the Austrian Fernpass route B 314. In March 1996, during running excavation works, an unexpected groundwater inburst of 400 l/s occurred. Carrying out voluminous grouting measures immediately, the water inflow could be stopped. To give an explanation for this unexpected water inflow, the model of a collapse dolina has been worked out. The dolina must have developed due to heavy leaching of the originally gypsum bearing strata of the Raibl formation during the glaciation period, covering an area of approximately 100 m × 80 m at the surface. The burried dolina is surrounded by collapse breccias, which give a reference for the extremely steep walls of the sink hole at that time. As a consequence and in order to avoid further lowering of the ground water level in the Faulenbach valley, the tunnel had to be excavated within a protection shield of ahead-of-the-face-groutings at an overall length of 240 m. This method is unique in the history of NATM.