ABSTRACT:

The 1271 m long cross-border Fuessen 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 ground water inburst of 400 l/sec occurred. Voluminous grouting measures were then required to stop the water inflow. To explain this unexpected inflow, the model of a collapse dolina has been forwarded. The dolina is believed to have developed due to heavy leaching of the gypsum bearing strata of the Raibl formation during glaciation, covering an area of app. 100 × 80 m at surface. The burried dolina is surrounded by collapse breccias, which provide a reference for the extremely steep walls of the sink hole. 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 protective shield of pre-grouted rock over a total length of 240 m..

GEOLOGICAL AND HYDROGEOLOGICAL CONDITIONS

With a total length of 946 km, the Federal Freeway A7 is one of the most important transit routes in Germany. The 1.2 km long, border-passing tunnel of Fuessen at the very south of the A7 is the connection to the Austrian "Fernpass" route B 314 (Figure 1). Table 1 provides a listing of important project data of the Fuessen tunnel. The project area is situated in the northern alps in the Falkenstein mountain range in a sedimentary sequence consisting of a dolomite formation (Hauptdolomit), a carbonatic, clastic and evaporitic formation in the "Faulenbach" valley (Raibl formation) and a solid limestone (Wettersteinkalk; see Zacher, 1966). For the first 500 meters, the tunnel cuts through heavily jointed and water-bearing Hauptdolomit with a maximum rock cover of 160 m (Figure 2; Thuro et al., 1997).

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