For the Kramer Tunnel, located in the west of Garmisch-Partenkirchen, Germany a reconnaissance tunnel was excavated in advance. This was necessary, because very inhomogeneous and partly very bad rock conditions were assumed and because major sections of the tunnel could not be explored with drillings due to topographic conditions. In the paper, the lessons learned from the reconnaissance tunnel are described. It specifies how to deal with the high water pressure in the main dolomite area, which safety measures are necessary in the Kramer Reverse Fault area (squeezing rock conditions) and how the heading can be carried out in a little explored rockslide area.
Garmisch-Partenkirchen is a well-known touristic centre in the northern Alps in Germany. In order to reduce the traffic within of Garmisch-Partenkirchen a relocation of the federal road B 23 is planned. The ringroad will pass Garmisch-Partenkirchen to the west under the Kramer mountain massif in the so-called Kramer tunnel.
The design of the Kramer tunnel was carried out by the Staatliches Bauamt Weilheim and the ILF Beratende Ingenieure ZT GmbH, Innsbruck. The tunnel is designed as a single-tube tunnel with two-way traffic. With an axial distance of 45 m parallel to the tunnel tube a reconnaissance tunnel is excavated in advance which should be later used as a rescue tunnel. The construction of a reconnaissance tunnel was required in advance, since major sections of the tunnel could not be explored with drillings due to topographic conditions. Figure 1 shows a cross section through the traffic tube (main tunnel) and the rescue tunnel (reconnaissance tunnel) viewing to the south.
The reconnaissance tunnel as well as the main tunnel are planned as drained tunnels. Only in the rockslide area both tunnels will be covered with an total sealing in order to avoid a lowering of the ground water level in this area for reasons of nature protection.