Lessons learned from the heading of the reconnaissance tunnel for the Kramer Tunnel, Germany

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.