TBM-S without active support at the limits of its capabilities / TBM-S ohne aktive Stützung im Grenzbereich der Anwendung

Three tunnels in the Perschling tunnel chain were driven successively by one TBM-S. In the course of the first two drives, there were many situations when the TBM-S without active face support was at the limits of its capabilities. The last tunnel to be driven was the Raingruben Tunnel with a length of 2,100 m. Based on the experience from the first two tunnels, advance ground improvement measures like grouting and groundwater lowering were undertaken in areas expected to be difficult. The measures meant that the drive could pass through the problem zones successfully. After about two thirds of the tunnel length under about 40 m of overburden, there were repeated collapses of the face. These reached a sudden peak with a major collapse of the face with an overbreak 34 m high above the crown, which extended almost to the surface. This blocked the cutterhead and the drive was stopped for five months. Various measures were undertaken in many stages to permit the TBM to restart. On account of the ground improvement works carried out from the surface, the remaining stretch was successfully bored and the tunnel structures of the Perschling chain were completed on schedule.