ABSTRACT
The rock strength surrounding the 27 km long water supply tunnel is too low for the overburden. The load bearing perimeter zones of the driven tunnel have first to increase by deforming. The tunnelling machine must be designed for the predominant geological conditions. The mechanical solution must, to a certain degree, also tolerate a deterioration of the geological conditions, while maintaining the production. The tunnel was to be driven using a Tunnel Boring Machines (TBM) which supported the unstable face with a bentonite suspension under pressure. On TBMs with fluid support, the crown remains the critical support area. During the operating mode, when the fluid support is effective, the crown is supported, even in the area of the rotating rim, because the suspension penetrates around the blade into the steerage gap and there maintains a predetermined pressure. The large modern TBMs with high torque and thrust forces require a more careful construction of the cutter head bearing and its seals.
