The Brenner Base Tunnel - a new link through the Alps

14 As tunnel boring machines are very expensive and the preparation time before a machine can go into operation is much longer than than preperation time for drill and blast, the use of a TBM is only economically viable for longer stretches. Approximately 50% of the Brenner Base Tunnel is being built using mechanical excavation. In the process open TBMs (which install tunnel support using shotcrete, anchors and steel mesh) and shield TBMs (which install tunnel support using precast concrete tubbing rings) are used. The cutting head of a tunnel boring machine (TBM) is equipped with numerous drill bits. These crush the rock into small pieces that are then removed as spoil. The TBM in the Ahrental-Pfons exploratory tunnel is supplied by the so-called Multiservice Vehicle. excavation stabilization inner shell - reinforced concrete - tubbing ring lining clearance cable conduit pier wall drainage track drainage bottom tubbing segment ballastless track abutment water pipe – fire extinguishing system Mechanical excavation cross section mortar bed crack-resistant floor slab