As tunnel boring machines are very expensive and the preparation time before a machine can become fully operational is much longer than the preparation 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 excavated using the mechanical method. In the process, open TBMs (which install tunnel support using shotcrete, anchors and steel mesh) and shielded TBMs (which install tunnel support using precast concrete tubbing rings) are used. Inner lining The concrete support structure is meant to last 200 years. As soon as the excavation and mucking operations are completed, the work of waterproofing the tunnel begins. Tunnel waterproofing involves the use of a protective drainage layer of geotextile fleece and an actual waterproof layer (fused plastic waterproofing strips). Once this is complete, the inner concrete lining is applied with a minimum thickness of 30 cm. Technical outfitting of the tunnel Once the construction work is finished, the ballastless track and the railway outfitting will be installed: the signalling and command and control systems, the telecommunications and monitoring systems, the ventilations systems, the doors and gates and all other technical systems including cabling and remote control systems. Annular gap backfill Clearance envelope Escape and rescue route Multi cable duct Sidewall drainage Track drainage Invert precast segment Ballastless track Abutment Service and maintenance path Waterpipe / Fire extinguishing system Steel-reinforced concrete - segmental lining Mechanical excavation cross section Mortar bedding Concrete slab Inner lining (if necessary) 19 BRENNER BASE TUNNEL
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