The Brenner Base Tunnel - a new link through the Alps

12 Mechanical or conventional? – Different excavation methods are being implemented to build the Brenner Base Tunnel. The choice of excavation method depends on the geology of the mountain, on geotechnical findings and forecasts, and on construction logistics and economic considerations. The length of the route to be excavated and the available construction time, both influence the choice of tunnelling method. So some sections of the tunnel are excavated by drilling and blasting whilst others are built using continuous construction methods, such as with a tunnel boring machine (TBM). Excavation methods Conventional excavation using shotcrete is a very flexible method of excavation. This is suitable for difficult, varying ground conditions and is very good for different sizes and for complex cross-sectional geometries. Due to the complex excavation requirements, some sections of the main tunnel and exploratory tunnel, the two connecting tunnels in Innsbruck, all of the access tunnels, ventilation and logistics caverns, the connecting tunnels, emergency stations and cross-ways are being excavated using the so-called conventional excavation method, meaning by blasting (full and partial surface breakout) with shotcrete support. The stages for drilling and blasting are predetermined. The blast holes are drilled first, then loaded with explosives and finally, the explosion takes place. Once the breakout material has been removed, a process known as muck- ing, tunnel support is applied in the form of shotcrete, anchors, lattice arches and reinforcement mats. After one blasting cycle is complete, the process starts all over again. During the construction of the Brenner Base Tunnel blasting will take place every three to six hours depending on the geological composition of the rock. Conventional or drill-and-blast excavation bench excavation crown excavation crown stabilization excavation drilling jumbo mobile concrete spraying machine drilling jumbo wheel bearing fresh air supply rock anchor dumper concrete mixer truck Conventional or drill-and-blast excavation