TBM breaks through on Brenner exploratory tunnel

7 July 2020

Final breakthrough has occurred on the 16.5km-long exploratory tunnel of the Tulfes-Pfons section of the Brenner Base Tunnel (BBT), Austria. Following assembly inside a cavern 3.5km deep inside a mountain, the 7.9m-diameter hard rock, Herrenknecht open-gripper TBM (‘Gunther’) started mining on 26 September 2015 from Ahrental eastwards to Steinach, drilling through hard rock to break through on July 6 2020.

The exploratory tunnel extends the entire length of the Base Tunnel running around 12m below the main tubes. The route comprises a complex system of tunnels: in addition to the exploratory tunnel just completed, the Tulfes-Pons section has four other tunnels: a completed 6km-long main tunnel (70m2 cross-section); a 9.7km rescue tunnel; a 6.8km connecting tunnel and a 3.9km security and logistics tunnel already finished.

When finally completed, the 64km-long BBT will be the world’s longest underground rail link, extending from Innsbruck to Fortezza, Italy. Spaced between 40-70m apart, the twin, single-track tubes will be linked by cross passages located every 333m. The tunnel route is almost horizontal for the majority of its length, a huge advantage over the rising and falling of the existing 140-year-old line which crosses the Brenner Pass at 1,371m ASL.