ROCK TUNNELS | PROJECT
BRENNER PASSES MAJOR MILESTONES
Rock tunnelling for the Brenner Base Tunnel project has delivered on key milestones over the last year, especially with bursts of celebrations in recent months for the Austrian-Italian high-speed rail transport link in late stages of construction in the Alps
IMAGES COURTESY OF BBT-SE UNLESS OTHERWISE STATED
For the best part of 20 years, the excavations for the Brenner Base Tunnel project in the Alps have been advancing, first with mobilisations and then small access and the early exploratory tunnel works before moving to open up the long, twin main rail tubes and various caverns, in different contract packages and to various scheduled timelines. Now the hard rock excavations are more than 90%
completed on the joint Austrian-Italian high-speed rail project. Main excavations continue on only one Lot while final lining works proceed elsewhere.
PROJECT PLAN The full Brenner project is 64km in length, most of which is the principal underground structure - the 55km-long Brenner Base Tunnel. An extra rail tunnel portion at the north end of the Austrian-Italian project will make the full Brenner link the world’s longest underground rail connection, says bi-national project developer BBT-SE. The Brenner Base Tunnel project layout comprises
twin 8.1m-wide, single-track main tunnels, running mostly parallel at 40m-70m apart, under a variable Alpine overburden of up to 1720m. The main tubes are connected every 333m by cross passages. In
22 | December 2025
addition, the long rail tunnel has three larger tunnel complexes that will be Emergency Stops along the long underground link. The Brenner tunnel configuration also includes a
narrower third tunnel, generally positioned between and about 12m below the main tubes. The exploratory tunnel helped to investigate geology along the route during planning and early construction phases of the main works; in future, during the operational phase of the rail link, the tunnel will provide drainage capacity and access/service capabilities. Aligned almost North-South, Brenner Base Tunnel
will be generally straight. Geology has large variations along the route and includes: quartz phyllite; Bunder slates (containing dolomites, quartzites, anhydrites, greywacke sandstone and other slates); gneiss; and, Brixner granites. There are also some fault zones, and the high overburden along the route presented some risk of squeezing ground conditions. At the ends, near the portals, the geology is variable again and there is much existing transport infrastructure. Brenner is a strategic link in the expanding European
network of high-speed rail links (TEN-T) and its design speeds for freight and passenger trains are 120km/h and 250km/h, respectively. The tunnel sits in
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