Brenner Base Tunnel, Austria, Italy
When completed in 2025, the 64 km long Brenner Base Tunnel (BBT) will be the world’s longest underground rail tunnel, traversing below the Alps from Innsbruck (Austria) to Fortezza (Italy). The tunnel will serve as the most important link in the Berlin-Palermo high-capacity rail axis, and is designed to shift freight transport from the roads to the rails. The Brenner Base Tunnel is financed under the budget of the Trans-European Networks (TEN), with support from the EU. The rail corridor will run flat at the base of the Alps, with two parallel tunnels connected at intervals of 333 metres. The line traverses below the 1,371 metre high Brenner Pass at an altitude of 794 metres – with a maximum slope of 6.6/1000.
The Gotthard Base Tunnel, which opened in 2016 and is currently the longest base tunnel at a length of 57 km, will be relegated to second place when the Brenner Base Tunnel opens. For Dr. Klaus Felsch of HeidelbergCement, specialist for transport infrastructure construction, even the Stuttgart 21 project with its 120 km of tunnels (to which the company is also supplying concrete) is minor by comparison. Namely, when all of the tunnel tubes required for the BBT project are added together, they total more than 230 km – of which 62 km have already been excavated.
“My job here is exceptionally challenging”, says engineer Martin Keinprecht. An understandable statement given the complexity of the tunnel system, comprising two 8.1 metre wide, single-track tunnels, running side-by-side at a distance of 70 meters apart. Every 333 metres, there is a passage connecting the two tubes, which can be used for evacuation in cases of emergency. A unique characteristic of the Brenner Base Tunnel is the “exploration tunnel” located between the two tunnels. It runs just 12 metres deeper along the full length of the BBT, and will be used long-term for drainage of the main tubes.
The current excavation work in this somewhat smaller tunnel (5-6 metres in diameter) provides even greater understanding of soil and bedrock composition than the previous core samples. That helps eliminate surprises, which might otherwise result in excavation stoppages that can cost up to EUR 40,000 per day. Because up to 70% of excavation for the BBT are to be performed by machine, six tunnel boring machines will be in operation simultaneously over the course of 2018. Ultimately, as many as nine of the gigantic drilling machines, which can excavate as much as 40 metres each per day, will be deployed.
An interactive route plan helps to keep track of excavation progress in the individual sections. Engineer Roland Murr is responsible for implementation of the project on the Austrian side. He works in tandem with the cement and concrete supplier, in consultation with the geologists, to determine the necessary injection mixtures prior to each new excavation phase. Different types of rock require different types of cement for tunnel stabilisation – for instance, cements with greater sulphate resistance. Account must also be taken of the increasing length of access tunnels. A quick hardening shotcrete is used to prevent cave-ins – but it must also remain workable for up to twelve hours, so that it doesn’t prematurely harden during the delivery.
In the exploration tunnel, a shotcrete layer is the finished surface. The special concrete mixtures used for this purpose are supplied by Munich-based Mobile Betonkonzepte via nine ready-mixed concrete trucks filled at various concrete plants surrounding the Brenner pass. The specifically formulated cements for the shotcrete production are procured by managing director Hans-Peter Haid from Rohrdorfer Zement’s Eiberg plant – a joint venture with HeidelbergCement. In total, more than 100,000 tonnes of cement will be delivered by the time the tunnel project is completed.
On the Italian side, HeidelbergCement’s subsidiary Calcestruzzi is delivering ready-mixed concrete to the Brenner Base Tunnel as part of the consortium “San Francesco”. The cement is produced by HeidelbergCement’s subsidiary Italcementi.
From the central hub in Ahrental, civil engineer Anton Ertl (a foreman on the BBT project) drives several kilometres to the particularly interesting Tulfes-Pfons section. Here, excavation work is ongoing round the clock to complete a total of 38 km of tunnel by early 2019. Like a snapshot of the progress along the way, the Tulfes-Pfons section is simply a component of the larger project, which takes shape bit by bit as the various sections are completed.
Strabag is operating on its own in this section with 350 workers – 40 of whom are involved in management of the project. Within a tight space, key tunnel elements converge, all under the direction of Anton Ertl: the nine kilometre Tulfes emergency shaft, the connection to the Ahrental access tunnel, the Innsbruck emergency station with central shaft and ventilation ducts, the two main tunnel tubes, one connecting tunnel, and the Ahrental-Pfons section of the exploration tunnel. To further complicate matters, the rail line has to switch from a left-hand to right-hand configuration south of Innsbruck, because of the different rail traffic systems used in Austria and Italy. The crossover is located shortly before Innsbruck, with a vertical clearance of only four metres.
To cut the 15 km segment of the exploration tunnel in this project section, a 200 metre long, 8 metre diameter open gripper tunnel boring machine from southern Germany’s Herrenknecht began excavation in 2015, and will continue tunnelling towards the south until early 2019. The emergency shaft will run the entire length of the 9 km Innsbruck Bypass. It is being blast excavated from three directions simultaneously. The 3 km of main tunnel tubes being constructed by Anton Ertl and his crew, as well as the connecting tunnel between the BBT and the Innsbruck Bypass are also being blast excavated according to the “New Austrian Tunnelling Method” (NATM).