Breakthrough under the Brenner

Breakthrough under the Brenner

The event was duly celebrated: the breakthrough in the so-called exploration tunnel of the Brenner Base Tunnel was celebrated with great pomp and fanfare in mid-September. Around 1,000 invited guests gathered in a tent near the border as the last meters of rock were penetrated underground via a live broadcast. Italy's Prime Minister Giorgia Meloni, Austria's Chancellor Christian Stocker, Transport Ministers Matteo Salvini and Peter Hanke as well as EU Transport Commissioner Apostolos Tzitzikostas pressed the symbolic red button together. There was great applause as tunnel workers walked together across the underground border between Austria and Italy.

In her speech, Meloni spoke of an “important step”. The tunnel connection would benefit the economy, competition and the environment in the future. The Brenner motorway, currently a “bottleneck”, will be relieved. Chancellor Stocker, however, was realistic: “The tunnel alone will not solve the transit problems.” The highway has long since reached its capacity limit. At the same time, he emphasized the need for “neighborly solutions” to traffic problems.

With the breakthrough of the exploration tunnel, a central stage in one of the largest infrastructure projects in Europe has been reached. The Brenner Base Tunnel (BBT) extends over a total length of 64 kilometers between Innsbruck in the north and Franzensfeste in the south. It is the heart of the new railway connection from Munich to Verona. Once scheduled for completion in 2031 and commissioning in 2032, it will be the longest underground railway connection in the world. Freight trains should be able to travel at up to 160 kilometers per hour and passenger trains at up to 250 kilometers per hour. The travel time between Innsbruck and Franzensfeste will be reduced from the current 80 to 25 minutes. The estimated costs for the project are an impressive 10.5 billion euros.

Technically, the BBT consists of three tubes: two main tubes in which the tracks run and a deeper exploration tunnel. This runs over a length of 57 kilometers and is around ten to twelve meters below the main tubes. The exploration tunnel was initially used for preliminary geological exploration and will later be used as a drainage, escape and maintenance tunnel. There are regular connections between the tubes at a distance of 333 meters.

“You can get from the exploration tunnel to the main tunnels at any time, which makes them usable throughout,” explains Sebastian Reimann, deputy project manager for the Austrian construction lot H53 Pfons–Brenner. "This brings advantages in terms of maintenance and repairs. Longer closures, such as the Gotthard Tunnel, are reduced as a result."

The choice of construction methods was based on the geological conditions. On the Austrian side, a combination of a tunnel boring machine (TBM) and the New Austrian tunneling method, i.e. blasting, was used. The first six kilometers of the exploratory tunnel were constructed using blasting from 2009 onwards. From the so-called Innsbruck emergency stop, the TBM “Günther” took over and drilled around 16.6 kilometers into the “Pfons-Brenner” construction lot. The remaining 8,500 meters to the state border were excavated using blasting. In total, the Austrian route consisted of six construction lots, the last one - H53 - was awarded to the Porr Marti consortium in 2023.

On the Austrian side, some geological challenges had to be overcome.  This included the “Iris” fault zone at kilometer 16.8: “A cavity of around 5,000 cubic meters was created there through unstable rock,” says Reimann. The tunnel builders had to stabilize this section with various measures, including foam injections, in order to enable the machine to pass through safely.

A second problem zone was in the Hochstegen area at kilometer 29. Here the tunnel crosses a permeable carbonate rock layer over a distance of 500 meters, which is highly water-bearing. The water shoots out of the rock here at a speed of up to 70 liters per second. In order to cross the area safely, extensive measures were also necessary here. “We drilled exploratory holes up to 120 meters deep, analyzed the rock and water conditions and then carried out targeted injections,” says Reimann. “The goal was to redirect the water and prevent it from entering the tunnel.” What was particularly sensitive was the fact that the area above ground is protected as a Natura 2000 area. The work was therefore carried out under strict official supervision.

In addition to the geological challenges, considerable logistical requirements also had to be overcome - in particular, the disposal of the excavated material required a lot of technical effort. "Between construction lots H41 and H53, an 18-kilometer-long conveyor belt was laid in the exploration tunnel. With additional sections, the total transport length was around 32 kilometers," explains Reimann. This conveyor belt was used to transport 3.6 million tons of material underground by 2 tunnel boring machines - this corresponds to around 180,000 truck trips that were avoided. “This is a major contribution to avoiding emissions, occupational safety and sustainability,” says Reimann.

But the work on the mega tunnel does not end there. Now it's time to finalize the two main tubes. The breakthrough is planned for 2026. The Brenner Base Tunnel is scheduled to be completed in 2031. It is scheduled to go into operation in 2032 – guaranteed with even more pomp and fanfare.

Information:

• Gesamtlänge: 64 Kilometer
• Struktur: Zwei Hauptröhren und ein Erkundungsstollen
• Funktion: Güter- und Personenzüge, reiner Zugtunnel
• Geplante Inbetriebnahme: 2032
• Kosten: rund 10,5 Milliarden Euro
• Bauzeit: seit 2007