The Brenner Base Tunnel – A railway line for the future

Konrad Bergmeister, CEO at BBT SE

The Brenner Base Tunnel (BBT) is a straight, flat railway tunnel connecting Austria and Italy. It runs from Innsbruck to Tulfes/Fortezza and connects to the existing Innsbruck bypass. The 64km-long BBT under the Alps will become the longest underground railway infrastructure in the world.

The BBT is the centrepiece of the high-capacity railway line between Munich and Verona. At the same time, it represents the key element of the European Corridor No. 5 Helsinki–La Valletta which was previously the TEN T1 from Berlin to Palermo. The European Union supports the expansion of this transnational stretch and considers it a top priority.

The project

The Brenner Base Tunnel consists of two rail tunnels, each equipped with a single track. The distance between the tunnels is 70m for nearly their whole extension. Near the portals this distance decreases to approximately 4m. These two main tubes have an internal diameter of 8.1m, and they are connected at regular 333m intervals by cross tunnels which will serve as escape routes in emergency situations.

An exploratory tunnel will be located 11m below the two main tunnels. This exploratory tunnel, with an inner diameter of approximately 5m, is to be driven prior to the construction of the main tubes as it provides information on the geological and hydrogeological composition of the rock. This preliminary research will help to minimise both construction costs and risks. The exploratory tunnel will ultimately be completed throughout the main tunnels’ length, and will be used during operation as a drainage tunnel and, where necessary, as a service tunnel.

The most important technical parameters for the BBT are as follows:

• Total length: 64km
• Gradient: 4.0‰ to 6.7‰
• Altitude of the crown of the BBT: 795m above sea level
• Net cross-section of main tubes: Approximately 43m²
• Internal diameter of main tunnels: 8.1m
• Minimum cross-section of exploratory tunnel: 26m²
• Transverse-gallery spacing: 330m

The longitudinal gradient of the Brenner Base Tunnel is 6.7‰ on the northern side and 4‰ on the southern side of the Brenner. The apex height lies at 790m above sea level, which means that the tunnel runs more than 580m beneath the Brenner Pass (1,370m above sea level).

In total the Brenner Base Tunnel system will include approximately 230km of tunnels, considering the two main tubes, the exploratory tunnel running from one end to the other and all the lateral access tunnels and cross-passages. They will be excavated approximately 20% conventionally and 80% by mechanised systems.

Construction progress

Work is currently underway on three construction sites along the Brenner Base Tunnel project area: in Mules along the Periadriatic Seam in Italy, in Wolf and Patsch (near Innsbruck) in Austria. At the time of writing this article, 32km of exploratory and access tunnels have been excavated. The first 3km of main tunnel tubes have also been excavated in Mules. In summer 2014, two major lots will be launched – the Tulfes/Pfons section in Austria and the undercrossing of the Isarco River in Italy. With these two major construction lots the Brenner Base Tunnel has reached an investment of over €1 billion.

Periadriatic Seam

In Italy, the first construction lot of the Mules access tunnel and the first part of the exploratory tunnel in Aica (10.5km) have been completed. Construction continues northwards towards the Brenner Pass using blasting. This stretch crosses the Periadriatic Seam, a fault line, where the excavation work requires the greatest of care. The exploratory tunnel has passed this geologically complicated fault without major complications, so that the prevision for the main tubes, which are currently 1km behind the exploratory tunnel, is very optimistic. Three kilometres of the main tunnel tubes have already been excavated in this area. In the same lot several preparatory works have been carried out as well, such as the two 350m² caverns for the assembly of the tunnel boring machine for future drillings and several connecting and logistical tunnels. The spoil from the exploratory tunnel and the main tubes is transported via conveyor belts to the disposal area of Hinterigger at the portal of the exploratory tunnel. It is approximately 14km-long.

Wolf 2–Padaster

After the completion of the first 200m of the lateral access tunnel and the two logistical tunnels of Saxen and Padaster (the Padaster tunnel and the Saxen tunnel are both meant to serve construction site traffic) in the Wolf1 lot, the second phase of works to complete the 4km-long access tunnel started on 4 December 2013. The Wolf2 lot consists of the excavation of the mentioned access tunnel measured at 120m². The miners are advancing the tunnel with five blasts a day, so that the tunnel increases in length around 10m a day. The excavation works of the first 1,200m of the Wolf access tunnel have been completed. The excavation material is transported through the existing Padaster tunnel directly to the disposal area of Padaster valley.

The same lot includes a number of very important preparatory works for the disposal area. A tunnel of 1,500m-long is being built to relocate the Padaster River, in order to allow the future disposal of spoil in the valley. All these measures are meant to reduce traffic for the surrounding villages. Once spoil disposal is finished, the Padaster valley will be reforested and the Padaster River given a new streambed on the surface.

Ventilation shaft in Patsch

A 180m-deep ventilation shaft is being built in the township of Patsch. It leads from the surface straight down to the Ahrental access tunnel. This shaft, with a diameter of about 6m, is being built by blasting from the top down. It will be used for the ventilation of the tunnel system both during the construction phase and during the subsequent operation of the Brenner Base Tunnel. Construction work started in April 2014 and is planned to be completed in October 2014. The total cost of this lot is approximately €7 million.

Tulfes/Pfons

The call for tenders was announced in August 2013 and has been the largest announcement of the BBT SE so far. It covers 38km of tunnelling, namely the exploratory tunnel from Ahrental, continuing southward to the municipal area of Pfons, with a total length of about 15km, a 9.1km-long rescue tunnel along the existing Innsbruck railway by-pass and two connecting tunnels that will connect the Innsbruck by-pass with the two main tubes of the Brenner Base Tunnel. For the construction of the exploratory tunnel stretch an open tunnel boring machine (TBM) will be used for the first time in Austria. All other excavation work will be performed by drill and blast. Construction work will start in summer 2014 and last for approximately four and a half years.

Undercrossing of the Isarco River

About 1km north of Fortezza the Brenner Base Tunnel will cross under the Isarco River. There, besides the exploratory tunnel, the construction of the two main tubes crossing under the Isarco and two connecting tunnels to the existing railway lines between Oberau and Mittenwald are to be built. This project is quite a complex one as several preliminary works have to be carried out on the surface. The state road must be relocated and two bridges along the motor highway have to be built. Three 0.5km of tunnel will be constructed by blasting and 1.5km will be constructed by cut-and-cover. During construction the Isarco River and the existing railway have to be relocated. This lot amounts to €370 million. The tender for this lot is about to be awarded so that the first works will start in autumn 2014. The actual construction of the two main tubes is planned to be started in autumn 2015.

Costs and financing

The estimated costs for the Brenner Base Tunnel (as at 01.01.2012) amount to €8.585 billion, including risks that are presumed to occur but are not quantifiable. The costs are re-evaluated and carefully surveyed on a yearly basis. The major cost groups can be identified as follows:

• Civil work: 60%
• Rail and technical equipment: 15%
• Management costs and ground rents: 12%
• Risk contingencies: 13%

The financing of the Brenner Base Tunnel can be guaranteed by assigning approximately a third of the costs respectively to Austria, Italy and the EU.

Operation and traffic

The BBT is meant primarily for freight transport, allowing a modal shift of traffic from road to rail. Passenger trains can also travel through the tunnel. Thanks to the virtually horizontal tunnel, train traffic will no longer have to contend with the steep up and downhill slopes on the Brenner railway line that by now is over 140 years old.

The Brenner Pass at 1,370m is the lowest crossing point in the Central Alps and is passable all year round. Since man discovered the Alps as a habitat, it has always been used as a crossway. Nowadays, freight transport on the mountain stretch is difficult and complicated. Freight transport over the Brenner was recorded to be 41 million tonnes in 2013. The Brenner highway and the railway line are nearing their capacity limits. Only one third of freight transports is carried out by rail. Traffic simulations show that freight traffic will increase over time. Therefore, the call for a transnational solution for the traffic problem has been growing for decades.

The vision of a base tunnel surfaced repeatedly over the past century. The building of a new traffic route in the form of a new railway line over the Brenner has been the object of intensive studies and planning for decades. On a new Brenner railway line, heavy freight traffic between Munich and Verona should, in the future, travel underground as much as possible. The existing traffic infrastructures which run mostly aboveground should be used primarily for passenger traffic.

The basic premise of the 1987-1989 feasibility study for the Brenner Base Tunnel was mixed transport as an operative system with a capacity of 400 trains per day at the Brenner Pass, 80% of which are freight trains. Just like the other transalpine tunnels in Switzerland, the Lötschberg and Gotthard tunnels, the Brenner Base Tunnel is designed for mixed traffic.

The maximal speed of the stretch for freight trains was set at 100km/h in the feasibility study and at 250km/h for passenger trains. In the 1993 feasibility study the maximal speed of the stretch for freight trains along the stretch between Munich and Verona was raised to 160m/h.

Biography

Konrad Bergmeister has been the CEO of the BBT SE since August 2006. He was previously the Technical Director of the Brenner highway. For the past 15 years, Konrad has taught construction engineering at the University of Natural Resources and Applied Life Sciences in Vienna, and he has been the President of the Free University in Bolzano since 2010.