Brenner pushes ahead with new contracts 21 Jul 2014

The next major phase of tunnelling on the Brenner Base Tunnel rail project has begun in the Alps between Austria and Italy with the Strabag and Salini Impregilo JV making an official start of excavation on its 55-month, €377.3 million contract for the mega project’s Tulfes-Pfons Lot. Located at the Austrian end of the €8.6 billion scheme (in 2012 prices), the Tulfes-Pfons Lot calls for a total of about 38km of drill+blast and TBM tunnel.

Impressive excavation of caverns at the Mauls adit junction with the main tunnels

Later in the same month (July 2014), the JV is to learn if its proposal among competitors will be confirmed as winner of another large contract for the estimated €300 million Isarco Underpass Lot.

While the scale and values of the two lots are substantial, the packages are to be followed by three even larger contract lots to complete the project. The client, Brenner Basis Tunnel (BBT-SE), which is a JV of Austrian and Italian rail companies, ÖBB and TFB, respectively, plans to start procurement for these final three largest lots in 2016, said Simon Lochmann, the Head of Communications for BBT-SE.

In April 2014, the Strabag-Salini Impregilo JV announced it was favourite for the Tulfes-Pfons Lot and Strabag, as the 51% lead partner, signed the contract with BBT-SE in June. Works commenced officially on 17 July with mobilisation underway for first excavation by drill+blast to start in September, and a TBM drive scheduled to launch in mid-2015.

Fig 1. Latest schematic of the 55km long Brenner Base Tunnel from the Innsbruck North Portal in Austria on the lower left to the Aicha South Portal in Italy in the upper right

The Tulfes-Pfons Lot has four areas of tunnel works:

• A 15km new section of exploratory tunnel;
• A 9.1km long safety/rescue tunnel;
• Two large connecting tunnels totalling some 9km in length; and
• A short extension of the twin main base tunnels by about 5km at the Ahrental adit area. In the overall project layout, the Brenner Base Tunnel scheme comprises an exploratory/drainage/service tunnel running between, and slightly below, the two main running tunnels for the full length of the project. The 8.1m i.d. running tunnels are 70m apart, linked by cross passages every 333m, and have multifunctional emergency stations, with access to the surface, at 20km intervals (Fig 1).

The geology on the alignment comprises quartz phyllite, slates, gneiss and granites with several identified faults and anticipated hydrogeological challenges. So far, a total of about 12km of the exploratory tunnel has been excavated along the main axis of the project in addition to a few short lengths of the main tunnels at adit junctions, said Lochmann.

Earlier drill+blast work at Wolf adit

The portions of exploratory tunnel built to date were undertaken in two sections, one located at each end.

At the north Austrian end, the Strabag/Porr JV completed drill+blast excavation of the section to the first adit junction at Ahrental.

At the southern Italian end, the longest exploratory bore advanced from Aicha (Aica). The 10.5km bore, which started off-line and reached the Mauls (Mules) adit between the main running tunnels, was excavated by Seli using a 6.3m diameter double shield TBM for the JV it was part of with Pizzarotti, Bilfinger Berger, Alpine Meyreder, Beton–und Monierbau, Jaeger, Collini and Societa Italiana per Condotte d’Acqua.

To extend the exploratory tunnel in the Tulfes-Pfons Lot, the Strabag-Salini Impregilo JV plans to use a 7.9m diameter TBM to drive southwards from the Ahrental junction towards the Wolf adit zone. When the new stretch is completed, just more than half the exploratory tunnel within the axis of the main running tunnels, will have been built. At the Ahrental adit and junction, the JV will also add short drill+blast extensions to the main tunnel headings.

Plan of works at the Mauls adit junction with the main baseline tunnels

The other works in the Tulfes-Pfons Lot relate to creating a link off the base tunnel, which will connect to the heart of Innsbruck. Two connecting tunnels will link the base tunnel with the existing, single tube trans-Alpine rail freight tunnel that bypasses the city of Innsbruck.

The bypass connecting tunnels will be larger than the standard size of running tunnels, explained Lochmann. BBT-SE, as designer of the scheme, said the different alignments of thee connecting tunnels, sweeping either over or under the alignment of the main Base Tunnels, prevents them from being linked by cross passages. As a result, and to provide safe zones along this stretch of the scheme, the tunnels are designed with a cross section of about 120m², and will have a concrete dividing wall running down their entire lengths to create the necessary secure safety zones.

Once the link tunnels merge with the rail bypass tunnel (Fig 1), and to prepare to carry passenger as well as freight trains, the existing tunnel will also need safety improvements. The design solution is for the safety/rescue tunnel to run parallel to the bypass tunnel. The safety tunnel will have a cross section of 35m² that will allow vehicles to pass, said BBT-SE in a statement. Excavation of this tunnel will progress from the Tulfes and Ampass access adits.

Early advance of the exploratory tunnel from Aicha to Mauls by a Seli TBM

Other works underway at mid-2014 for the project include extending the exploratory tunnel northwards by drill+blast from the Mauls (Mules) junction. Undertaken by a JV of Oberosler, PAC and Implenia the work includes excavation of TBM launch chambers for future lots, and a short advance of the main running tunnels. The drill+blast headings are in the largest fault zone identified on the project, the Periadriatic Seam, which is a tectonic plate boundary.

Works are also underway at the Wolf adit junction and at the Patsch ventilation shaft near Ahrental.

The main part of the Base Tunnel is 55km long between the Innsbruck and Fortezza portals. Including the existing bypass tunnel of about 9km long, the overall length of the main route infrastructure on the scheme is 64km. This constitutes the longest underground railway connection in the world, said BBT-SE. While freight trains will run at up to 120km/h through the link, passenger trains will travel at up to 250km/h.

BBT-SE expects to start procurement for two of the three remaining major lots in 2016, and of the third lot in 2018-19, said Lochmann. He added that due to the geological data from the early and exploratory works, especially at the Innsbruck end, it is now expected that most tunnel excavation could be by TBM with spoil removed via the advanced exploratory tunnel.

The schedule for the main lots is slightly later than anticipated back in early 2011. At that time, it was expected that tendering for these packages would start in 2015 for construction to begin in 2016. The project completion date is unchanged however, and a nudge upwards in cost is nominal due to the base year shift in published estimates.

The project is a transportation priority project for the European Union (EU), and while Austria and Italy are each funding 30% of the scheme, the majority of the 40% balance is being met by the EU. The project is to be completed in 2025 for operational services to begin by late 2026, said BBT-SE. As part of the key Berlin-Bologna rail transport corridor in Europe’s expanding rail transportation network, the Brenner Base Tunnel will eliminate the steep grades of the existing Brenner railway that was built in the 1860s.