Brenner moves on exploratory tunnels

The first contract for the exploratory bores on the Brenner Base Tunnel project has been awarded to a JV of eight companies for US$107.9M (excl VAT), and will involve driving a 10.5km tube with a 6.2m diameter Seli TBM.

On the Italian side of the Austrian-Italian rail project, the contract to bore from Aicha to Mauls will start by spring 2008 and all works should be finished within two years.

The contract is the first of four exploratory tunnels planned ahead of the twin main running bores for the Brenner Base Tunnel. Once completed, the four drives will have formed a single tunnel that will be used as a service tube that is positioned between, but below, the main tunnels.

Geology along the Aicha-Mauls drive is described as ‘very good’ being Brixner granite with some faults and groundwater expected in defined areas. About 40% of the drive is expected to be rock Class II and 50% is expected to be Class III.

Seli’s double shield TBM will be dismantled in a 200m-300m long cavern to be opened up using NATM at the junction with a 1.77km long access adit. NATM will also be used back at the launch portal to build a 400m long tunnel to remove spoil to the Riggertal deposit. The tunnel was wanted to avoid disturbing local communities.

The contractors in the JV are: Pizzarotti, Bilfinger Berger, Alpine Mayreder, Beton –und Monierbau, Jaeger, Seli, Collini Impresa Costruzioni, and Societa Italiana per Condotte d’Acqua.

The next exploratory tunnel contract being prepared is at the opposite end, on the Austrian side, which will be a 5.6km long NATM excavation mostly in quartz phyllite, rock Class III mostly, from Innsbruck to Ahrental. A 2.4km long access tunnel will be built at Ahrental by NATM for the contract. Depending on the final decision from the Austrian Transport Ministry on the need for an environmental impact assessment, the tender process could start as early as the end of this year.

To complete the entire exploratory tunnel there will be the final two drives closest to the border where the overburden will be up to 1600m. They will have the most difficult geology of all the exploratory drive, especially a 8km long zone under the border where the African and European tectonic plates meet, throwing up the Alps. One tunnel will be driven from the Austrian side, the other from the Italian side.

On the Austrian side, a NATM-driven 3.1km long adit at Wolf will enable drives of 7.5km and 5.2km in opposite directions – towards Innsbruck and Italy, respectively. Over on the Italian side, tunnelling works will involve a 13.1km long bore between Mauls and Pfitsch, and a 3.9km long adit.

The total length of the exploratory and adit tunnels will be 23.6km on the Italian side and 18.3km on the Austrian side. Phasing of the contracts will give geological data to enable stretches of the main tunnels to then proceed in phases. The main bores will have an excavated diameter of 9.6m, and plans for the first contract (Innsbruck-Ahrental) are to be submitted later this year, which may see construction start early 2010.