Last month saw the deadline for tenders for the construction of the 7km-10km long Venaus exploration tunnel near the border between France and Italy.
The first kilometre of the 6m (approx.) diameter tunnel will probably be constructed using drill and blast, with a TBM excavating the rest. Geologically, the area is characterised by outcrops of two of the main lithostructural domains, the Piemontese Unit and the Briançonese Crystalline Massif of Ambin.
The Venaus tunnel is the third of four exploration tunnels that will be constructed on the massive 52.7km long twin-tube base railway tunnel alignment (presently un-named) between Saint-Jean-de-Maurienne, France, to the Suse valley, Italy. This, in turn, forms a vital part of the planned 280km long Lyon-Turin high-speed rail link.
The rail link is split into three sections: a French section, and Italian section and an international section. The domestic railway operators are responsible for the sections on their territories (which also include tunnelling works), while Lyon Turin Ferroviaire (LTF) was created in October 2001 to undertake a detailed study into the central international section. It is this part that includes the 52.7km long tunnel, and a 12km long tunnel between Venaus and Bussoleno. LTF is tasked with surveying the route, undertaking the physical feasibility study, and preparing the business case. The final decision on whether or not the tunnels will be built will probably be made in 2007. The European Union is partly financing the project.
Construction is already under way at Modane, at the base tunnel’s halfway point. Here, two contracts comprise a 4km long access tunnel, with a cross-section ranging from 65m2 to 80m2, and a 2.5km-3km long investigation tunnel, with a cross-section of 29m2-37m2. A joint venture between Eiffage, Condotte d’Acqua, and Granulats Rhône-Alpes won both contracts, worth approximately US$92M, and had excavated 651m by the end of July 2003.
Similarly the 2km long Saint-Martin-la-Porte access tunnel, with a 80m2-100m2 cross-section, is situated 7km from the western portal, where construction recently started. Work is also being carried out on the related 3km long investigation tunnel, which has an optional 800m drive, and a cross-section of 32m2-43m2.
The next tunnels to come up for tender, following the Venaus tunnel, are the La Praz access tunnel and investigation tunnel. Located about 20km from the western portal, the 2.7km long access tunnel will have a cross-section of about 80m2, while the 5.3km long exploration tunnel will have a 30m2 cross-section.
The high-speed link should help relieve one of Europe’s most congested transport corridors.
