On September 17, 2025, just 600 meters before reaching the municipality of Saint-Martin-la-Porte, tunnel boring machine (TBM) Viviana completed a complex 90° rotation inside the tunnel to align with the base tunnel axis. Moments later, it began driving forward to excavate its assigned 9 km section of the Turin–Lyon railway base tunnel.
The Mont Cenis base tunnel, stretching 57.5 km beneath the Alps, is the centrepiece of the cross-border section of the new high-capacity rail line between Lyon and Turin. As part of the EU’s TEN-T Mediterranean Corridor, the project aims to boost sustainable transport, ease freight flows, and cut the environmental footprint of European logistics.
A Complex Positioning Operation
Unlike most TBMs that start aligned with their axis, Viviana had to be assembled in a side tunnel perpendicular to the base tunnel alignment. To start excavation, the 1,300-tonne machine was carefully rotated and repositioned through a series of precision lifting and shifting operations.
At the front sits the 10.4 m diameter cutterhead, followed by nine support trailers that are added progressively as the machine advances. Together, they form a 180 m long, 3,000-tonne “mobile factory,” equipped with cutting-edge technology for safe, accurate tunnelling in difficult Alpine geology.
A 15-person crew, working in three continuous shifts, operates Viviana. As the TBM advances, it installs precast reinforced concrete rings—each made of eight segments—to ensure long-term stability of the tunnel. Excavated rock is moved out by an integrated conveyor belt system, which both speeds up excavation and allows for efficient reuse of materials.
The site runs 24/7 and currently employs more than 1,300 people.
Who Built and Operates Viviana
The machine was manufactured in Germany by Herrenknecht and is deployed by CO6/7, an Italian–French consortium led by VINCI Construction Grands Projets, together with Webuild, Dodin Campenon Bernard, and Campenon Bernard Centre Est. Construction management is provided by SETEC, Systra, Italferr, and ARX.
Construction Site 6/7: A Key Section of the Base Tunnel
Construction Site 6/7, one of the largest along the Turin–Lyon route, covers 36 km of tunnel excavation between Saint-Martin-la-Porte and Modane. Work here combines traditional drilling and blasting with mechanized excavation using three TBMs.
Viviana will drive 9 km of new tunnel, parallel to the pilot gallery excavated in 2019 by TBM Federica. The other two TBMs at this site will later excavate the double-tube section between La Praz and Modane.
Progress on the Cross-Border Section
So far, over 44 km of the 164 km of planned tunnels for the new line have been completed—about 27% of the total. This includes 18.5 km of the Mont Cenis base tunnel.
Across France and Italy, 11 active worksites are underway, employing more than 3,000 people. At peak activity, up to 4,000 workers and seven TBMs will operate simultaneously. Four TBMs have already been delivered, and the first of the two machines assigned to the Italian side is currently under construction.
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