Lyon–Turin Base Tunnel: Implenia, NGE and Itinera reach a key milestone with the completion of the first vault of the final lining on the French side.

After three years dedicated to excavating the tunnel’s two main tubes, the Implenia (lead partner), NGE and Itinera consortium announces the start of a new phase of the project: the construction of the permanent concrete lining.
A specialized team has been mobilized behind the excavation face to carry out this operation. By the end of September 2025, 76% of the tunnel entrance excavation will be completed — that is, over 4,300 meters already excavated out of a total of 6,105 meters, including connection galleries. This section is notable for the exclusive use of the traditional excavation method, without the use of a tunnel boring machine — a remarkable feature across the entire cross-border route.

The permanent lining of the tunnel: a multi-phase process

The installation of the tunnel’s permanent lining is carried out in successive stages, following a precise sequence:

• Support preparation: finishing of the surface for vault installation, excavation of the invert, reconditioning and leveling of the support.
• Invert construction: installation of waterproofing and rebar, followed by concreting.
• Installation of drainage networks: laying of networks and manholes, backfilling, and redirection of tunnel utilities.
• Vault construction: installation of waterproofing using an automated installation gantry, placement of reticulated ribs and reinforcement in curved areas and intersections, and concreting.

Custom-made equipment designed for health and safety

To optimize each construction phase while ensuring a high level of safety for all operators, two custom-designed pieces of equipment were developed in partnership with specialized companies:

• KERN (Switzerland): for the design of the equipment used in the tunnel invert lining.
• FORKAST+ (France): for the construction of the tunnel vault formwork and lifting gantry.

The design and development of these tools required nearly 12 months of intensive collaboration, driven by seven main objectives focused on working conditions, safety and ergonomics: ease of assembly and disassembly, accessibility, circulation on the equipment, workstation ergonomics, tool handling, maintenance, and task automation.

• The first tool, designed for the tunnel invert, was delivered in March 2025 and commissioned in May. It has already enabled the construction of 56 sections of 10 meters each.
• The second tool, dedicated to the vault, was assembled at the tunnel entrance in June and put into service in July, with the pouring of the first permanent concrete ring in August.

All concrete used on site is produced by a dual batching plant dedicated to the project and installed directly on site.

These innovations demonstrate the project’s commitment to combining technical performance, safety and operational excellence in the construction of this strategic European infrastructure

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Key figures for the CO08 site:

• Contract value: €228 million
• 5,678 meters of tunnel to be excavated
• 11 connection galleries
• 100% traditional excavation method
• 3 km conveyor belt
• 350 workers mobilized

Under the management of TELT (Tunnel Euralpin Lyon–Turin), the unique cross-border section of the Lyon–Turin project is divided into 9 operational construction sites: 4 on the Italian side and 5 on the French side.
Operational Site 8 (CO8) corresponds to the entrance of the base tunnel on the French side and the first few kilometers between Saint-Julien-Montdenis and Saint-Martin-la-Porte.
As of September 1, 2025, the cross-border section had already achieved 44.2 km of excavated galleries, representing 27% of the total, with more than 3,000 people working across the sites.