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

Operational project 8, led by the Implenia consortium (lead contractor), NGE and Itinera, is responsible for excavating the first 5678 m of the entrance on the French side of the Lyon-Turin base tunnel, under the project management of TELT, for a total of €228 million.

After three years dedicated to the excavation of the two main tunnel tubes, the consortium Implenia (lead contractor), NGE and Itinera announces the entry into a new phase of the construction site: the creation of the final concrete lining. A specialized team is mobilized behind the mining face to carry out this operation. By the end of September 2025, 76% of the excavation of the tunnel entrance will be completed, i.e. more than 4.300 meters already excavated out of a total of 6.105 meters, including branches. This section is distinguished by the exclusive use of the traditional excavation method, without the use of a tunnel boring machine—a remarkable specificity across the entire cross-border route.

The final lining of the tunnel: a multi-phase project

The implementation of the final tunnel lining takes place in successive stages, according to a precise sequence:

Preparation of the support: re-establishment of the facing to receive the vaults, earthworks for the counter-vaults, re-establishment and repair of the support.
Construction of the counter-vault: waterproofing and reinforcement, concreting.
Installation of drainage networks: installation of networks and manholes, filling, diversion of networks in tunnels.
Construction of the vault: waterproofing with an automatic installation gantry, installation of reticulated arches and reinforcement in the arched areas and at intersections, concreting.

Tailor-made tools, designed for the health and safety of all

To optimize each phase of the work while guaranteeing a high level of safety for operators, two specific pieces of equipment were custom-designed in partnership with specialized companies:

KERN (Switzerland): for the design of the tool for lining the tunnel counter-vault
FORKAST+ (France): for the construction of the formwork for the tunnel vault and the lifting gantry.

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

The first tool, intended for the tunnel counter-vault, was received in March 2025 and put into service in May. It has already enabled the construction of 56 plots of 10 meters each.
The second tool, dedicated to the vault, was installed at the tunnel entrance in June and put into service in July, with the first definitive concrete ring being poured in August.

All the concrete used on the site is manufactured using a double plant dedicated to the project and installed on the work site.

These innovations demonstrate the project's commitment to combining technical performance, safety and operational excellence in the construction of this strategic infrastructure on a European scale.