The first of two large tunnel boring machines (TBMs) for the Italian side of the Mont Cenis Base Tunnel, the central element of the future Turin–Lyon high-speed railway, has been officially handed over.

The machine was presented on 11 March 2026 at the Herrenknecht facility in Germany in the presence of representatives from project owner TELT, the UXT consortium (Itinera – agent, Ghella and Spie Batignolles Génie Civil), and project authorities.

The TBM will be deployed at the Chiomonte construction site in the Susa Valley, where it will first excavate the Maddalena 2 access tunnel before continuing with excavation of the southern section of the base tunnel towards Susa. Excavation on the French side of the tunnel is already underway.

Once the project reaches full tunnelling operations, seven TBMs will be working across the Italian and French sections, completing approximately 75% of the base tunnel excavation.

TBM specifications

The machine measures 235 m in length and features a 10.16 m diameter cutterhead.

Key technical features include:

• 13 electric motors producing a combined power of 4,550 kW
• Expected advance rates of approximately 10 m/day
• Segmental lining installed using hydraulic thrust cylinders

The TBM has been designed as a dual-mode machine capable of operating in both:

• Open mode for hard rock conditions
• Closed (slurry) mode for loose ground and sections below the water table

In slurry mode, excavated material is transported through a closed hydraulic circuit rather than by conveyor belt. The system incorporates:

• A crusher to reduce excavated rock size
• A pipeline system transporting a slurry mixture of water, bentonite, and spoil to the surface

To allow intervention in pressurised conditions, the TBM is also equipped with:

• Hyperbaric compression and decompression chambers
• A pressurised shuttle system enabling safe personnel access while maintaining excavation progress.

TBM design considerations

The machine design reflects the challenging conditions expected along the tunnel alignment, including:

• Complex geology
• Tunnel depths reaching up to 2,000 m beneath the mountain
• Tight horizontal and vertical alignment curves
• High natural rock temperatures identified during excavation of the Maddalena exploratory tunnel

These factors influenced the sizing and configuration of the TBM.

Chiomonte construction site (CO3/4 contract)

The Chiomonte site is the principal Italian construction base for the cross-border section of the project and has been designated a strategic national infrastructure site since 2012.

The works associated with the CO3/4 contract involve approximately 30 km of excavation, including:

• Two tubes of the Mont Cenis base tunnel
• The Maddalena 2 access tunnel
• Cross-passages between the main tunnels
• The Clarea underground safety facility
• An artificial tunnel at the eastern entrance to Susa

Excavation will be carried out using a combination of conventional methods and two dual-mode TBMs.

Site preparation

Preparatory works are currently underway to receive the TBM.

Recent milestones include:

• Completion of a new construction access junction from the A32 motorway, commissioned by Sitaf
• Construction of a Berlin wall bulkhead
• Planned lowering of the existing working platform

Conventional excavation will then proceed for approximately 160 m of the Maddalena 2 tunnel, creating the launch chamber from which the TBM will begin its drive.

The machine will now be dismantled for transport to Chiomonte, where it will be reassembled. Tunnelling is expected to begin in 2027, with the TBM scheduled to excavate approximately 10 km of tunnel towards Susa.

Project progress

Construction of the 65 km cross-border section between Susa (Italy) and Saint-Jean-de-Maurienne (France) is progressing on multiple fronts both underground and at surface sites.

The project currently employs more than 3,300 workers and includes:

• Two parallel railway tunnels
• Four access tunnels
• 204 safety cross-passages

As of 28 February 2026, more than 47 km of tunnels have been excavated, including over 20 km of base tunnel, representing around 29% of the total 164 km of underground works planned for the project.

Further information is available at www.telt.eu and for more information on the project go to  fr/11 and it/80 in the Tunnelbuilder archive.