The second test site for the renovation of the Mont Blanc Tunnel vault will be carried out from 1 September to 12 December 2025 in two sections of the tunnel, upstream and downstream of one of the two sections renovated in 2024, approximately 8 km from the France entrance, for a total of 254 m. This project follows the first test site carried out from 2 September to 16 December 2024 on two sections of 300 m each. These works in 2024 and 2025 represent a total investment of EUR50 million.
The period was identified together with the Autonomous Region of Valle d'Aosta and the Prefecture of Haute-Savoie, considering autumn to be the period with the least impact on tourism, particularly for light vehicles, the primary users of the tunnel (75% of traffic in 2024), and on the economy between the two regions.
The type of work, the geometric characteristics of the tunnel, the need to dismantle all the technological systems in the areas of intervention (accelerators for controlling longitudinal air flow, cameras and automatic event detection, thermometric cable, etc.) and the safety of the workers do not allow vehicle traffic to pass under any circumstances, even temporarily, during the entire duration of the works. This project will require a total closure to traffic for approximately 15 consecutive weeks.
The Mont Blanc Tunnel is over 60 years old. It is the first of the major European tunnels to undergo extensive structural renovation work. In addition to the routine maintenance carried out during night-time work, this exceptional project is entering a period during which more significant civil engineering work is required. This major work on the infrastructure itself is necessary to ensure its long-term sustainability. Since the tunnel reopened in 2002, TMB-GEIE has been monitoring the vault and road deck on an annual basis. This permanent monitoring allows us to track its evolution over time and to define the future work to be carried out.
The nature of the works
The two sections of the tunnel affected by the works, located approximately 8 km from the France entrance, have already undergone preparatory work: dismantling of the wall cladding panels and their substructure, dismantling of lamps and installation of site lighting, installation of temporary anchors (5 m fibreglass nails).
The main activities will begin on 1 September:
- dismantling of the systems anchored to the vault and piers (accelerators for controlling longitudinal air flow, cameras, automatic event detection, thermometric cable, variable message signs, vertical signage, etc.),
- installation of dynamic containment to operate in protection mode against the risk of asbestos,
- precision milling of the structure optimised to 26 cm at the level of the keystone,
- demolition of part of the concrete vault,
- collection of water leaks and installation of drainage systems,
- complete waterproofing of the pier and vault,
- construction of the pier for the new 2.5 m high cast-in-place cladding,
- installation, adjustment and bolting of approximately 220 prefabricated reinforced concrete segments,
- injection of micro-mortar into the rear of the vault and sealing of the segments,
- reinstallation of safety systems, followed by a test phase before reopening to traffic.
The two test phases of experimental work in 2024 and 2025 will enable the best operating methodology for the future restoration of the vault to be identified, in particular the duration, the technology used, the long-term impact of the closure and alternative routes, etc.
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