03/02/2025
Soletanche Bachy France contributes to the modernization and securing of the Nice-Breil railway line!
Since mid-September 2024, SNCF Réseau has mandated the consortium of Colas Rail, Soletanche Bachy France, La Nouvelle Sirolaise de Construction, CAN, and Hydrokarst to carry out modernization works on the tracks, reinforcement of engineering structures, and strengthening of tunnels. The objective is to improve mobility in the region of the Nice-Breil railway line.
As part of the State-Region Plan Contract (CPER), the section of the line between Drap and Breil-sur-Roya will undergo a major regeneration and securing program. The plan includes the consolidation and stabilization of existing engineering structures along the route.
Works planned for 2024 and 2025
Between 2024 and 2025, the line will be completely closed to carry out the following works:
- Modernization of 12 km of railway track;
- Reinforcement of 4 engineering structures, rail bridges, and 12 earthworks;
- Strengthening of 2 tunnels to ensure their durability (Engineering Structure Works).
Tunnel of Col de Braus
The Col de Braus Tunnel, 6 km long, crosses in its last kilometer terrains with anhydrite that are relatively sensitive to water. The progressive hydration of the massif has caused structural disorders in the structure and the platform for many years, increasing the constraints in the masonry. Most of the work to be done is concentrated in this tunnel.
Reinforcement works
The engineering structure works mainly consist of reinforcing the tunnel structure altered by a 15 cm thick shotcrete shell over 356 linear meters and along the vault. Over 1 km of works, Ziegler-type decompression niches are used to reduce ground constraints. Over time, the walls between the niches crack and will be reinforced with C60/75 reinforced concrete. The niches will also be cleaned, reshaped, and reinforced with shotcrete to prevent water stagnation.
Hydraulic works
Water management is crucial in this tunnel, especially with the presence of a potable water source that supplies the village of Sospel. The source water is channeled into a cast iron supply pipe, and the surplus into an open leaking aqueduct of 1300 linear meters, which will need to be diverted into a temporary pipe and then removed. Additionally, the effects of time and water infiltration have created decompression zones under this structure that will need to be injected.
A treatment campaign for dissolution zones is planned for certain parts of the structure. Finally, the shell will be drained, and the water evacuated outside the tunnel through lateral gutters over 1700 linear meters to be installed under the track ballast shielding.
Tunnel of Mont Grazian
This 4 km long tunnel is the smaller sibling of the Col de Braus. It is also affected by damage related to the presence of moisture and the superficial erosion of the facing concrete along the entire length of the tunnel. However, the volume of work is less significant:
- 15 cm deep rescindment with localized repair by shotcrete over 500 m² in the vault and sidewalls;
- Injection of diagonal and longitudinal cracks with stitching;
- Removal of detached coating with rejoining in search.
Site organization
All works are carried out on a single track from the rear base at Sospel Station, requiring precise planning to avoid blockages. A work train with 2 locomotives, 14 wagons, and rail-road machines (basket and excavator) is used for both tunnels, allowing the creation of several workshops along the route.
