16/01/2026
Soletanche Bachy France takes part in the rehabilitation of the Gustave Roch collector in Nantes
Nantes Métropole has entrusted the SADE / Soletanche Bachy France consortium with the rehabilitation of the stormwater collector on the Île de Nantes. Extending over 445 meters, this cast-in-place, unreinforced concrete ovoid structure is one of the key components of the city’s hydraulic network.
Works began in early October 2025, in the heart of a complex environment, in the immediate vicinity of the construction site of the future Nantes University Hospital (CHU), requiring close coordination and enhanced monitoring.
Project objective: strengthen, regenerate, and ensure long-term durability
The intervention aims to reinforce the existing structure through the injection of a cement-based, very low-carbon EXEGY® grout (70% CO₂ reduction on the project) combined with bentonite, providing both bonding and regenerative effects.
The operation includes:
• 1,069 drillings and 321 re-drillings
• A total volume of approximately 134 m³ of EXEGY® grout by Soletanche Bachy injected
• More than 1,000 drilling points breaking through to the extrados
• An overall objective of securing and extending the service life of the structure
This strict protocol is a major lever for maintaining the collector’s performance while avoiding heavy reconstruction operations.
Methodology and technical innovation
Injections are carried out in rings spaced 1.5 meters apart, each consisting of six drillings distributed:
• At the base of the sidewall
• At mid-height of the sidewall
• In the crown
The equipment used, specifically developed by Soletanche Bachy, allows precise monitoring of injection pressures and volumes to ensure uniform and controlled treatment. The injection plant layout was designed to treat all sections without intermediate relocation, thereby reducing disturbances and optimizing timelines.
A demanding project in a dense urban environment
Several major constraints characterize this operation:
• Continuous co-activity with the Nantes CHU construction site
• Ongoing monitoring of water levels in relation to tides, floods, and rainfall events
• A confined environment requiring extensive safety and prevention measures
The work carried out by our teams was completed at the end of 2025, and SADE is now taking over.
