Caderaux Tunnels in Nîmes: Capremib's tunnel segments contribute to the creation of a unique structure in France to protect the city from flooding

Since 1988, the city of Nîmes has been affected by violent Cévennes episodes causing dramatic flooding. As a result, the metropolitan area has implemented numerous preventative measures to protect its residents.

The latest project aimed at strengthening the existing network of underground galleries is the digging of the Uzès and Limites canal tunnels, located to the east of the city, to evacuate heavy rains through the subsoil as quickly as possible.

For the creation of these unique prevention structures in France, excavated using a tunnel boring machine, the lead company RAZEL BEC called upon the expertise of CAPREMIB, a recognized specialist in custom-made prefabricated concrete for the building and civil engineering markets, for the manufacture of the low-carbon prefabricated reinforced concrete voussoirs.

As part of the Flood Prevention Action Programme launched in 2020, aimed at increasing the hydraulic capacity of the Uzès and Limites canals tenfold, the Nîmes Metropolis wanted to increase the capacity of existing infrastructure which was no longer sufficiently sized to ensure the safety of residents living in this dense urban area, east of the city.

A first in France for this type of construction, two underground tunnels, representing a length of 2,2 kilometers and an internal diameter of 3,30 meters, were excavated at depths of 2 and 6 meters underground by a tunnel boring machine. Shaped like a Y, they are composed of two culverts: the Uzès culvert, 980 meters long, and the Limites culvert, 1220 meters long.

At the request of the lead contractor RAZEL BEC, CAPREMIB supplied high-performance precast concrete voussoirs (C60/75) that guarantee their durability. They form the rings that make up the final lining of the structure and ensure its watertightness and resistance to external pressure.

CAPREMIB manufactured two types of rings with connectors and bolts, made up of 6 voussoirs, produced from low carbon concrete incorporating CEMIII cement:

Some are 1 m long, with a 30 mm pinch and a minimum radius of curvature of 130 m to follow the curves of the project,
and others 1,20 m long, with a pinch of 30 mm and a minimum radius of curvature of 180 m.

The tunnels will have approximately 478 rings with a length of 1 meter and 1.465 with a length of 1,20 meters, i.e. 11.658 voussoirs.

The manufacturing of the tunnel segments, which began in April 2024, was completed in August 2025. Carried out in tandem with the tunnel excavation, their daily delivery was ensured by 5 to 6 trucks. This efficient logistics operation was particularly impressive considering the 850 km distance between the construction site and the Capremib manufacturing plant.

This new structure represents a key step for the Nîmes metropolitan area to significantly reduce the risk of flooding in the eastern part of the city.