11/11/2025
Construction of the Barbin Basin in Nantes: How is the project progressing?
Launched in May 2025, the construction of the Saint-Félix basin in Nantes brings together the Demathieu Bard / Soletanche Bachy France / OTV consortium to build an underground structure designed to secure the city’s drinking water supply. The project involves creating a 6,500 m³ storage basin right in the city center. Located near the Erdre River, this complex operation combines technical expertise, environmental innovation, and a commitment to reducing disturbances in a dense urban environment.
A sensitive site with controlled acoustic constraints
Located in a densely populated urban area, the construction site requires particular attention to noise disturbances. To limit the impact on nearby residents, an electric Hydrofraise® was selected, along with acoustic protections installed both on the equipment and around the site perimeter. This approach reflects the consortium’s commitment to combining technical performance with respect for the local living environment.
Geotechnical studies and 3D modeling
Additional boreholes were carried out to validate the geotechnical model, notably by identifying the depth of the mica-schist rockhead into which the future diaphragm wall will be anchored. Analyses revealed elevation variations of around ten meters between the north and south sides of the basin (an ellipse with a major radius of 15 m).
The Soletanche Bachy France design office produced a 3D model of the basin and its surrounding geology to estimate settlements and displacements of the diaphragm wall. Based on this data, an 80-cm-thick wall was designed, anchored 1.5 to 2 meters into sound rock.
An optimized worksite in a constrained space
Soletanche Bachy France teams began setting up the site in early June 2025. The limited space required precise spatial optimization: the slurry plant was positioned with great accuracy near a partitioned spoil pit used to sort excavated materials.
By mid-July 2025, the KS grab had started excavation, while the electric Hydrofraise®, newly connected to the power grid, began cutting into the mica-schist. In total, twenty panels will be excavated to depths ranging from 16 to 26 meters.
Upcoming phases
The diaphragm wall phase is now complete, and the micropile and secant pile phases have begun. A total of 83 reinforced type-II micropiles with a diameter of 200 mm will be drilled using the Hi-Drill® method, with anchorage lengths in sound rock ranging from 7 to 13 meters. These micropiles will work in both tension and compression to support the foundation slab loads and resist groundwater pressure.
The 61 secant piles, 820 mm in diameter and 14 meters long, will be drilled to provide earth retention during excavation and carry the loads of the future technical facilities.
Drains, piezometers, and pumping wells will also be installed within the basin’s footprint before excavation work begins.
