The VL8 will connect the V10 stormwater ogee (in Athis-Mons) to the SÉSAME pumping and purification station (in Valenton). The project has multiple objectives: to strengthen and secure the sanitation network, but also to avoid the risk of discharge into the natural environment. The project is also contributing to ensuring that the Seine is “swimmable” by the 2024 Paris Olympic Games.
The VL8 collector will have a diameter of between 2.5m and 3m and a total length of approximately 10km. It will be built using tunnel boring machines and microtunnel boring machines at a depth of between 25m and 30m.
Work package 0 includes the preparatory work for future packages (civil engineering, tunnel boring machines and equipment), as well as the various shafts (entry, exit and reversing tunnel) for the tunnel boring machines. The works are mainly located in four areas.
This work constitutes the firm phase of the operation. This is the starting point for the tunnel boring machine on the SEVESO site, in the functioning treatment plant, next to the SÉSAME station.
A lot of preparatory work is planned before the foundations, including paling, surveys, tracks, construction site facilities, platform, etc. The SÉSAME attack shaft (circular and 15m in diameter) and the reversing tunnel (7m by 35m) comprise 1m thick and 45m deep diaphragm walls. A KS hydraulic grab and a Hydrofraise® will be used.
The work will continue with a temporary grout raft, embedded in the diaphragm walls to allow control of the pumping rate during the earthworks. A water-tight enclosure formed from a slurry wall will also connect the reversing tunnel to the existing station.
A wide range of work will be carried out in this Essonne town. In particular, a track will have to be created through the fields, as well as a pier on the Seine (particularly to remove cut earthworks from the diaphragm walls).
Once these preparatory works have been completed, work will be able to begin on the two circular shafts required for the project: V10 and V15, 10m and 15m in diameter respectively. The diaphragm walls are between 0.8m and 1m thick and around 41m deep.
The works are being carried out right next to a recent residence, so the SIAAP asked for acoustic screens to be installed. For the foundations, a shaft needs to be created in diaphragm walls 8m in diameter and 45m deep.
A fall shaft is planned to connect the VL8 to an existing collector beneath the quays of the Seine, under the Villeneuve-le-Roi bridge. A water-tight enclosure is planned, formed from secant piles and/or grouting.
These quays are very cramped and road access difficult. A transportation solution via the river is therefore preferred and a pier will be necessary. This pier constitutes a sub-construction project, including the removal of wrecked vehicles from around the piers, micropiles for stabilising the quay and constraints due to the RER D railway line.
All this work is spread over 30 months, starting in September 2020.