Soletanche Bachy subsidiary Bessac has completed work on a tunnel built entirely with ultra-low carbon concrete pipes for a wastewater treatment plant in Paris, France.
The 921m linear discharge tunnel connects the new Bonneuil-en-France wastewater treatment plant to the Garges-Épinay sewer in Dugny in the north of Paris.
A consortium of Bessec, Soletanche Bachy Fondations Speciales and Setec Hydratec was appointed by the Le Croult and Le Petit Rosne valleys (Val d'Oise) intermunicipal association for water management (SIAH) to deliver the €7.8M (£6.6M) project.
The work includes the construction of 921m of 1.6m reinforced concrete pipes in one single drive with a micro tunnel boring machine (TBM).
Bessec has built the entire tunnel with 304 jacking ultra-low carbon concrete pipes – a world first.
The concrete formula has a quarter of the carbon footprint of the concretes generally used for the prefabrication of jacking pipes.
The low concrete solution was enabled by the project’s design build contract, which encouraged Bessec to use locally available materials. It was also enabled by Soletanche Bachy’s integrated materials laboratory which developed the specific concrete formulation.
Bessec’s pipes were prefabricated close to the site at a factory near Reims. This made it possible to reduce pipe transport distances and the associated carbon footprint.
For the construction of a watertight retaining structure, Soletanche Bachy Fondations Speciales used a specialised drilled piling method. The Starsol technique controls concrete placement by means of a tube that is deployed as the auger is raised.
To dig the actual tunnel structure, the team used a micro TBM. After it bored through the secant-pile and fibre-glass wall, the micro TBM pushed ahead under the thrust applied by the thrust frame installed in the working shaft.
To limit the friction on the micro TBM as it moved forward, a lubricating mud was injected into the annular space of the borehole via nozzles placed at the rear of the micro TBM and via the jacking pipes.
In May this year, the micro TBM bored through the wall of the exit shaft nearly three months ahead of the project’s contractual schedule.
The consortium will soon dismantle the tunnel equipment and remove the jacking installation so that the project’s civil engineering works can be finalised.
This project is part of Soletanche Bachy and Vinci Construction’s environmental commitment to reducing the carbon footprint of its worksites by 20% by 2030.
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