In July 2019, Société des Autoroutes du Nord et de l'Est de la France (Sanef) awarded Eiffage Génie Civil the contract to install the external prestressing cables on the Echinghen viaduct, one of the three viaducts in Le Boulonnais on the A16 motorway near Boulogne-sur-Mer.
This project was successfully completed thanks to the mobilization of a dozen or so employees who worked for 3 months on 11 cables between 35 and 125 meters long, with the following program in mind:
- the design of a specific prestressing anchor to adapt to the existing anchors in the structure
- installation of ducts through reinforced concrete diverters
- the transport of complete bundles of 15 lubricated sheathed strands* (TGG) through the structure
- the simultaneous towing of 15 TGGs through the sheaths by means of a 3.2 T hydraulic drawbar, permanently connected to a load cell** for towing force control.
- injection of cement grout under pressure inside ducts
- the tensioning of the 15 TGGs one by one using single-stranded cylinders
The teams also designed and custom-built for this exceptional site a part called the multitoron towing head. This allows several lubricated sheathed strands to be pulled through a small diameter sheath.
The end of this work heralds a new start for motorists on the viaduct.
Strand*: 7-wire cable made of very hard steel used for prestressing.
Weighing scale**: tool that allows the measurement (in kg) of a tractive effort to be displayed on a digital screen.
Photos Credit: Eiffage Génie Civil