Sefi-Intrafor’s teams have been hard at work since July to build the diaphragm walls to form the foundations of the future Stade de France station (line 15 East). There are two thicknesses of panels (1,200mm and 1,500mm), at points reaching down to a depth of more than 60m to guarantee 3m of anchorage in the Lutetian limestone. Preliminary grouting was carried out to eliminate any risk of loss of circulation and landslides when building the diaphragm walls.
Though Sefi-Intrafor’s teams have already proved their know-how on previous exceptional Grand Paris projects, it is the technique used on this project that sets it apart.
Though the 1,200mm-thick diaphragm walls have been set up “conventionally”, it’s a different story for the 1,500mm walls being built along the existing “Gare La Plaine Stade de France” high-speed regional train line B station.
The proximity of the mainline train station and the IG 90033 (previously IN0033) standard required a 3m panel opening limit along the future station’s long Northern section. The team adjusted its technique accordingly and met the customer’s demands on time despite this new requirement. Of course, the schedule to be met was even tighter, too, as the trainline operator introduced a temporary train speed limit (TSL) from 31 July to 8 January.
As a result, a modified version of the “overlap” technique was used in the TSL zone. Using this technique, both opening limit requirements can be met, and the height of the joint sealing solutions used limited. Though similar to the “overlap” technique, the term “combined seals” would be more appropriate. The panels are waterproofed using a CWS joint down to a depth of 18 metres, and from then on using an overlap joint. This joint is created by “nibbling” approx. 27cm into the primary panels. As a result, this technique requires primary/secondary panelling.
Deadline pressure meant using CWS joint sealing solutions along the covering horizons was the obvious choice to limit the cutter’s excavation surface. At the same time, a method also had to be found to brace the sheet piles, allowing the excavator to pass during the setup of the secondary panels. As soon as work began, the teams on site (assisted by the methods department) really proved their creative worth by designing reusable bracing blocks.
These blocks, a little like disused joint pipes, are removed shortly after concreting to create the space required for the excavator to pass. Using these blocks takes less time than setting up bracing solutions like Nidaplast®.
Following drilling issues, a 3rd shift was required to meet deadline requirements, particularly the TSL.
The coming year will bring further challenges as these works will continue with the setup of load-bearing elements, integral piers, and a grouted base.
The figures on this worksite are highly impressive: 16,700m² of drilling (walls), 22,000m3 of concrete, and 1,900t of reinforcements.
Client: Société du Grand Paris
Prime contractor: Egis-Tractobel
Contractor (civil engineering): Eiffage GC