This work is conducted in strict phases, with each trade working successively on narrow worksites surrounded by active road and rail infrastructure. Meticulous phasing and the vigilance of all worksite participants are therefore essential to operate safety in this complex environment and so ensure that the project moves forward.
Concerning Soletanche Bachy’s activities more specifically, a diaphragm wall workshop was set up between June and October 2021, which excavated approximately 4,600 sq. m of walls (20% of the total). An excavation 500mm wide and to a depth of around 12m was carried out in compact sandy-gravel alluvium, using a KS hydraulic grab workshop.
Despite difficult drilling conditions (compact gravel and significant loss of fluid), concreting was carried out at a rate of approximately one pouring per day.
This was followed by a small-diameter drilling workshop from the start of August, with the installation of passive anchors (“bar” anchors, installed and sealed at 14m, sheltered from the Hi’Drill drilling operations), constituting the wall’s support level in the open-trench section of the project. The drilling work also included the construction of a 1.5m-thick grout raft in the very permeable gravel of the Drac. The grouting of bentonite-cement grout was carried out through sleeved tubes, using a container with eight computer-controlled grouting presses.
The SBFS teams meanwhile built four secant piles walls, supporting two new decks to widen the national-road bridge. The operation was repeated in December for the second half of the bridge, after moving traffic across to the completed half of the structure.
Although special works activity decreased in the autumn, while the route of the road project was adjusted, work has now resumed at a faster pace: two KS workshops have just been re-established to tackle the area of the cut-and-cover, representing the bulk of the volume of work (15,000 sq. m). Grout raft works will then be carried out, immediately followed by the earthworks and cover slabs.