In addition to an optimised design and technical and logistical challenges, particularly due to the compact size of the site, the presence of networks and sensitive structures also needed to be taken into account.
For the construction of a watertight retaining structure, Soletanche Bachy Fondations Spéciales used the Starsol® process, which allowed the earthworks and the excavation from the water table.
Digging by the tunnel-boring machine required meticulous analysis and organisation. Having successfully bored through the secant-pile and fibre-glass wall, the microtunnel machine and the pipeline push ahead under the thrust applied by the thrust frame installed in the working shaft. The force passes through the pipe sections that have been laid as the microtunnel machine moves forward. To limit friction, a lubricating mud is injected into the annular space of the borehole via nozzles placed at the rear of the microtunnel machine and via the jacking pipes.
Finally, logistics was a real day-to-day challenge, in order to ensure the continuous production of the microtunnel machine. Pipe deliveries and rubble evacuation trucks moving in and out of the site have been precisely measured, given the limited storage space available on the surface and the imposed truck rotation route on the CTR site.