In the Beginning… There is the Earth
Description of project:
The construction project aims at building a 9-storey underground car-park in the space available between several road tunnels and an existing car-park. Four apartment blocks will be built above this car-park.
The excavations carried out also include two communicating tunnels. The first occupies three car-park levels and makes the connection between two underground car-parks. The second will allow pedestrian access from the car-parks to the Fontvieille shopping centre.
In view of the proximity of the neighbouring constructions, all of the tunnel and excavation retaining works have been subject to very strict limitations on movement (10 mm).
In order to limit deformations as much as possible, the two tunnels have been built under the protection of an umbrella-arch and centering in the zones where the soils have only mediocre strength. One section of the pedestrian tunnel has been dug using explosives with radial-bolted support.
The works have been carried out using the observational method, making it possible to optimize or reinforce the retaining structures in the event of divergences between theory and reality.
For the majority of the earthworks, the bedrock is formed from Cretaceous limestone/marl. The underlying Jurassic limestone was intercepted at the level of the pedestrian tunnel connecting the car-park to the shopping centre.
Between the Cretaceous marl-limestone and the Jurassic limestone, a jumbled contact zone has been identified.
Mission entrusted to FONDASOL:
G3 execution geotechnical study and supervision mission, on behalf of the SATRI / ENGECO Contractors Group, relating to the execution studies and to the supervision of the works for the retaining walls, the excavations (micro Berlin walls with tiebacks), retaining structures, and linings of the two tunnels. Supervising the works kept an engineer fully occupied for nearly a year.
Date mission carried out: Sept. 2009 to Dec. 2011
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