References
A86 - Carrousel shaft
FRANCE, 2005-2006
Circular diaphragm wall for a deep shaft.
As part of the Socatop project, Solétanche Bachy constructed the Carrousel shaft in 2006. The structure acts as a ventilation and emergency access shaft for the A86 which was constructed as a bored tunnel at a depth of up to 80m between Jouy-en-Josas and Rueil-Malmaison.
A special feature of this 7.80 m internal diameter shaft was its construction using diaphragm walls down to depths of 65 m. It is at this depth that the wall is anchored into water-tight strata. The excavation works was then carried thereafter out using traditional shaft sinking methods with rib supports and timbers down to a depth of 85 m. The D. Wall was then completely exposed and underpinned.
The Enpafraise system, developed by Solétanche Bachy, which allows the operator to view the precise position of the excavation tool in real time, allowed total control over vertical alignment constraints (tolerance set at 0.3%). Good vertical alignment guarantees the effectivemets of the arch effect, water tightness and the finished geometry needed for the shaft function as designed.
Techniques
A diaphragm wall is a reinforced concrete wall that is made in situ. The trench is prevented from collapsing during excavation, reinforcing and casting by the use of supporting bentonite slurry. The slurry forms a thick deposit (the cake) on the walls of the trench which balances the inward hydraulic forces and prevents water flow into the trench. A slurry made of polymers can also be used.
Ouvrages
Soletanche Bachy has developed a number of techniques for use in road structures; cut and cover tunnels, viaduct etc.
Circular shafts excavated inside a pre-formed cylindrical diaphragm wall only began to develop in a major way when modern plant became capable of digging almost perfectly vertical walls such that the cylinder can be considered self-stable without having to be tied back with ground anchors, or strengthened with struts or reinforced concrete rings.
Voyage au coeur de l'ingénierie de pointe
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