A flagship worksite featuring an original technique developed by the experts of SADE Special Works.
Currently, SADE Special Works is handling the earthworks for this 24.25m x 7.45m, 43m-deep rectangular shaft.
Positioned in Paris on Avenue Friedland, which stretches from Boulevard Haussmann all the way to the Arc de Triomphe, the “Friedland shaft” will provide ventilation and emergency access for the future RER E regional express train station by 2022.
It is nestled in a dense urban environment, surrounded by sensitive sites: RER Line A, which runs 4.85m from its walls and the many Haussmannian buildings lining the avenue. So compacting caused by the works must be limited as much as possible to avoid any disruption.
Earthworks using a tunnel boring machine
For these reasons, when it submitted its bid, STS proposed using a tunnel boring machine for the shaft’s earthworks. This technique consists of creating the civil engineering slabs (levels, stairs, walls, etc.) in advance of the earthworks rather than at the end, as is traditionally done.
With this technique:
- less noise pollution for locals because noise is attenuated by the different slabs forming the levels of the shaft;
- the schedule is streamlined by eliminating the traditional strut setup/removal stages;
- reduced wall movement and, as a result, lower surface compacting risks.
BUT… two kinds of constraints:
- the need to avoid using temporary hoppers on the different paving levels to be able to continue the earthworks downwards;
- slightly reduced earthworks speeds.
One specific point: 2 layers of struts
The proximity of RER Line A requires the setup of 2 layers of struts, including one equipped with a cylinder system to apply a prestress force (573 tonnes x 2), further limiting movement.
For this complex setup, 8-tonne components are handled at a depth of more than 30m with only 1.90m of overhead clearance above the parts.
The earthworks will be finished in January 2021 and the carassing in June 2021.