- Project Owner: Ville de Genève – Service du Génie civil
- Mission: Maîtrise d’œuvre
- Cost of the works : 4’500– kCHF
- Cost of the mission : 250’000,–kCHF
- Mission date : 2013-2015
BRIEF DESCRIPTION AND CHARACTERISTICS OF THE PROJECT
The project involves building the final section of the large-capacity (Ø150 cm) intercommunal transport tunnel, which will collect rainwater from the Florissant-La Garance catchment area, in the Malagnou district: Rue Le Corbusier – Chemin de la Boisserette – Chemin de la Chevillarde section.
Given the considerable depth of the collector (between 4 and 9 metres) and the presence of poor-quality soil below the surface water table (loam and clay that is poorly consolidated or even free-flowing), the project study led to the adoption of a trenchless excavation method, using a microtunnelling machine with the containment head held in place by bentonite pressure.
This technique is the most suitable solution from a technical and economic point of view, allowing in particular a significant reduction in the impact of the work on the surface (site noise, volume of earthworks, felling of trees, hindrance to road traffic).
The main constraints of the project were as follows:
- Work to be carried out in a public and private urban environment, where the impact of the site at all levels had to be limited.
- Construction of the firing and reception cells for the microtunnelling machine, the drop shafts, and the installation of site facilities, mostly on restricted areas with landscaping and equipment to be protected or restored after the works.
- Deformable ground beneath the water table, with existing buildings nearby, and small deviation tolerances for the height of the route.
- Demolition work
- Sheet piling (1100m2)
- Jetting columns Ø800 ground improvement (1800ml)
- Hydraulic jacking of the Ø1500 collector using a microtunnelling machine: 250ml (first shot); 165ml (second shot in a curve, radius of curvature 1500m).
- Ø1400 collector in open trench 4-6m deep (20m)
- Reinforced concrete chambers, 8m deep: concrete (400m3) Reinforcement (56T)
- 2 Ø250 private connections by directional drilling (20m)
- Roadway repairs
As a civil and geotechnical engineer, GEOS carried out a project management mission including the following services:
- Invitation to tender,
- Execution project,
- Works management. Supervision of works,
- Commissioning and completion.