Tunnels and underground constructions
- General Contractor: City of Geneva – Civil Engineering Department
- Assignment: Project Management
- Total cost of work: 4,500k CHF
- Total cost of the assignment: 250,000k CHF
- Completion Date: 2013-2015
PROJECT DESCRIPTION AND CHARACTERISTICS
The project involves construction of the last section of the high-capacity inter-communal transport gallery (Ø150 cm), allowing for collection of rainwater from the Florissant-La Garance watershed in the district of Malagnou: section Rue Le Corbusier – Chemin de The Boisserette – Chemin de la Chevillarde.
Given the high depth of the collector (4 to 9 meters deep) and the presence of poor quality groundwater (silts and clays not consolidated or even fluent), the study of the project resulted in adoption of a trenchless excavation method and the use of a microtunnel boring machine with maintenance of the confinement head with bentonite pressure.
This technique is the most suitable solution from a technical and economic point of view, making it possible in particular to reduce significantly the impact of surface works (construction site noise, volume of earthworks, trees felling, and traffic).
The main constraints of the project were:
- Works in a public urban and private residential context, on which the impacts of the construction site at all levels are to be limited.
- Realization of the firing and reception cells of the microtunnel boring machine, of the drop wells, and the installation of site installations mainly on limited areas with landscaping and equipment to be protected or restored after work.
- Groundwater deformable sites, with existing buildings nearby, and low tolerances of deviation from the altimetry plot.
Technical characteristics
- Demolition works
- Sheet piling (1100m²)
- Jetting columns Ø800 soil improvement (1800ml)
- Hydraulic connection of the collector Ø1500 to the microtunnel boring machine: 250ml (first firing); 165ml (second shot in curve, radius of curvature 1500m).
- Collector Ø1400 in open trench 4-6m deep (20m)
- Reinforced concrete chambers, 8m deep: concrete (400m³) Armature (56T)
- 2 private connections Ø250 per directional drilling (20m)
- Pavement repairs
ASSIGNMENT
As a civil and geotechnical engineering firm, GEOS has carried out a project management mission comprising the following tasks/duties:
- Invitation to tender,
- Execution project,
- Construction management,
- Commissioning and completion.
