Client / Owner
Territorial management department, Canton of Neuchâtel, Switzerland.
2002 - 2014
Part of a consortium, BG is responsible for the tunnel, excavation, cut-fill management, road alignment and fire protection.
2 x 2 lane highway, comprising:
- Tunnel with shallow overburden, length 800 m (double circular tube)
- Two cut-and-cover trenches, length 160 m and 150 m (rectangular sections)
- Junction to existing highway, with a half-junction, a roundabout and retaining walls.
Besides the highway section, the main road and tram line are to be realigned, an overpass constructed over the tram line, a bridge demolished; a channelled river is diverted, buildings demolished; a fill management zone is temporarily created on the lake, before converting it to a partially immersed zone returned to nature.
The highway alignment through the urban environment was optimised to account for constraints due to existing buildings and the tram line.
The section dives into the rock mass under the Serrières district. The structure is mainly excavated within the bedrock (high quality limestone). The portals are situated in zones of lacustrine deposits and other unconsolidated deposits.
The principal project constraints are:
- Structures partially beneath the level of the lake;
- Undrained tunnel, which must resist hydrostatic pressure from fissures and the lake, which implies compartmentalised double peripheral waterproofing
- Work in urban environment, shallow overburden (lack of space for site installations, additional precautions for existing structures)
- Tunnel and trenches constructed simultaneously (complex site phasing and access)
- Tunnel boring through karstified zones
- Maintained traffic flow on the road during site work (45000 vehicles per day, public transport and foot traffic) requiring multiple temporary diversions.
- Detailed design
- Production of tender documents
- Final design
- Site supervision
- As-built drawings