The Follo Line Project is a new railway line between Oslo Central Station and the public transport hub at new Ski station (20km long twin tunnels). The concrete tunnel will be connected to both existing constructions at Oslo Central station and to the long tunnel, the longest railway tunnel to date in the Nordic countries.
The Drill & Blast contract includes the construction of several tunnels built in Ekebergåsen (1.3km), a hill formed by gneiss of the Precambrian period with presence of alum shale, located east of the Oslo fjord. The tunnel (design and construction) has a lot of challenges due to the presence of existing tunnels (raw water tunnel and escape tunnels) and oil deposits (watertight section).
The Oslo S contract includes the construction of a cut and cover tunnel from 6 to 2 tubes (625m) and 4 technical buildings. The cut and cover area is characterised with severe geotechnical condition – quick clay – that required the use of ground improvement (jet grouting).