Outside Oslo is national highway 23 (RV23), which is part of the Oslofjord link to the south of the capital. The improvement of the RV23 Dagslett - Linnes section is a consequence of the need to upgrade the original road that linked Dagslett in the municipality of Røyen and Linnes in the municipality of Lie, and forms a new national road between the E6 and E18.
The assignment includes planning 5.5 km of four-lane motorway and 2.2 km of tunnels, in addition to designing bridges, flood protection, cycle paths and footpaths, restoration of agricultural land, noise reduction and a new overpass. COWI also did the landscape design for this large infrastructure project.
This project also posed complex challenges, both geotechnical and political. Parts of the route passed through Norway’s most fertile land, with significant food production.
The solution was a buried eco-tunnel, which also reduced noise in the immediate area.
Parts of the project area also had high artesian water pressure and a lot of quicksand in the lower layers of soil. Pressure, or the effects of large volumes of water, carried a high risk of uplift when the eco-tunnel was dug.
A construction plan and working drawings were produced, including plan, cross-section and detailed drawings of noise barriers, roads, tunnels, erosion protection, bridges, cycle paths and footpaths, planting and restoration of agricultural land.
The project ensured good coordination between the disciplines with extensive use of BIM and 3D modelling.