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Bane NOR’s Drammen–Kobbervikdalen project aims to increase rail capacity between Drammen and Tønsberg, enabling two trains per hour to run in each direction between Oslo and Tønsberg upon its completion. The most technically challenging part of the 10 kilometers of new double-track railway is the UKD2 – Soil Tunnel, a 300-m-long tunnel section of the 7-km-long tunnel from Drammen to Kobbervikdalen.

The design of the Soil Tunnel had to overcome a number of technical challenges – primarily due to the geological/hydrogeological environment and its urban location. The tunnel had to be excavated in glaciofluvial sediments with low cohesion and high permeability below the groundwater table. Extensive jet grouting was carried out from the surface in advance of the tunneling works in order to strengthen the perimeter of the excavation profile; thus increasing stability during excavation, reducing ground movement and minimizing water ingress into the tunnel without lowering the groundwater table. In addition, strategically positioned jet grout columns helped to improve face stability and divide the jet grout ring around the tunnel into compartments that could then be dewatered prior to tunnel excavation, providing a safe and controlled environment during construction.

The comprehensive approach to the design of this tunnel also includes a tunnel waterproofing system and permanent support, as well as detailed management plans for surface and in-tunnel monitoring.

The design has been developed using Building Information Modeling (BIM), which has helped to integrate the different design packages and engineering disciplines involved into a single project coordination model. The use of 3D modeling showcases the precise engineering of critical elements such as rock injection arrays, spiles and rock bolts.