The work is being carried out by Salini Impregilo, Impresa Pizzarotti and SWS Engineering, which were awarded the EUR 360M contract by client Bane Nor in October 2019. The tunnels will be excavated by drill-and-blast through Romb porphyry. The Kopstad tunnel will run for 880m, the Skottås for 2.9km and the Gråmunken for 1km. Overburden is low, ranging from 25m to 1m.
The tunnels will be sealed using systematic pre-injection to secure water balance in the area and safeguard the environment. The tunnel will be stabilised with bolts, sprayed concrete set for a design life of 100 years. Water and frost protection will be achieved using a membrane covered with contact-cast vault construction.
When ready for commissioning in 2024, the Drammen–Tønsberg double track will allow two trains per hour in each direction between Oslo and Tønsberg, thus more than doubling the capacity, and providing improved and more efficient transit for passengers
