The contract for blasting the tunnel, worth NOK 347 million, was awarded to Scandinavian Rock Group. Construction commenced on 14 April 1997. In addition to attack from both ends, blasting was also carried out from a long crosscut on the Hurum side. A major accident took place on 9 October, when a pile of stones fell onto a worker. Most of the tunneling took place through bedrock gneiss. However, in January 1998 the tunnelers met a wall of sediments. Although projected, it turned out to be more than thick, instead of the expected , delaying the project with six weeks. The segment was overcome by injecting concrete to create a shell before removing the masses. Thus a diverting tunnel was blasted in a curve under the area to allow work to continue while work continued on the weak zone. The issue added NOK 30 million to the construction costs. The zone, created by an ancient river, was overcome by freezing the section and then blasting through it. Then a thick and long concrete shell was built to give the area structure. The tunneling was completed on 4 February 1999.