Ramboll was chosen to undertake overall repairs on the Limfjorden immersed highway tunnel, which has a total length of 550 meters. This tunnel was built in the late sixties and carries highway traffic in six lanes; of the total length, 510 meters of it are immersed precast elements made of reinforced concrete. The remaining 40 meters are in situ cast reinforced concrete structures, from the tunnel approaches to the access ramps from the highway.
As a result of leakages, cracks and delaminations, the structural concrete had become severely contaminated with chlorides over the years - this caused extensive corrosion on the reinforcements. The work was carried out between 1993 and 1998, over a number of phases.
Phase 1 included a longitudinal post-tensioning of the tunnel structure, in order to eliminate structural problems and facilitate a durable repair of the severely deteriorating areas in the tunnel. Phase 2 included the injection of cracks and construction joints to stop leakages through the tunnel walls and ceiling. Phase 3 included renovations of the tunnel walls and ceiling, by repairing concrete and corroding reinforcement as well as the installation of a new tile-cover on the tunnel walls.
In relation to the renovation activities, a fire safety analysis was performed on the tunnel structure to assess the need for fire protective cladding and the adequacy of the existing ventilation system in case of fire.