There has never been a submerged tunnel laid on the sea bed in Norway. The tunnel is made up of concrete modules, and will carry three lanes in each direction, separated by a central wall.
Skanska is the main contractor, and has long and extensive experience in concrete construction, but even for them this is something of an innovation. They have therefore involved BAM Civiel BV-BAM and Volker Stevin Construction Europe, who have a great deal of experience in the construction of similar tunnels. The first submerged tunnel in Scandinavia was constructed in Gothenburg in 1964, and the latest was laid as part of the Øresund link.
The six concrete modules were built at Hanøytangen near Bergen and towed around the coast separately over a duration of 5-7 days. Each concrete module is 112 m long, 10 m high, and 30 m wide, and each individual tunnel element weighs 37,000 tonnes. The first two were towed from Hanøytangen to Oslo in 2006. The next two followed in 2007, and the last two arrived at the beginning of June 2008. Sinking operations started in August and was finished November 2008.
The insurance package supplied by If includes transport insurance covering coastal towing, storage of the elements in Oslo Harbour, daily fees, and responsibility for any damage caused by the concrete elements under tow. Transport insurance starts as soon as the tug has attached the towline to the element at Hanøytangen, and ends when the vessel supervising sinking into the trench has taken over the element ready for sinking.
Insurance during storage is covered by ordinary liability insurance.
Towing large, heavy concrete modules represented a major risk, since the wind could rise, the towline could break, and the element could collide with oil installations, passing vessels, or land.
The following were taken into account during drawing up the transport insurance:
- Weather conditions, time of year, transport route, storage conditions, towing company, etc.
- Legal circumstances where under maritime law the element is not regarded as a ship, as well as the division of responsibility between the towboat and the owner of the elements.
- Additional inspections carried out at Hanøytangen by If underwriters and Skanska.
- Emergency harbours were identified; there were six between Bergen and Oslo.
- Inspection at Bjørvika covering storage risks, as well as an on-site meeting covering transport from the storage site to the construction site.
- Transport insurance covered physical damage and loss of concrete elements during transport.
- Any salvaging would have to be covered by Marine Liability
- Warranty surveyor, Bureau Vogtschmidt, Alkmaar, Holland with experience of similar towing operations, was appointed at If’s request.
Insurance conditions for transport - all risks - was used with necessary adaptations, including responsibility for the tow and condition of the insured elements at the beginning of the voyage.
Steinar Tangen/Lill M Stebbing