Abstract
In Norway, 23 sub sea road tunnels have been built since the Vardø tunnel was officially opened in 1983. In addition eight sub sea tunnels have been built for the oil industry as shore approaches and pipeline tunnels, and another eight for water supply and sewerage. All these tunnels are excavated entirely in bedrock by drilling and blasting (no submerged culverts), with a strong reliance on probe drilling and pre-grouting, and with drained rock support structures. The Bømlafjord tunnel is presently the longest at 7.9km. The Hitra tunnel is so far the deepest at 264m below sea level; the Eiksundet tunnel under construction will reach 287m depth. These tunnels have successfully replaced many congested ferries on the stem roads and connected island communities to the mainland. In total, this represents no less than a new era in coastal communication and development. A record breaking 24km long sub sea road tunnel below a wide open fjord exposed to hard weather is at the planning stage. The Norwegian sub sea tunnel concept has gradually been implemented in other Nordic countries. The first of these was Iceland, where a 5.8km long tunnel was built below Hvalfjördur and opened for traffic in 1998. The Hvalfjördur tunnel is located in an area prone to seismic activities and risk assessment of the seismic hazard was necessary to gain the confidence of both the financing institutions and the public. In the Faroe Islands, further south in the North Atlantic, the first sub sea road tunnel was opened for public in 2002: the Vága tunnel (4.9km). Construction commenced in 2004 for a second tunnel, the Nordoya tunnel (6.2km), which is due to open mid 2006. At present 2 more projects are under consideration. Sub sea road tunnels enable highly desired improvements of the road network reducing the number of ferry connections and vitalising local businesses. A widely scattered population of 50,000 welcomes these tunnels, which on a local scale are ‘major’ projects. The concept is now spreading further. Similar sub sea road tunnels are under elaboration on other Atlantic islands; Greenland, Orkney and Shetland, and on Åland in the Baltic sea. A sub sea tunnel connecting the island of Sareemaa to the mainland of Estonia is also being considered. This paper presents the experience gained from completed tunnel projects in Norway, Iceland and the Faroe Islands, with main focus on investigation strategy, construction methods and tunnelling guidelines.