Design of the Submerged Floating Tunnel operating under various conditions

In Norway there has been identified several crossings with a variety of different conditions under which a Submerged Floating Tunnel, SFT or Archimedes Bridge, may be used. In the Høgsfjord project whose feasibility was well documented before the project was stopped for local political reasons the length was some 1400 m, the water depth about 150 m and the site was well protected from large sea waves. However, swell, vortex shedding and slowly varying internal waves due to layers of different salinity presented a hazard of significant dynamic oscillations. In the wake of the Høgsfjord project feasibility studies have been undertaken in Norway for sites at the very inlet of a fiord directly exposed to the big North Sea waves, in an inland lake with ice infested waters, in fiords threatened by large waves induced by huge, falling rock masses, and most recently the largest fiord in the country, the Sognefjorden which at the identified crossing site is 3700 m wide and 1250 m deep. In addition to the challenge of these various conditions some common accidental situations have to be solved for all applications including fire, sinking ships, falling anchors as well as sudden massive water ingress into the tube. The paper discusses the design challenges presented by the various conditions and pros and cons for alternative technical solutions for these various applications and summarizes some of the experiences learned by the Norwegian studies.