Thirty years of experience with subsea tunnels

In Norway 25 subsea road tunnels, representing a total length of more than 100km and 8 subsea tunnel projects for oil and gas pipelines, water supply and sewerage, representing a length of almost 40km, have been completed since the early 1980’s. The tunnels are located in a variety of geological conditions, varying from hard, very good quality rock to less competent rocks such as shale, schist and phyllite. The deepest part of such tunnels often coincides with weak zones or faults, representing difficult excavation conditions. This paper is focusing primarily on the experience from the Norwegian subsea road tunnels. As introduction, the characteristics and geological conditions of the tunnels are reviewed, and the main principles of investigation and design and procedures for excavation and rock support are discussed. Operation and maintenance of the Norwegian subsea road tunnels is also covered by the paper, as well as traffic and fire safety. Finally, plans for future projects in Norway, and the consequences of the new EU tunnel safety directives for existing and future subsea projects, are briefly described.