Submerged Floating Tunnels: is it time?

Federico Perotti

Though a first realization is still missing, the Submerged Floating Tunnel is deemed to be a competitive option for crossing sea straits, fjords, alpine lakes and waterways in general. This is, first of all, for environmental reasons related to the small, or virtually zero, visual impact of the infrastructure and to the small occupation of surface land. Secondly, because among the various crossing solutions, the SFT should be the one less prone to interruption/limitation of its operability due to adverse weather conditions, this being of utmost importance when public transportation is involved.
On the contrary, adverse psychological reasons come from the novelty of the approach; in this light, a prototype installation was proposed some years ago within an international project. The prototype was thoroughly designed but never built, though remaining, in this writers’ opinion, a necessary step towards the installation of the first “real” SFT.
After many years in which design proposals, numerical simulations and a long-lasting debate were carried on it seems to be high time for reviewing some of the basic ideas and conceptual design options that were at the basis of the research activity performed in the late 90s and in the first decade of the new millennium, also in view of some emerging facts and situations; first of all, and on the “supply” side, the augmented capabilities of the scientific community to face complex physical experiments and numerical simulations. Secondly, by the “demand” point of view, the considerable pressure exerted by new initiatives; first of all, the Norwegian E39 coastal highway project involving the crossing of eight major fjords, today operated by ferries, and envisaging the adoption of a SFT for crossing the Bjørnafjord.
In this light some general considerations and remarks will be summarized in the seminar, also focusing on open issues related to the simulation of the behavior of SFTs under extreme environmental loads.