Norway's breathtaking coastline is deeply indented by complex networks of fjords, creating formidable geographical obstacles for transportation. Traversing the coastal highway E39 currently requires multiple lengthy ferry journeys, as conventional civil engineering approaches fail: the fjords are often over 1,000 meters deep and over a mile wide, making bottom-supported bridge piers impossible and traditional bored seabed tunnels astronomically expensive or topographically impractical due to steep gradients. To solve this, Norwegian engineers are pioneering the Submerged Floating Tunnel (SFT), often referred to as an Archimedes bridge.
An Archimedes bridge consists of twin concrete or steel tubular structures submerged approximately 30 meters beneath the water surface—deep enough to allow massive cruise ships and naval vessels to pass safely overhead without disturbance, and far enough down to avoid surface wave turbulence and weather. The fundamental engineering relies on Archimedes' principle of buoyancy: the structure is engineered to be net buoyant, floating upward due to displaced water weight. To maintain precise stability, the tubes are anchored down to the seabed with heavy steel cables or tied to floating surface pontoons, creating tension that resists currents, seismic shifts, and water pressure dynamics.
Internal ballast systems allow fine-tuning of buoyancy forces as vehicle traffic weight fluctuates inside the concrete tubes. This groundbreaking combination of offshore oil platform tethering mechanics and marine physics offers a revolutionary blueprint for future deep-water infrastructure across the world.