24-02-2017, 10:33 AM
A submerged floating tunnel (SFT), also called a suspended tunnel or Archimedes bridge, is a tunnel that floats in the water, supported by its buoyancy (specifically, using the hydro-static thrust or Archimedes principle). The tube is placed under water, deep enough to avoid water traffic and weather, but not so deep that high water pressure has to be treated-usually 20-50 m (60-150 ft) It's enough. Cables anchored to the Earth or pontoons on the surface prevent them from floating to the surface or submerging, respectively.
Building
The concept of submerged floating tunnels is based on well-known technology applied to floating bridges and offshore structures, but the construction is largely similar to that of submerged tunnels: One way is to build the pipe into sections in a dry dock; Then they float at the construction site and sink them into place, while sealed; And, when the sections are secured together, the seals are broken. Another possibility is to build the unsealed sections, and after welding them together, pump the water out. The ballast used is calculated so that the structure has an approximate hydro-static equilibrium (ie, the tunnel has approximately the same total density as the water), while the submerged tube tunnels are weighted more to weigh them to the seabed. This, of course, means that a submerged floating tunnel must be anchored to the ground or water surface to hold it in place (which depends on which side of the tunnel the tunnel is).
History
The first underwater tunnel was built more than four thousand years ago, but the floating tunnels are much more recent. It is true that an engineer and railway builder, S. Préault, proposed but did not construct a FTS through the Bosphorus in 1860, an elegant submarine railway viaduct with spans of about 150 m based on piers located about 20 m below the surface. Hall proposed a deeper FTS for the Bosporus in 1976, but by 1977 his proposal had become an immersed tunnel buried for environmental reasons (fish habitat). A submerged tunnel is now in its place under the Bosphorus awaiting the last of the TBM to reach it. Turning now to 1882, Edward Reed proposed a rail tunnel submerged across the Channel supported by caissons, but the Parliament in England rejected it for fear of invasion. It was patented and since then, many other patents have been released for SFT, including some in the United Kingdom, United States, Norway, Sweden and Italy. Once the first immersed tunnel had been successfully built in 1893, the road was also open to build SFT - initially at least the ones that would be supported by the dock. Since 1923 the potential of an FTS has been recognised in Norway as a way to create a practical castal highway through fjords that would otherwise be too deep even for bored tunnels to make sense; Some of the existing tunnel tunnel connections even with 10% grades are very, very long. This need for shorter and shallow tunnels for a number of fjord crossings has led to detailed investigations and field tests that still continue today. The most known crossing, assessed in some detail in Norway, is for Hogsfjord, but the FTS was abandoned for local political reasons. Private investors have looked at a number of other places. Another serious contender is the Sula-Hareld crossing. The first of a series of Strait Crossing Symposia in Norway began in 1986 (the fifth was in 2009) in which SFT has played a growing part.
Building
The concept of submerged floating tunnels is based on well-known technology applied to floating bridges and offshore structures, but the construction is largely similar to that of submerged tunnels: One way is to build the pipe into sections in a dry dock; Then they float at the construction site and sink them into place, while sealed; And, when the sections are secured together, the seals are broken. Another possibility is to build the unsealed sections, and after welding them together, pump the water out. The ballast used is calculated so that the structure has an approximate hydro-static equilibrium (ie, the tunnel has approximately the same total density as the water), while the submerged tube tunnels are weighted more to weigh them to the seabed. This, of course, means that a submerged floating tunnel must be anchored to the ground or water surface to hold it in place (which depends on which side of the tunnel the tunnel is).
History
The first underwater tunnel was built more than four thousand years ago, but the floating tunnels are much more recent. It is true that an engineer and railway builder, S. Préault, proposed but did not construct a FTS through the Bosphorus in 1860, an elegant submarine railway viaduct with spans of about 150 m based on piers located about 20 m below the surface. Hall proposed a deeper FTS for the Bosporus in 1976, but by 1977 his proposal had become an immersed tunnel buried for environmental reasons (fish habitat). A submerged tunnel is now in its place under the Bosphorus awaiting the last of the TBM to reach it. Turning now to 1882, Edward Reed proposed a rail tunnel submerged across the Channel supported by caissons, but the Parliament in England rejected it for fear of invasion. It was patented and since then, many other patents have been released for SFT, including some in the United Kingdom, United States, Norway, Sweden and Italy. Once the first immersed tunnel had been successfully built in 1893, the road was also open to build SFT - initially at least the ones that would be supported by the dock. Since 1923 the potential of an FTS has been recognised in Norway as a way to create a practical castal highway through fjords that would otherwise be too deep even for bored tunnels to make sense; Some of the existing tunnel tunnel connections even with 10% grades are very, very long. This need for shorter and shallow tunnels for a number of fjord crossings has led to detailed investigations and field tests that still continue today. The most known crossing, assessed in some detail in Norway, is for Hogsfjord, but the FTS was abandoned for local political reasons. Private investors have looked at a number of other places. Another serious contender is the Sula-Hareld crossing. The first of a series of Strait Crossing Symposia in Norway began in 1986 (the fifth was in 2009) in which SFT has played a growing part.