User:Macaibaya/sandbox

An undersea tunnel is a tunnel which is partly or wholly constructed under the sea or an estuary. They are often used where building a bridge or operating a ferry link is unviable, or to provide competition or relief for existing bridges or ferry links. There are several methods used to create undersea tunnels, two of which are through an immersed tube or a submerged floating tunnel. An immersed tube is one engineering method used to build undersea tunnels. A trench is created where segments of steel tubes are positioned and immersed underwater, afterwards they are joined together and the water is flushed out. A submerged floating tunnel is an undersea tunnel that uses the law of buoyancy to remain submerged underwater. The methods of holding the tunnel in place are from the sea floor where the tunnel is supported by columns or tethers, or from the surface where the tunnel can be attached to pottons. While short tunnels are often road tunnels which may admit motorized traffic, unmotorized traffic or both, concerns with ventilation lead to the longest tunnels (such as the Channel Tunnel or the Seikan Tunnel) being electrified rail tunnels.