Immersed tube
An immersed tunnel is at the base of running water tunnel, where the tunnel consists of individual tube elements that made ashore will be sunk to their target position and then connected.
The tunnel elements that can be over 100 feet long, are usually made of concrete and steel and are manufactured in a dry dock. The open ends are welded watertight steel bulkheads. The dock is flooded and dragged the item to its destination. Here it is hung on a special ship that acts as a portal crane. By located in the tunnel element ballast tanks are slowly filled with water, the component is lowered controlled. Here, the floating crane is mainly used for securing and holding the position. Limit the part precisely to the adjacent tube piece, it is first welded from the outside or otherwise sealed before inside the hatch is opened.
In order to protect the tunnel, it is usually laid at Absenktunneln in a previously excavated trench at the bottom of the water, which is later filled.