A caisson (also French Caisson ) is a box , which as a foundation is sunk or as a working space under the water surface. For underwater work, the water is displaced with overpressure in the caisson, similar to a diving bell . The process has been used for underwater work since the mid-19th century.
The caisson is usually built on land and then towed to the required location on the water and sunk. It is often necessary to lower the caisson into the ground by a certain amount. In this case it is used as a work space that is open at the bottom. In order to prevent the surrounding water from penetrating, the cavity is placed under a coordinated excess pressure.
Then the material of the ground can be removed - the caisson can then be lowered further and further. Once the required depth has been reached, the cavity is filled with concrete , usually using the contractor method. In this way, for. B. the foundation of a bridge pier.
There is a health risk for people who work in such an overpressurized sinker. If the pressure drop is too rapid when exiting the caisson, gas bubbles can form in the blood. This so-called caisson disease can lead to paralysis or death. In the meantime, this danger is counteracted by workers who, after their work in the caisson, go through a pressure lock into a decompression chamber , in which the pressure is continuously reduced over a longer period of time.
The first bridge in which caissons were used on a larger scale was Westminster Bridge (from 1739).
Structures realized with the help of caissons:
- Old Elbe Tunnel , Hamburg
- Bay Bridge , San Francisco
- Brooklyn Bridge , New York City
- Drogden tunnel , Øresund connection
- Freihafenelbbrücke , Hamburg
- La Pallice
- Rhine bridge Kehl
- Red sand
- Saalach power station Bad Reichenhall , barrier system
- Scheldt overhead line crossing Doel
- Skye Bridge , Scotland
- Spree Tunnel Friedrichshagen , Berlin
- Underground access system (UES) of the Bundestag , Berlin
- Lipno reservoir
- Strelasund overhead line crossing
- Tiergarten Tunnel , Berlin
- Tower Bridge , London
- Transbay Tube , San Francisco
- Westminster Bridge , London
In the film Wasser für Canitoga (1939), the principle of the caisson and its dangers are explained: In the finale of the film, Hans Albers gets into a life-threatening situation while working in a caisson due to excessive pressure differences.
- cf. Charles Welch: History of the Tower Bridge, Smith, Elder and Co., London 1894, pp. 187 f.