Caisson

Caisson, hollow cylindrical or square tube used as a foundation, or to provide a working space for construction projects below ground or underwater. Caissons can be up to 10 m (up to 33 ft) in diameter and are usually made of concrete or steel. Construction workers or machines excavate soil from the inside of the caisson. As soil is removed from underneath the caisson, it sinks into the ground. The bottom edge of caissons are fitted with a cutting surface to make it easier to sink the structure. Certain caissons, called pneumatic caissons, are designed so that compressed air can be pumped into the structure's interior. This ensures that workers at the bottom of the caisson receive adequate oxygen and prevents soil or water from upwelling into the caisson's interior. Some caissons are used only to provide a work space underground or underwater and are removed once the construction project is complete. Other caissons are designed to become part of the foundation; these caissons are sunk deep into the ground until they reach bedrock, then are filled with concrete (see Building Construction).

HOW TO CITE THIS ARTICLE

"Caisson," Microsoft® Encarta® Online Encyclopedia 2000