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A caisson is a word that is borrowed from French caisson, which means a large box. It is related to geotechnical engineering. It is a watertight retaining structure used, for example, to work on the foundations of the bridge pier, for the construction of concrete dams or the repair of ships. It is a relatively sizeable deep foundation and is a permanent structure and part of the substructure.

Types of Caisson ;

There are four main types of the caisson, they are;

• Box caisson: Box caisson is a prefabricated concrete box that is set down on prepared basses. It is a robust watertight vessel open at the top and closed at the bottom and made of timber, steel, or RCC. Box caisson is built on land, cured, and then float or launched to the pier site where it is placed in position. Mainly it is used for shallow depth and lightweight.
• Open caisson: It is similar to box caisson, except that it does not have a bottom face and consists of vertical walls. Open caisson is suitable for soft clays, but cannot be used where there are large obstructions in the ground.
• Monolithic caisson: This caisson is more extensive than other types of the caisson but similar to open caissons. These types of caisson are often found in quay walls, where resistance to impact from ships is required.
• Pneumatic caisson: These caissons are sometimes called pressurized caissons, which penetrate soft mud. These are closed at the top and open (during construction) at the bottom. The water is excluded from the caisson chamber using compressed air.

Materials used for Caissons;

• RCC
• STEEL
• TIMBER
• CAST IRON

USES :

• It transfers the load of the structure to the hard strata.
• They are also used to install hydraulic elevators where a single-stage ram is installed below the ground level.
• It is used to provide access to a deep shaft or tunnel.
• They are used as a waterproof core wall of the earth dam.