Caisson

Caisson is a watertight box like a structure. Which is used in the areas where the underwater works are carried out like bridge pier, break water and shore protection work, large water front structure. It is an open chamber which kept water out by air pressure. It is part of the complete structure like cofferdam it is not removed after completion of work.

A caisson wall is an excavation support system constructed by vertically drilled holes to form an interlocking secant wall.

Caissons are made of materials like timber, steel, masonry and reinforced concrete. To install a caisson in place, it is brought down through soft mud until it come across to the suitable foundation material. While bedrock is preferred, a stable, hard mud is sometimes used when bedrock is too deep.

They are strong enough to with stand horizontal as well as vertical loads.

There are different kind of caissons are available.

Ø Box Caisson: It is cured and cast on land and then sunk into a place. It has a closed bottom and open top. It is made up of timber or reinforced concrete. It is generally economical.

Ø Open Caisson: It is made up of timber, steel or concrete box and it is open from top and bottom. There are three different types of open caisson. Single wall and cylindrical. Single wall is a caisson consists of vertical walls. Cylindrical shell of this caisson is made up of timber, masonry, steel or reinforced concrete which is sunk by excavating the soil within the shell.

Ø Pneumatic caisson: This type of caisson is closed at top and open at bottom. The water is excluded from the caisson chamber by means of compressed air.

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