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Cofferdam

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Definitions

A cofferdam is a watertight and sometimes temporary structure built in place to facilitate construction projects in areas that are usually submerged such as bridges, piers, and shipyards. Also called a caisson, the cofferdam is constructed within the work area and then the water is pumped out, exposing the floor bed and leaving it to dry so construction can be carried out, structural supports put in place, and repairs if any, made.[1] The structure must be tightly and properly constructed to ensure that the water is kept out of the exposed work area. Cofferdams are built using a variety of materials such as earth, wood, concrete, and steel.[2]

Contents

[edit] Earthen

An earthen cofferdam is constructed by dumping earth fill into the water and shaped to surround the construction area. The use of earthen cofferdams are limited to sluggish, shallow waterways as the earth material can be carried away by strong tides or currents. It is also common to construct an earthen cofferdam in combination with a type of sheathing or cribbing.[3]

[edit] Wooden

A wooden cofferdam uses wooden sheathing that is primarily interlocked timber sheathing driven as a single wall and supported by stringers and cross struts. It can also be driven in double rows as a wall. The rows of wooden sheathing are then connected and tied with braces.[4]

[edit] Steel

Steel cofferdams are the most commonly used. Steel sheet piling or sheet metal that comes in various shapes, sizes, and weight is interlocked and driven in a row to form a very tight structure. It is then additionally supported by a framework of stringers and struts.[5]

[edit] Other

Cofferdams can also be built with wooden or concrete cribbing that provides added stability to the structure’s walls. Another type of cofferdam is a double-walled structure that places filler of an aggregate material in between the two walls.[6]

[edit] References

  1. What is a Cofferdam. Wisegeek. 2008-09-30.
  2. Construction. Integrated Publishing. 2008-09-30.
  3. Construction. Integrated Publishing. 2008-09-30.
  4. Construction. Integrated Publishing. 2008-09-30.
  5. Construction. Integrated Publishing. 2008-09-30.
  6. What is a Cofferdam. Wisegeek. 2008-09-30.