Technology Spot – Cofferdams

Cofferdams are temporary structures designed to allow the enclosed area to be pumped dry.  They are often used around bridge piers and other support structures built in water.

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Cofferdams create a dry area for working below the water level

Cofferdams can be built in a number of ways. Typically they will either be rectangular or circular. Circular cofferdams have more integral strength but require more accurate construction. Rectangular cofferdams are simpler to build but require more internal bracing to prevent the dam from collapsing in on itself due to the force of water outside its walls.

A cofferdam is typically constructed with steel sheet piles. A template is built and used to install the sheet piling in the correct place and location.

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Cofferdams are often constructed using steel sheet piles

Single skin sheet pile cofferdams are used in depths of up to 12 meters of water. For deeper depths, a secondary ring is also constructed. These double-walled sheet pile cofferdams are then backfilled with rock, sand or gravel.

Cofferdam floors may be sealed with concrete or left open, it depends upon the purpose of the dams construction.

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Cofferdams are kept dry by pumping water out of them

Commercial and Specialised Diving assist in sealing cofferdams to keep them watertight. Divers can find the leaks in between the clutches of the sheet piling and seal them from the outside. When the cofferdam is no longer required it is then removed by divers using underwater burning equipment to cut through the sheet piles.

Commercial and Specialised Diving are involved in all aspects of commercial diving construction work. We are happy to discuss any work where you may require experienced divers.  Our friendly team can be contacted on 01202 580007.