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What is a Cofferdam?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

A cofferdam is a type of watertight construction designed to facilitate construction projects in areas that are normally submerged, such as bridges and piers. One is installed in the work area and water is pumped out to expose the bed of the body of water so that workers can construct structural supports, enact repairs, or perform other types of work in a dry environment. In some regions of the world, this construction is better known as a caisson. Working inside a cofferdam can be hazardous if it is installed improperly or not safely pressurized, but advances in engineering have led to increased safety for workers using this unique work environment.

A variety of materials can be used to construct a cofferdam, which is truly a feat of engineering. Although it is a temporary structure, it must reliably hold water back from the work area and also withstand very high pressures in order to be safe, and the construction is often used as a project for engineers learning their craft. The most basic type uses sheet metal, which is pounded into the bed of the body of water to create a watertight wall. Next, pumps are used to pull water out of the enclosure so that it will be dry. Some are built from wood or concrete, while others use a double walled mechanism, with filler made from aggregate materials in between the two walls.

A cofferdam is used to facilitate construction projects in areas that are normally submerged, such as bridges.
A cofferdam is used to facilitate construction projects in areas that are normally submerged, such as bridges.

The walls of a cofferdam can extend all the way to the surface of the water, leaving it open at the top, or it can be built as an enclosed structure. In very deep water, enclosed and pressurized ones are used for worker safety, while in shallower bodies of water, an open structure can be used. Workers access a closed cofferdam through hatches and tubes, and care is taken to make sure that the air supply is consistent and the pressure is kept at a normal level.

Sheet metal might be used to make a cofferdam.
Sheet metal might be used to make a cofferdam.

Shipwrights and repair yards also use a portable version, which can be attached to the side of a ship to enact repairs below the waterline. At sea, this can be a useful way to quickly address potential problems until the ship is taken into dry dock for more long-term repair. Minor repairs can also be undertaken with a portable one in a shipyard to avoid the expense of hauling the ship into dry dock for the work to be completed.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a InfoBloom researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a InfoBloom researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

Discussion Comments

bill55

We had great success using a temporary cofferdam supplied by Dam-it Dams.

Dipan

I would like to know that what kind of care we have to take after establishing cofferdams/or I would like to know which will be the best provision for disposal of water?

anon991

what type of Cofferdam used on the construction of the 3GORGES DAM IN China? what is the recent problems they encountered during the construction?

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    • A cofferdam is used to facilitate construction projects in areas that are normally submerged, such as bridges.
      By: jarek2313
      A cofferdam is used to facilitate construction projects in areas that are normally submerged, such as bridges.
    • Sheet metal might be used to make a cofferdam.
      By: Kybele
      Sheet metal might be used to make a cofferdam.