A cofferdam (also called a coffer) is a temporary enclosure built within, or in pairs across, a body of water and constructed to allow the enclosed area to be pumped out, creating a dry work environment for the major work to proceed. Enclosed coffers are commonly used for construction and repair of Oil platforms, bridge piers and other support structures built within or over water. These cofferdams are usually welded steel structures, with components consisting of sheet piles, wales, and cross braces. Such structures are typically dismantled after the ultimate work is completed.
For dam construction, two cofferdams are usually built, one upstream and one downstream of the proposed dam, after an alternative diversion tunnel or channel has been provided for the river flow to bypass the dam foundation area. These cofferdams are typically a conventional embankment dam of both earth- and rock-fill, but concrete or some sheet piling also may be used. Typically, upon completion of the dam and associated structures, the downstream coffer is removed and the upstream coffer is flooded as the diversion is closed and the reservoir begins to fill. Dependent upon the geography of a dam site, in some applications, a "U"-shaped cofferdam is used in the construction one half of a dam. When complete, the cofferdam is removed and a similar one is created on the opposite side of the river for the construction of the dam's other half.
The cofferdam is also used on occasion in the shipbuilding and ship repair industry, when it is not practical to put a ship in drydock for repair or alteration. An example of such an application is certain ship lengthening operations. In some cases a ship is actually cut in two while still in the water, and a new section of ship is floated in to lengthen the ship. Torch cutting of the hull is done inside a cofferdam attached directly to the hull of the ship, and is then detached before the hull sections are floated apart. The cofferdam is later replaced while the hull sections are welded together again. As expensive as this may be to accomplish, use of a drydock may be even more expensive. See also caisson.
A 100 ton open caisson that was lowered more than a mile to the sea floor in attempts to stop the flow of oil in the Deepwater Horizon oil spill has been called a cofferdam. It did not work as methane froze in the upper levels preventing the containment.
A cofferdam may also refer to an insulating space between two watertight bulkheads or decks within a ship. A cofferdam may be a void (empty) space or a ballast space. Cofferdams are usually employed to ensure oil or other chemicals do not leak into machinery spaces. If two different cargoes that react dangerously with each other are carried on the same vessel, one or more cofferdams are usually required between the cargo spaces.
The division between the tanks and the hull of a double-hulled vessel is not normally called a cofferdam, although it serves this function.
- ^ "Coffer", The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. (accessed 16 Jan. 2008)
- ^ http://www.bp.com/genericarticle.do?categoryId=9033571&contentId=7061864
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Look at other dictionaries:
Cofferdam — Cof fer*dam, n. A water tight inclosure, as of piles packed with clay, from which the water is pumped to expose the bottom (of a river, etc.) and permit the laying of foundations, building of piers, etc. [1913 Webster] … The Collaborative International Dictionary of English
Cofferdam — Cofferdam, s. Kofferdamm … Meyers Großes Konversations-Lexikon
Cofferdam — (engl.), s.v.w. Kofferdamm … Kleines Konversations-Lexikon
cofferdam — [kɔfɛʀdam] n. m. ÉTYM. 1891 (Année sc. et industr. 1892, p. 147); de l angl. coffer « coffre », et dam « digue ». ❖ ♦ Techn. (mar.). Séparation formée par deux cloisons transversales entre un compartiment à cargaison et la chambre des machines…… … Encyclopédie Universelle
cofferdam — m DEFINICIJA v. koferdam … Hrvatski jezični portal
cofferdam — [kôf′ərdam΄, käf′ərdam΄] n. [ COFFER + DAM1] 1. a watertight temporary structure in a river, lake, etc., for keeping the water from an enclosed area that has been pumped dry so that a bridge foundation, dam, or pier may be constructed 2. a… … English World dictionary
cofferdam — /kaw feuhr dam , kof euhr /, n. 1. a watertight enclosure placed or constructed in waterlogged soil or under water and pumped dry so that construction or repairs can proceed under normal conditions. 2. Naut. a sealed void between two bulkheads,… … Universalium
Cofferdam — Un cofferdam ou maille sèche est un espace de séparation entre deux parties de la coque d un navire ; il est délimité par deux cloisons étanches de part et d autre. Les cofferdams sont utilisés sur les navires cargo pour séparer la salle des … Wikipédia en Français
cofferdam — noun Date: 1736 1. a watertight enclosure from which water is pumped to expose the bottom of a body of water and permit construction (as of a pier) 2. a watertight structure for making repairs below the waterline of a ship … New Collegiate Dictionary
cofferdam — noun a) A temporary watertight structure that is pumped dry to enclose an area underwater and allow construction work on a ship, bridge, or rig to be carried out; a caisson. b) An empty space that acts as a protective barrier between two floors… … Wiktionary