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cofferdam,temporary barrier for excluding water from an area that is normally submerged. Made commonly of wood, steel, or concrete sheet piling (see pilepile,
post of timber, steel, or concrete used to support a structure. Vertical piles, or bearing piles, the most common form, are generally needed for the foundations of bridges, docks, piers, and buildings. Slender tree trunks, roughly trimmed and about 10 in. (25.
..... Click the link for more information. ), cofferdams are used in constructing the foundations of dams, bridges, and similar subaqueous structures and for temporary drydocks. If double sheeting is utilized, the space between the sheets is usually filled with clay and gravel. When great strain or pressure is likely to be encountered, as in deep water, the pneumatic caissoncaisson
[Fr.,=big box], in engineering, a chamber, usually of steel but sometimes of wood or reinforced concrete, used in the construction of foundations or piers in or near a body of water. There are several types.
..... Click the link for more information. is preferred to the cofferdam.
See L. White and E. A. Prentis, Cofferdams (2d ed. 1956).
a narrow airtight compartment separating neighboring units on a ship. It prevents the penetration from one compartment to another of gases given off by petroleum products. Cofferdams, for example, isolate living quarters from tanks of liquid fuel. Freight tanks on tanker ships are separated by cofferdams from bow compartments and machine rooms. Cofferdams are filled with water during the transporting of cargoes with low flash points. Gases accumulating in cofferdams are removed by means of ventilation systems. Many obsolete war-ships had cofferdams, called waterproof compartments, situated along the sides of the ship not protected by armor; they protected against the penetration of water through underwater punctures.
a watertight barrier for protecting hydraulic engineering structures or work sites from flooding during construction or repair. Cofferdams are built of earth (either dry fill or alluvial deposits), rock fill, or wood; more rarely, they are built of concrete and metal.
A temporary, wall-like structure to permit dewatering an area and constructing foundations, bridge piers, dams, dry docks, and like structures in the open air. A dewatered area can be completely surrounded by a cofferdam structure or by a combination of natural earth slopes and cofferdam structure. The type of construction is dependent upon the depth, soil conditions, fluctuations in the water level, availability of materials, working conditions desired inside the cofferdam, and whether the structure is located on land or in water (see illustration). An important consideration in the design of cofferdams is the hydraulic analysis of seepage conditions, and erosion of the bottom when in streams or rivers.
Where the cofferdam structure can be built on a layer of impervious soil (which prevents the passage of water), the area within the cofferdam can be completely sealed off. Where the soils are pervious, the flow of water into the cofferdam cannot be completely stopped economically, and the water must be pumped out periodically and sometimes continuously.
A nautical application of the term cofferdam is a watertight structure used for making repairs below the waterline of a vessel. The name also is applied to void tanks which protect the buoyancy of a vessel.