cofferdam

cofferdam temporary barrier for excluding water from an area that is normally submerged. Made commonly of wood, steel, or concrete sheet piling (see pile ), 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 caisson is preferred to the cofferdam.

Bibliography: See L. White and E. A. Prentis, Cofferdams (2d ed. 1956).

cofferdam.
1. A temporary structure in the form of an enclosed dam which can be erected on the seabed or the bed of a river and pumped dry to enable men to work within it below water level without having to wear diving suits. They are used largely in harbour works and for the construction of the piers of bridges. See also caisson.

2. Heavy transverse bulkheads in large merchant vessels, particularly tankers, built as a safety measure between the holds or oil tanks. They consist of a double bulkhead with a narrow space between them, the space frequently being used for the carriage of oil fuel or water ballast.