GC: n
CT: A cofferdam is a temporary structure designed to keep water and/or soil out of the excavation in which a bridge pier or other structure is built. When construction must take place below the water level, a cofferdam is built to give workers a dry work environment. Sheet piling is driven around the work site, seal concrete is placed into the bottom to prevent water from seeping in from underneath the sheet piling, and the water is pumped out. The word “cofferdam” comes from “coffer” meaning box, in other words a dam in the shape of a box.
This lesson covers structural cofferdams as temporary installation, explaining in step-by-step detail proper and safe methods and materials to be used. There are different types of cofferdam, some are used to support excavation operation and some are enclosed type box placed in the water.
S: http://courses.washington.edu/cm420/Lesson4.pdf (last access: 30 December 2014)
N: 1. the English word cofferdam derived from the English word coffer, derived from the Old French word coffre, derived from the Vulgar Latin word cophinus (basket, hamper), derived from the Greek word kophinos, κόφινος (a (small) basket), derived from the Old French word cofre, derived from the French root *cofne, derived from the Vulgar Latin word cophinus (basket, hamper), derived from the Greek word kophinos, κόφινος (a (small) basket), derived from the English word dam, derived from the Proto-Germanic root *dammaz.
2. A cofferdam is a structure that retains water and soil and allows the enclosed area to be pumped out and excavated dry. Cofferdams are commonly used for construction of bridge piers and other support structures built within water. Cofferdam walls are usually formed from sheet piles that are supported by walers, internal braces and cross braces. Cofferdams are typically dismantled after permanent works are completed. Since cofferdams are usually constructed within water, the sheet piles are installed using preconstructed templates that permit the correct positioning of each sheet pile from a barge.
3. Cofferdam types:
- Braced cofferdams: They are formed from a single wall of sheet piles that is driven into the ground to form a “box” around the excavation. The sheet piles are then braced on the inside and the interior is dewatered. It is primarily used for bridge piers in shallow water (30 – 35 ft, 9 to 12m depth).
- Cellular cofferdams: Cellular cofferdams are used only in those circumstances where the excavation size precludes the use of cross-excavation bracing. In this case, the cofferdam must be stable by virtue of its own resistance to lateral forces.
- Double-walled sheet pile cofferdams: They are cofferdams comprising two parallel rows of sheet piles driven into the ground and connected together by a system of tie rods at one or more levels. The space between the walls is generally filled with granular material such as sand, gravel or broken rock.
4. coffer dam: this term is often generalized to include watertight lining of excavations in the ground for the purpose of keeping out ground water.
5. coffer dam: term standardized by ISO.
S: 1. http://www.myetymology.com/english/cofferdam.html (last access: 30th December 2014). 2 & 3. http://www.deepexcavation.com/en/Cofferdam-cellular-cofferdams (last access: 30 December 2014). 4 & 5. TERMIUM PLUS (last access: 30 December 2014).
OV: coffer dam, coffer-dam.
S: TERMIUM PLUS (last access: 30 December 2014)
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