Question

Explain sheet pile cofferdams.

Answer 1

A cofferdam is a structure that retains water and soil that 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. Cofferdams walls are usually formed from sheet piles that are supported by walers and 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

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Answer 2

A cofferdam is a retaining structure, usually temporary, which is utilized to keep water or earth out of an excavation site until the permanent works are constructed. Such struc- tures usually consist of vertical sheet piling walls forming a closed perimeter and braced internally or externally by a sys- tem of structural members or ties.

The bracing system consists of horizontal members called wales, which transfer loads from the sheet piling to compres- sion members called struts, or to external supports called tie backs or anchors.

The safe design of these temporary structures is important, since the safety of workmen or the protection of other struc- tures is almost always involved. The participation of wales and struts in the overall stability of cofferdams must be eval- uated much more closely than the support system of an anchored bulkhead. The sequence of construction regarding the excavation of soil or the pumping out of water from a cof- ferdam will affect the loads on all elements of the system. Maximum loading conditions may occur during the construc- tion phase, or during the placement of permanent work due to removal or relocation of bracing, rather than after the cof- ferdam is completed. In addition, pressures outside the wall may contribute to instability of the floor of the cofferdams that must be evaluated and accounted for in design planning

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