Definition - What does Cofferdam mean?
A cofferdam is a watertight, temporary, dam-like structure that is installed to enclose an area that is submerged under water to create dry conditions for workers to carry out their work. Cofferdams are built to enable construction in large water bodies like bridge piers, rigs and oil platforms by diverting the flow of water and pumping out water from the enclosed cofferdam. Also known as caissons, these temporary structures are used in trenchless technology where deep installations are involved or the soil is water bearing.
Trenchlesspedia explains Cofferdam
A cofferdam is installed to create safe working conditions for the construction of large scale water projects like dams, rigs and oil platforms. The stream of water is diverted by the cofferdam and a large enough area is enclosed. The cofferdam needs to be installed properly, and correctly pressurized to prevent failure. In cases where the cofferdams need to be taken to great depths like for piers that need to be embedded in hard strata, bottomless caissons with strong roofs are sunk. From the top of the caisson, plate iron walls are erected with an open top. In this upper caisson, the structure is built on top of the lower caisson roof until it sinks to the required depth. The workers then leave and the structure is filled with concrete.