These dam consists of two straight, parallel vertical walls of sheet piling, tied to each other and the space between walls filled with soil. The width between the parallel piles is empirically set as (h/2 + 1.5m); where h is height of water. Double-wall sheet piling coffer dams higher than 2.5m should be strutted. Sometimes, an inside berm is provided to keep the phreatic line within the berm.
The fill material should have a high coefficient of friction and unit weight so that it performs as a massive body to give the coffer dam stability against sliding and overturning. Suitable measures should be adopted to reduce the uplift on the coffer dam. This is generally done by driving the sheet piling on the upstream as deep as possible.
The double-wall sheet piling cofferdam has the advantage of having less leakage than that in a single-wall cofferdam. These coffer dams are suitable upto a height of 10m.
(This article comes from CivilEblog editor released)