what is a cofferdam
Lesson 4: Cofferdams. Overview. 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.