Drake Lake Dam — A Performance Case History

Drake Lake Dam was constructed during the summer of 2000 as part of the development of the Jim Edgar/Panther Creek State Fish and Wildlife Area in Cass County, Illinois. The earthen dam on a natural soil foundation has a length of 450 feet and a height of 45 feet with 3H:1V upstream and downstream slopes. The dam has a principal spillway structure consisting of a cast-in-place concrete drop inlet tower, a 36-inch reinforced concrete pipe (RCP) outlet pipe, and an impact-basin-type energy dissipater/outlet structure. Construction of the earthen embankment began in July 2000 and ended in September 2000. During the latter stages of construction, observed and measurable distress of the dam was detected in the inlet tower and RCP outlet pipe. The movement measured in the principal spillway intake tower and the 36-inch RCP was the result of lateral spreading and vertical cracks in the embankment dam, both in the downstream and upstream direction, due to rapid embankment filling over the soft, silty clay foundation soils. Redesign of the dam structure was required to account for these unexpected site conditions. Results of monitoring the dam during and after construction are presented