Use of geocomposite drain against rapid-drawdown loading for roller-compacted concrete (RCC) armored earth dam

This case study describes the design and construction of a drainage system consisting of a geocomposite drain immediately beneath the roller-compacted concrete (RCC) slope facing at the Loxahatchee Reservoir in western Palm Beach County, Florida. 1.5 kilometers of RCC and geocomposite drain were installed along the western alignment of Cell 6. The main stability issue for the RCC was the development of excessive pore water pressure beneath the RCC in the event of rapid drawdown of the reservoir. Transient seepage analysis showed that installation of the geocomposite drain eliminated excess pore pressure beneath the RCC and dramatically increased the factor of safety against uplift, preventing structural instability of the RCC. Under the operational reservoir levels since placing the reservoir in operation, no structural instability has been observed in the RCC, which was also confirmed by post-construction transient seepage analysis. Performance of the geocomposite drain has successfully met the design objectives.