Many dams, especially earthen embankment dams constructed prior to 1960, do not meet today's higher hydraulic design criteria. Hydrologically deficient, these earthen dams were simply not designed to safely store or pass at least one-half the calculated probable maximum flood. As engineers search for cost-effective ways to rehabilitate deficient embankment dams, more and more of them are discovering the value of roller-compacted concrete (RCC) overlays.
RCC overlays provide earthen dams the safety and reliability of conventional-slump concrete, but at considerably less cost. Because RCC is a no-slump concrete, it can be transported by dump truck, front-end loader, scraper, or conveyor; spread by dozer; and compacted quickly by vibratory roller. Typically placed on the downstream slope of an earthen dam in 1-foot-thick horizontal lifts, RCC functions as an armor plate, creating a stable composite structure with increased spillway capacity. Thus, the embankment can be safely overtopped during a flood.
The growing popularity of these overlays is due in large part to the speed and simplicity of the RCC construction method. The RCC overlay on the embankment's downstream slope can be placed without lowering the reservoir level, and because RCC can be handled relatively easily with large volume equipment, it's possible to place more than 1,000 yards of RCC per day.