Lessons Learned in the Past Ten Years Regarding the Performance of RCC Used for Overtopping Protection and Spillways

摘要

The use of Roller-Compacted Concrete (RCC) placed on the downstream slope of embankment dams to provide erosion resistance during overtopping was started 30 years ago. Since that time, about 120 such projects have been completed in the United States to increase spillway capacity for infrequent overtopping flows. Because most of these improvements were designed to accommodate rare flooding events, little information is available on the performance of such spillways when overtopped. However, recent extreme rainfall events caused several RCC spillways to be activated. Also, there have been some spillways designed for fairly routine storm events that have been subjected to full scale testing. This paper will focus on the lessons learned and/or re-learned in the past ten years regarding the performance of RCC overtopping protection and spillways when subjected to flows from extreme flooding events, including flows carrying large amounts of gravel and rock. In addition, the paper will evaluate the performance of several RCC mixtures due to weathering effects-mainly freeze-thaw (F/T) cycles in variable climates around the country. Some of the new topics covered include: 1. The performance of two dams with RCC overtopping protection that were subjected to the 2013 flooding in Colorado. 2. The performance of an RCC faced inlet structure in Las Vegas that was subjected to an extreme rainfall event on August 25, 2013. The six hour storm event was nearly twice the annual average rainfall in Las Vegas and the resulting flows included large amounts of erosive debris. 3. The effect of aggregate gradation on the compressive strength of the RCC and the associated durability of the exposed RCC. 4. Various covers for RCC to limit F/T damage and a discussion on the use of air-entrained RCC. Based on these and other case studies, Conclusions and Recommendations are presented to improve the state of the practice for RCC overtopping protection and spillway design.