Performance Review of RCC Spillways and Overtopping Protection

Roller-compacted concrete (RCC) has become a popular method for providing spillway and overtopping protection for earthen dams. Over the past 27-years, RCC has been used as a spillway or overtopping protection for more than 130 dams. In addition to providing protection from erosive forces of flowing water, several of these projects are located in areas exposed to numerous freeze-thaw cycles. RCC spillways and overtopping protection projects can serve as principal spillways, or in many cases, for less than the 500-year flood event. However, most RCC overtopping protection structures are emergency spillways designed to operate at a frequency not exceeding the 100-year storm. There are several reasons for the popularity of RCC with designers and owners including simplicity, speed of construction, strength and durability, and economic advantages over alternative methods. Because RCC emergency spillway and overtopping protection projects are designed to operate infrequently during major flood events, limited information is available on the actual performance of these types of structures. However, the few that have operated performed satisfactorily with no evidence of excessive wear or structural distress. Several research projects 1,2,3,4 have confirmed the excellent abrasion resistance and durability of RCC. Comparative tests on soil-cement, RCC and conventional concrete showed RCC to have a greater abrasion resistance than conventional concrete of higher strength. This was primarily due to the presence of a larger percentage of aggregate in the RCC mixture and less paste. In underwater abrasion tests using ASTM C1138, it was determined that abrasion resistance was a function of both the aggregate hardness and the strength of the paste.5 Despite the research findings, there is still the need to evaluate the reliability and performance of RCC under actual field conditions when subjected to debris laden flows and hydraulic forces. Examples of projects that have experienced multiple flows during their service lives: Ocoee, TN; Brownwood Country Club, TX; Kerrville, TX; Lower Lake Royer, MD; Lake Tholocco Dam, AL; Red Rock Detention Basin Inlet Spillway, NV. (Full paper, references) 17 pp., 9 references.