I Dare You to Knock This Off! Physical Model Testing of Crest Caps on RCC Overlays

ABSTRACT ONLY - Overtopping protection using roller-compacted concrete (RCC) overlays is a common improvement made to address hydrologic deficiencies at existing small- to medium-height embankment dams. Overlays allow floods to pass over the dam while preventing erosion of the original embankment. For one dam modified with an overlay in 1993, deterioration of the RCC and poor bonding between lifts has caused concern that overtopping flow could cause a sliding failure of the two 0.3-m (1-ft) thick lifts of RCC that cap the crest. Analytical and computational fluid dynamics (CFD) studies conducted from 2013 to the present have produced widely varying estimates of the probability of this failure mode, making it difficult to proceed with a decision to modify the structure. To address this uncertainty, physical hydraulic models are being tested in a conservative configuration that assumes no bonding between RCC lifts. The results will define the threshold conditions for failure, which will enable effective future evaluation of this potential failure mode at similar facilities.