Effect of Berm Properties on Non-Cohesive Earth Dam Failure due to Overtopping

Berms are typically built on the upstream and downstream slopes of earth dams to provide slope stability against seepage. The influence of berm properties on dam stability is widely studied in much research. The most important thing during dam failure by overtopping is to delay its failure and reduce maximum outflow discharge to give the region downstream chance to evacuate. In this paper, the effect of cutting berm with varying widths and heights on the erosion process, delaying the dam failure and reducing maximum outflow discharge during an overtopping event is experimentally investigated. The mean goal is to find the optimum berm width and height which give the best results of time of dam failure and maximum outflow discharge. To fulfill this goal many experiments are conducted and for each one, the erosion process, the time of dam failure, maximum outflow discharge and its time are measured and analyzed. In addition, two experiments lining the downstream slope are performed. The results revealed that constructing a berm with relative width equal to 0.33 and a relative height equal to 0.5, increases the time of dam failure by 12.5%, decreases the maximum outflow discharge by 2.22%, and increases the time to maximum outflow discharge by 25%. Also, it is found that the relative berm height ranges from 0.5 to 0.67 gives the optimum results. However, it is found that lining the upper part of the downstream slope and crest improves the results for relative berm heights less than 0.5. Lining significantly increases the time of dam failure by four times more than the case without lining and greatly delays the occurrence of maximum outflow discharge.