Understanding Geotechnical Embankment Washout Due to Overtopping: Insights From Physical Tests

Abstract Understanding the erosion process of an earth dam and flood embankment composed of noncohesive, homogeneous soils due to overflow is crucial for determining the quantity and rate of water release. This is necessary to assess the consequences of a failure, analyze the risk, and develop appropriate crisis management procedures. Despite numerous studies in this area, the process of breach evolution is not fully explored. The article presents the results of physical experiments carried out in the field laboratory of the Wrocław University of Science and Technology for a dam with a height of 0.50 m that closes a reservoir with a capacity of 14.4 m 3 , whose width is significantly greater than the final width of the breach. The scenario analyzed assumes that water overflows the embankment crest, as it is the most common cause of embankment failure based on dam disaster databases. At the same time, the amount of water accumulated in the reservoir is the largest possible for this scenario, suggesting that such a catastrophe may have the most severe consequences. Based on the results obtained from three experiments, four repeatable phases of erosion evolution were identified and described: (I) the initiation phase, (II) the vertical erosion phase, (III) the lateral erosion phase, divided into two cycles, and (IV) the reservoir emptying phase without further propagation of the breach. The outflow rate of the water from the reservoir was also analyzed, allowing the determination of the outflow hydrograph for each test. Hydrographs showed differences between individual experiments; however, the average erosion rate was similar for all tests. Furthermore, the final width of the breach created each time was between 2.2 and 2.5 H (where H is the height of the embankment) and the volume of eroded soil ranged from 0.52 to 0.59 m 3 . The article also highlights the methodology to calculate the water outflow hydrograph.