Model tests and numerical simulation of overtopping-induced breach process of the asphalt concrete core dam

Although asphalt concrete core dams have been widely constructed, the mechanism of overtopping-induced dam breaches during catastrophic floods remains unclear, especially concerning the structural failure process of the core wall. This study utilizes a flume model test system to examine the overtopping-induced breach process of an asphalt concrete core dam based on the Sheyuegou Dam breach case in Xinjiang, China. The model tests showed the continuous erosion of dam shell material and structural failures of the core wall during dam breaching, highlighting the significant impact of the erosion-resistant asphalt concrete core wall on the dam breach process. The overtopping breach process of an asphalt concrete core wall dam can be divided into three stages: the asphalt concrete core wall is gradually exposed by backward erosion of the dam shell material until the first structural failure occurs; one or multiple structural failures of the core wall happen due to breach enlargement by continuous erosion of dam shell material until peak breach flow is reached; multiple structural failures of the core wall take place as the breach in the dam shell deepens and widens until breach morphology stabilizes. A numerical model is developed to simulate the overtopping-induced breach process of the asphalt concrete core dam based on the breach model tests. This model utilizes a soil erosion formula to estimate the dam shell material's erosion rate and calculate the exposed length of the asphalt concrete core wall. In addition, the moment balance method is employed to determine the overturning moment and length at each structural failure and the overturning instances of the exposed core wall due to hydrodynamic force and soil pressure. A notable feature of the numerical model is its ability to depict the coupled effects of soil erosion and structural failures of the asphalt concrete core wall during dam breaching. This numerical model is applied to a back analysis of the Sheyuegou dam breach process. The comparison between measured and calculated results indicated that the breach hydrograph and breach evolution process accurately represent the actual breach process of the Sheyuegou dam, with the relative errors of essential dam breaching parameters remaining within ±25 %. Sensitivity analysis showed that the thickness variation of the asphalt concrete core wall significantly influences the dam breach process, with the order of impact on critical breaching parameters being time to peak, final breach size, and peak breach flow. The results provide valuable insights into the simulation of the overtopping failure process of asphalt concrete core dams.