Experimental Study on the Overtopping Failure Process and Mechanism of a Tailings Dam Under Continuous and Intermittent Rainfall

Using an upstream tailings pond in Beijing as the prototype, this study constructed a 1:150 physical model to investigate the internal response and overtopping failure evolution of tailings dams under continuous rainfall (T1) and intermittent rainfall (T2). The results showed that the cumulative rainfall duration at failure in T2 was approximately 11.1% shorter than that in T1. The duration from local overtopping to overall failure in T2 was 40% shorter than that in T1. Under T2, during the first rainfall interval, the average rise rates of the phreatic line, volumetric water content, pore water pressure, and earth pressure were approximately 0.35, 0.42, 0.29, and 0.32 times the corresponding rise rates under T1, respectively. During the second rainfall interval, the average decline rates of the phreatic line, pore water pressure, and earth pressure were approximately 1.83, 2.79, and 3.52 times the corresponding rise rates under T1, respectively. Overtopping failure under both rainfall patterns was a composite instability process controlled by internal seepage weakening and overtopping erosion. The process can be divided into four stages: toe seepage, dam deformation, local overtopping, and overall sliding failure. These findings indicate that rainfall pattern and internal response should be considered in tailings dam risk identification.