Study on the characteristics and formation mechanism of overtopping failure of fine-grained molybdenum tailings dam

• A fine-grained tailings dam model was constructed with the similarity of water flow conditions and sediment movement conditions as the core. Based on the erosion characteristics of the fine-grained tailings dam body and the water flow characteristics during the flood overtopping process, the failure process of the fine-grained tailings dam was divided into four stages. The changes in the overtopping flow and the erosion process in different stages were quite different. • Through the analysis of the characteristics of tailings dam failure, it is clear that the overtopping flow is greater than the infiltration flow, which leads to runoff on the tailings dam surface. Therefore, reinforcing the tailings dam surface is an effective means to improve the toughness of the tailings dam. • Based on the sediment diffusion equation and hydrodynamic principles, the overtopping failure process of fine-grained tailings dams (break formation-expansion-scour) elucidates the generation mechanism of overtopping failure of fine-grained tailings dams. Tailings dams, owing to their distinctive construction methodologies and mechanical characteristics, are susceptible to inducing high-potential-energy and highly hazardous anthropogenic debris flows upon dam breaching, thereby jeopardizing downstream safety. With the ongoing advancement of mineral beneficiation technologies, tailings particle sizes are progressively diminishing annually. Given the substantial disparities in properties between fine-grained tailings and medium- to coarse-grained tailings, a comprehensive comprehension of the overtopping erosion process is imperative for facilitating the reutilization of fine-grained tailings and developing fine-grained tailings dam construction technology. Based on a self-designed overtopping dam failure test device, this paper studies the overtopping failure process of fine-grained tailings dams under different breach patterns, and explores the breach formation and expansion mechanisms. The results show that: (1) the occurrence of runoff on the dam surface is the direct cause of tailings dam failure; (2) based on the dam body morphology and erosion characteristics, the tailings dam overtopping failure process can be divided into four stages: pre-failure (gully formation), mid-failure (gully expansion and connection), late-failure (internal erosion), and final-failure (headwater erosion); (3) during the entire failure process, the overtopping flow showed three peaks. The pre-set breach increased the flow of the first two peaks by an average of 16.3% and 11.47% compared to the case without a breach, while the flow of the last peak decreased by 37%; (4) considering the scouring characteristics of the overtopping flow, reinforcing the dam slope is an effective means to improve the toughness of tailings dams. The relevant results can provide a reference for enhancing the toughness of fine-grained tailings dams.