Abstract: To better predict the impacts of tailings pond breaches and quantitatively understand the breach process and downstream effects, we prepared a composite model sand by mixing fine-grained tailing sand and expanded perlite in a 1.5:1 volume ratio. Indoor tests and measurements of underwater angle of repose confirmed the feasibility of the composite model sand under similar conditions. Based on this, we conducted large-scale overtopping dam failure tests under extreme conditions to analyze the changes in dam breach process, flow process, section morphology evolution, phreatic line, inundation elevation and range. The physical model test lasted 140 minutes, during which the composite model sand discharge accounted for 10.76% of the total storage capacity, and downstream siltation accounted for 95.21% of this discharge. These results are consistent with the real-world situation of overtopping failure, demonstrating the reasonability and effectiveness of the composite model sand for more realistically simulating tailings pond breach processes. These findings also offer new insights for selecting model sand in future overtopping failure tests for tailings pond.

Key words: composite model sand, tailings pond, overtopping dam failure, model test, phreatic line