A Case Study: Determination of the Optimal Tailings Beach Distance as a Guideline for Safe Water Management in an Upstream TSF

Most tailings storage facility (TSF) failures occur in active, upstream-type TSFs, often due to extreme and unexpected weather conditions—specifically, heavy rainfall and strong winds. This case study of a TSF in southern Arizona examines the use of the optimum safe beach distance (D_optimal, the optimum distance between the crest and decant pond) as a tool for monitoring geotechnical stability and reducing catastrophic failures. A digital model of the TSF was used to determine the critical beach distance (D_critical) under normal weather conditions, and D_optimal was then determined by adding incremental distances to account for the effects of heavy rainfall (D_rainfall) and strong winds (D_wind). To overcome accessibility issues, a drone was used to map the TSF geometry and create a digital model. This model served as the basis for conducting a coupled stress-seepage, finite-element (FEM) analysis with a safety factor of 2.0 to assess geotechnical stability (D_critical). The safe beach distance increments were determined using the PMP (probable maximum precipitation) and possible maximum wind speed. Based on this analysis, the optimal safe beach distance at the study site was identified as 202.2 m. Since the current beach distance (371 m) exceeds this value, the TSF was considered to be stable and satisfied the design safety factor of 2.0. However, this distance should be reassessed periodically to account for changes in the TSF geometry and other conditions. Furthermore, it applies only TSFs that are well-managed and feature a smooth, non-undulating beach surface with a consistent slope.