Differential Effects of Rainfall Temporal Distribution on Tailings Dam Stability: A Comparative Study of Two Storm Types in the Poyang Lake Basin

Tailings dam safety is a cornerstone of green and sustainable mine development. The instability of such facilities directly threatens the safety of surrounding ecosystems, human lives, and property, contravening the Sustainable Development Goals regarding clean water and terrestrial ecosystem protection. Rainfall is the primary external factor triggering tailings dam instability, yet the failure mechanisms may differ fundamentally depending on the temporal distribution of rainfall. Against the background of the Poyang Lake Basin, this study integrates observed rainfall data from 2020 to 2025 with a survey of 101 active tailings dams (of which Class IV dams account for 43.6% and upstream-method construction accounts for 88.1%), on the basis of which a representative Class IV upstream-method tailings dam is selected as the prototype. A coupled unsaturated seepage and stability numerical model is constructed, and two sets of rainfall scenarios are designed: one varying the rainfall peak position coefficient t and the other varying the rainfall duration. The results indicate that infiltration induced by short-duration intense rainfall is confined to shallow strata. The earlier the rainfall peak, the more fully the deep infiltration develops and the greater the factor of safety reduction, with the critical variable governing stability degradation being the length of time available for deep redistribution after the rainfall peak. Long-duration sustained rainfall drives an overall rise of the phreatic line, and the seepage response is dominated by the average rainfall intensity. Extending the duration cannot compensate for the attenuation of the infiltration driving force caused by the reduced rainfall intensity, and the core factor determining disaster risk is whether the average rainfall intensity can exceed the drainage threshold of the deep low-permeability layers. Within the Poyang Lake Basin, concentrated heavy continuous rainfall during the Meiyu period lasting 20 to 40 days represents the decisive working condition governing tailings dam stability and should be prioritized in flood-season safety supervision. The rainfall-driven instability mechanisms revealed in this study provide a theoretical basis for establishing differentiated monitoring and early-warning thresholds and for the sustainable operation of tailings dams.