Rainfall-induced instability mechanisms and slope angle optimization in open pit mines

Unreasonable design of the slope angle of the open pit mine is one of the main causes of slope instability, and this issue is particularly prominent under rainfall infiltration conditions. Therefore, designing a scientific, economical, and reasonable slope angle based on the failure mechanism of open pit mine slopes is of great significance for the mining safety and long-term stability of open pit mine slopes. This paper aims to propose an MSARMA slope angle optimization method with simple calculation and wide applicability and verify its rationality by utilizing the characteristics of constant-resistance large-deformation (CRLD) anchor cables that can monitor slope stability. Relevant research was carried out by taking four hazardous profiles of the Antaibao Open-pit Coal Mine in China as examples. The results show that slope instability under rainfall infiltration conditions can be divided into four stages through numerical simulation analysis combined with the actual on-site failure process: surface scouring, surface settlement, crack propagation, and shear slip. The slope angles were optimized for the four hazardous profiles with historical landslide occurrences, and the optimization results were verified using field monitoring data. When the slope angles of A-Aʹ, B-Bʹ, C-Cʹ and D-Dʹ dangerous sections are 34°, 32°, 33°and 33° respectively, the safety, stability, and economic rationality of the slope can be guaranteed. This study provides a theoretical basis and practical reference for slope angle optimization under similar engineering geological conditions.