Study on isolation pillar thickness optimization and slope stability control in hanging wall ore mining

Aiming at the problems of easy disturbance to the overlying slope and difficulty in scientifically determining the thickness of the isolation pillar during the recovery of hanging-wall orebody under open-pit to underground mining conditions, this study takes Shizhuyuan Mine as the engineering background. FLAC3D numerical simulation and the strength reduction method (SRM) are adopted to conduct a comparative analysis of the stability response characteristics of the "slope-goaf-backfill" system under five working conditions with isolation pillar thicknesses ranging from 10 m to 50 m. The results show that although the safety factors of all working conditions meet the requirements for Grade I slope stability, the thickness of the isolation pillar exhibits a significant threshold effect on system deformation control: when the thickness increases to 30 m, the maximum system displacement is significantly reduced from the excessive level (> 80 mm) to approximately 34 mm, and the overall stability is obviously improved. However, the stability gain brought by further increasing the thickness gradually weakens. Under the recommended thickness, the stress distribution, displacement evolution, and plastic zone development of the goaf and backfill are all within the safe and controllable range. Considering both stability requirements and resource recovery rate, an isolation pillar thickness around 30 m can achieve a reasonable balance between safety and economy, which can provide a quantitative design reference for the safe recovery of hanging-wall orebodies under similar open-pit-underground coordinated mining conditions.