Parameter optimization design of reconstructed sand cushion layers for inner dumps in open-pit mines

Residual water in the surrounding rock is a key factor that affects the slope stability of inner dumps in open-pit mines. Existing research on groundwater seepage in inner dumps has mainly focused on analyzing the effects of individual factors, such as rainfall or water level fluctuations, on slope stability. However, a comprehensive research framework for water prevention and control schemes under the combined influence of residual water in surrounding rock and groundwater recharge has not yet been established. To address this issue, taking an open-pit mine in the Thar Coalfield of Pakistan as the research background, a treatment scheme involving the reconstruction of the sand cushion layer at the base of the inner dump was proposed. The sand cushion in the inner dump was reconstructed into a four-layer structural system composed of waste material, sand cushion, impervious layer, and the third aquifer. The SEEP/W seepage model and the SLOPE/W stability model were established using GeoStudio software. The variations in seepage field and slope stability of the inner dump were compared and analyzed under conditions of different thicknesses and permeability coefficients of the reconstructed sand cushion. The results showed that increasing the permeability coefficient and thickness of the sand cushion could effectively lower the groundwater level in the inner dump and improve the overall slope stability. A reconstructed sand cushion with a thickness of 11.5 m and a permeability coefficient of 23.8 m³/d, or one with a thickness of 5.2 m and a permeability coefficient of 47.6 m³/d, enabled the slope stability coefficient to meet the required safety reserve factor.