Strata Movement Prediction for Safe Recovery of Vertical Shaft Protection Coal Pillars During Backfill Mining

The safe and efficient recovery of shaft protection coal pillars is a critical issue in coal mining engineering. Backfill mining, which replaces underground coal resources with solid waste materials, provides an effective approach for controlling strata deformation and improving resource recovery. In this study, a strata movement prediction model for backfill mining was established based on elastic foundation theory and similarity transformation assumptions. Numerical simulations were conducted to investigate the evolution characteristics of strata subsidence boundaries, and the boundary constraint function of the prediction model was derived through inversion. The effects of backfill porosity on the strata subsidence range were analyzed. The results indicate that the strata subsidence boundary point exhibits a logarithmic relationship with strata burial depth. Under a backfill ratio of 90%, reducing the porosity of backfill materials can effectively decrease the subsidence range of overlying strata. The proposed strata movement prediction model was applied to an engineering case to evaluate the effectiveness of shaft protection coal pillar recovery. Results show that although the strata damage angle under backfill mining is smaller than that under caving mining, the height of the strata affected by critical damage deformation is significantly reduced. By adopting backfill mining, the required width of the ventilation shaft protection coal pillar is reduced by 301.5 m, which significantly improves the mining recovery rate.