Roof control effect of in situ strip interval paste backfill in goaf

Faced with the dual challenges of coal mining under buildings, railways, and water bodies, as well as the shortage of backfill materials, and guided by the basic principles of more mining, less backfilling, and effective roof control, a technical concept of dip and strike in situ strip interval paste backfill mining in goaf was proposed, and a mechanical model of collaborative roof control was established for dip backfill and strike backfill. Also, the effects of main controlling factors such as uniformly distributed load on overburden, elastic foundation coefficient of filling body, filling body width, and backfilling spacing on the deflection and bending moment of the immediate roof were discussed, multivariate non-linear regression equations were developed for main controlling factors and maximum deflection and bending moment of the immediate roof, and design schemes of strip interval paste backfill parameters were proposed. Based on the geological conditions of a mine in Qipanjing Town, the optimized parameters of dip and strike strip interval paste backfill were calculated theoretically and then validated through FLAC^3D numerical simulation. The results demonstrated that uniformly distributed load on overburden had the most significant impact on the deflection and bending moment of the immediate roof. All the dip backfilling regression equations had a coefficient of determination R² greater than 0.996, while all the strike backfilling regression equations had a coefficient of determination R² greater than 0.999, indicating a good fit; the relationship between the filling body width and critical backfilling spacing followed a power function. As the filling body width increased, the critical backfilling spacing gradually increased, but the rate of increase decreased. For the mine in Qipanjing Town, when the filling body width was 6 m, the dip and strike critical backfilling spacings were 10.49 and 10.58 m, with the minimum backfill rates of 36.39% and 36.19%, respectively; the numerical simulation results are consistent with the theoretical analysis results, which further verifies the accuracy of the mechanical model.