Study on the evolution law of bed separation and aperture variation in overlying strata under multi-coal seam superimposed mining

As deep coal mining expands,water damage resulting from roof separation during the overlapping extraction of multiple coal seams has become a significant hazard and a key research focus. This study examines the West 1st Mining Area of the Hongyang Coalfield to systematically analyze the spatial and temporal evolution and aperture variation of overlying strata separation under multi-seam mining conditions,by using similar materials, 3DEC numerical simulation and other means. The results indicate that the development of bed separation is strongly influenced by the rupture of key strata,interactions within the mining-induced stress field,and the sequence of seam extraction. High-level separation between coal seams 7to12 can reach a maximum aperture of 3. 5 meters under combined field effects,while immediate roof separation above coal seam 3 is limited to 0. 6 meters due to key stratum interaction. Based on these findings,a predictive model for bed separation aperture was developed, incorporating key stratum theory and the effects of rock fragmentation and bulking. Field measurements from working face 301 show that model predictions deviate by less than 15%.