Three-dimensional void fraction evolution law and sensitivity analysis of mining-induced overburden based on...

The voids in overlying strata caused by coal mining are prone to induce geological hazards. To reveal the evolution of overburden voids, a three-dimensional dynamic void fraction (VF) model based on the Bertalanffy time function was constructed and verified. Four evaluation indicators were proposed: the average VF of the caving zone, fracture zone, and separation zone (AVF-CZ, AVF-FZ, AVF-SZ), as well as the bulk average VF of the entire mining-induced overburden (BAVF-EMO). The influence of four main controlling factors-mining height, working face length, distance from the main roof to the coal seam, and distance from the sub-key stratum (SKS) to the coal seam-on these indicators was analyzed. The results show that with increasing mining time, the VF of the caving zone gradually decreases, whereas the VF of other zones gradually increases and stabilizes after 80 days of advancement. When the mining height exceeds 5 m, both AVF-CZ and BAVF-EMO decrease significantly; for every 100 m increase in the distance between the SKS and the coal seam, AVF-FZ and AVF-SZ increase notably. The research findings can provide a theoretical basis for selecting backfilling parameters and for preventing and controlling mining-induced hazards.