Water outbursts in underground mining with steeply dipping coal seams: numerical simulations based on a mining case

The height of the water-conducting zone is of significant importance for the safety of underground mining under a water body. Fully backfilling a mine excavation with gangue provides the advantages of safety and efficiency during the extraction of coal under buildings, railways and water bodies. Based on a mine with steeply dipping coal seams, a systematic numerical study of the damage mode of the safety pillar and roof strata surrounding a stope with and without backfilling was performed. The fracture initiation, propagation and coalescence in the stressed strata, and the seepage fluid field evolution were numerically obtained during the advance of the working face, which provided the detailed evolution of the fracture zone and the interaction of the fractures surrounding the stope in the steeply inclined coal seam. When backfilling with gangue is used as part of the mining process, the degree and absolute values of roof strata deformation are clearly reduced. The safety of the pillar and roof strata are all characterised by a transition from uniaxial compression to biaxial compression, which evidently improves their stability. The damage around the safety pillar and the height of the mining-induced fracture zone in the roof strata are then effectively restrained. Because of the technical advantages of backfilling with gangue in steeply inclined coal seams, the backfilling technology is easy to apply and may result in good support of the overlying strata. The higher the stiffness of the backfill is, the lower the amount of subsidence and damage to the roof strata will be. Because the stress concentrations and deformation around the working stope are reduced, the backfilling is beneficial to the stability of the safety pillar in the current working stope and to worker safety in other stopes and adjacent coal seams. These findings may provide technical data for engineering designs and safety evaluations in similar coal mines.