Abstract
The hydrogeological conditions of the Qianbei coalfield are complex, and karst water in the roof rock frequently disrupts mining operations, leading to frequent water inrush incidents. Taking the representative Longfeng Coal Mine as a case study, this paper analyzes the structural characteristics of the overlying roof strata. By calculating the stratum stretching rate, the theoretical development height of the water-conducting fracture zone is derived to be 51 meters. Numerical simulations were used to study the stress field, displacement field, and plastic zone distribution patterns in the overlying roof strata. Combined with similar simulation tests and digital speckle experiments, the spatiotemporal evolution characteristics of the water-conducting fracture zone were investigated. The results indicate that the fracture zone exhibits a "stepped" development pattern, with the fracture morphology evolving from vertical to horizontal. Near the goaf boundary, the strain gradually decreases, and the instability of the key stratum may lead to the closure of separation fractures or the redistribution of water-conducting fractures. Field measurements of the water-conducting fracture zone show that post-mining roof fractures can be classified into tensile-shear, through-going, and discrete types, with decreasing water-conducting capacity in that order. Finally, the study systematically elucidates the disaster mechanisms of dynamic and hydrostatic water inrush in the Longfeng Coal Mine from the perspective of key stratum instability. The findings provide valuable insights for water prevention and control efforts in the Qianbei coalfield mining areas.