Evolution of the roof caving and fracture zones during mining of close range coal seams

This study employs an integrated methodology combining slip line field theory, FLAC3D numerical simulation, and hydraulic injection testing to systematically investigate the evolutionary characteristics of roof two zones under repeated mining conditions in close range coal seams No.9 and 10 (average interburden thickness is 10.2 m). Theoretical modeling reveals a maximum failure depth of 6.26 m in the No.9 coal seam, with corresponding caving and fracture zone heights measuring 9.6 m and 33.4 m respectively. Numerical simulations demonstrate that subsequent extraction of the No.10 coal seam induces fracture zone expansion to 66 m vertical elevation, representing a 73% increase relative to single-layer mining conditions. Strong congruence was confirmed through MATLAB-based regression analysis. Hydraulic injection tests substantiate the spatial heterogeneity of two zones (caving zone and fracture zone) development, while mechanical analysis proposes a stress arch-dominated fracture propagation mechanism. These findings establish a mechanical framework for safe extraction of close range coal seam clusters, successfully informing optimization of combined bolt reinforcement and grouting curtain configurations in practical applications.