Study on the development of water-conducting fracture zones under repeated mining conditions

To clarify water-conducting fracture zones (WCFZ) development under repeated mining, this study focuses on Huayang Coal Mine's Working Face 15101, adopting an integrated multi-method framework (experimental testing-visual verification-theoretical simulation). Borehole water injection tests are conducted to obtain the variation of WCFZ's permeability coefficient and its developmental height; by observing fracture morphology through borehole television, a quantitative correlation between “permeability coefficient and fracture structure” is established. The study also utilizes theoretical calculations and numerical simulations to predict WCFZ height evolution, and systematically reveals the development characteristics of WCFZ under repeated mining and the law governing its influence on the permeability of overlying strata. Results indicate that the permeability coefficients of the caving zone and fracture zone are 4.9–8.2 and 1.6–4.6 times those of the original rock strata, respectively. This pattern is supported by the fracture morphology observed through borehole television. Numerical simulations find that mining the No. 15 coal seam increases the No. 9 coal seam's overlying WCFZ height by approximately 11.4%. With the study comparing field measurements (75.31 m), theoretical analysis results (68.87 m, approximately 8.6% lower), and numerical simulations (73.87 m, approximately 1.9% lower), the final WCFZ height after repeated mining is determined by field measurements. These findings improve understanding of repeated mining-induced WCFZ and guide roof water hazard mitigation in similar mines.