Research on overburden failure and prediction of water-conducting fracture zone in underlying coal seam mining under burnt rock in reservoir area

After the extraction of the 5⁻² coal seam beneath the Changjiagou Reservoir at the Zhangjiamao Coal Mine, accurately understanding the failure characteristics of overlying burnt rocks and the development height of water-conducting fracture zones on the working face is essential to ensure safe and efficient production and implement environmentally friendly water-preserving mining practices. Taking the overlying rocks of the 15205 working face of the 5⁻² coal seam as the research object, a study is conducted on the movement characteristics of the overlying rocks and the height of the water-conducting fracture zones on this working face through model experiments and on-site measurements. Based on the measured data of existing water-conducting fracture zones in the Zhangjiamao Mining Area, a nonlinear prediction model suitable for the height of water-conducting fracture zones below the water body in the 5⁻² coal seam is constructed. A comparative analysis is conducted with the results of model experiments and on-site measurements. The research results show that the on-site drilling results indicate that the height of the water-conducting fracture zone on the coal seam working face ranges from 75.20 m to 75.60 m, with a fracture-to-mining ratio of 12.53 to 12.60. According to the mining area hydrogeological engineering geological exploration norms, the calculated height of the water-conducting fracture zone on the coal seam working face is 74.12 m, with a fracture-to-mining ratio of 12.35, resulting in an error of 1.7%. The similar model experiments yield a height of 84.5 m for the water-conducting fracture zone on the coal seam working face, with a fracture-to-mining ratio of 14.08, resulting in an error of 12.0%. Integrating the research results of the existing water-conducting fracture zones in the mining area, a predictive model is established to calculate the height of the water-conducting fracture zone on this working face, resulting in a height of 74.48 m and a fracture-to-mining ratio of 12.41, with an error of 1.2%. The predictive model can reflect the actual distribution law of water-conducting fracture zones in the overlying burnt rocks of the 5⁻² coal seam, demonstrating good accuracy and engineering applicability, and providing a reliable basis for water hazard prevention and control in this coal seam.