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Abstract Based on the mining conditions of shallow close coal seams in the Jurassic coalfield of northern Shaanxi, in order to explore the evolution and development height prediction of water-conducting fracture zone (WCFZ), combining with measured statistical analysis, physical simulation, numerical calculation, and theoretical analysis, the evolution of mining-induced fractures and the development characteristics of WCFZ are analyzed, and the development height predicting method of WCFZ in shallow close coal seams mining is proposed. The results show that in shallow single coal seam mining, during the stage of incritical mining, the height of the WCFZ increases in a “jumping” pattern with the main roof periodic caving. After critical mining, it is basically stable. Its development height is positively correlated with the mining height. The ratio of development height to mining height is generally 20–30, and the change is not significant with the mining height, overall, the distribution of the WCFZ is “saddle shaped”. Based on close distance coal seams repeated mining, the primary fractures act as activation development when the interburden broken completely, the development of WCFZ at the mining boundary is significantly intensified, and ratio of the height to mining height in repeated mining is obviously lower than that in single seam mining, which is generally 18–25. The traditional empirical formula cannot be applied to the development prediction in shallow close coal seams mining, with an error of 10–50%. Considering the mining height, interburden thickness, and roof caving characteristics, the development height predicting method of WCFZ in shallow close coal seams mining is proposed. Compared with measured results, the calculation error is basically within 15%, which has good prediction accuracy, The research results can provide a theoretical basis for predicting the height of WCFZ in shallow close coal seams mining in the Jurassic coalfield of northern Shaanxi.

In multiple seam coal mining, the fractures induced by the mining of the lower coal seam may propagate to the goaf of the upper coal seam that is mined earlier. The fracture connection leads to the leakage of hazardous gas. To fully understand the gas leakage due to fracture evolution, the electromagnetic-based measurement system and the borehole televiewer were adopted in the panel No.8100 in Tongxin coal mine, Datong Coalfield, China. The coal seam thickness is 15 m and it was mined by top-coal caving method. The resistivity and fracture pattern in distinct zones of rock stratum were detected, and the correlation between them was explained clearly. We found that the fracture evolves in two stages as the panel working face advances, i.e., fracture propagation and fracture re-closure. The maximum height of fracture propagation is 150 m, in which the height of the caved and the fractured zones are 80 m and 70 m, respectively. These fractures start to be compacted and are re-closed at the distance of 80 m behind the working face. The extraction of the panel No.8100 results in the formation of a gas-bearing zone (GBZ) with separations and shear fractures rather than connecting the goafs of the carboniferous coal seam (CCS) and the jurassic coal seam (JCS). The GBZ is located in a region from 80 m to 150 m above the goaf and 80 m behind the working face. Based on the above findings, effective gas drainage approach is proposed to reduce the concentrations of the hazardous gases consisted of CH4 and CO. After gas drainage, the maximum concentrations of CH 4 and CO drop to 0.5% and 16.63 ppm, with reductions of 53.7% and 33.9% respectively. • Fracture evolves in two stages, i.e., fracture propagation and fracture re-closure. • The CCS goaf did not connect the upper JCS goaf. • The extraction of the longwall panel results in the formation of a GBZ. • EH-4 detection provided important geological information for coal mining. [ABSTRACT FROM AUTHOR]