Regularity and control of overburden and surface fractures in shallow-contiguous seams

The Shenfu-Dongsheng Coalfield in western country mainly occurs in shallow close multi-seam, and the thick loose layers on the overlying rock are distributed in a wide range. Mining in shallow-contiguous seams results in serious development of overlying rock and surface fractures, which aggravates the deterioration of the originally fragile ecological environment. In order to explore the mining-induced overburden and surface fractures development characteristics in shallow shallow-contiguous seams, and obtain its control method. Taking No.1^-2 seam and No.2^-2 seam mining in Ningtiaota Coal Mine as background, this paper obtains the development characteristics of fractures in shallow single seam mining and repeated mining through in-site statistic analysis, physical simulation and fractal theory. Besides, the control effect of pillar staggered distance to mining-induced fractures is revealed. The results show that the mining-induced surface fractures can be divided into two types, one is dynamic fractures which are parallel to the working face, and another is mining boundary surface fractures which contain open-off boundary surface fractures and pillar boundary surface fractures. The dynamic fractures can realize self-repairing after mining, while the mining boundary surface fractures can not realize self-repairing. After lower seam mining, the pillar boundary overburden and surface fractures development seriously, which are closely related to pillar staggered distance. After No.1^-2 seam mining, the bedrock caving angle is 60°, and the soil layer caving angle is 65°, the width of surface fracture along coal pillar, 0.26 m. After lower No.2^-2 seam mining, when the pillars are aligned, with pillar staggered distance of 20 m and 40 m, the width of overburden fractures are 0.81 m, 0.45 m and 0.22 m respectively, and the width of surface fractures are 0.65 m, 0.30 m and 0.12 m. Through determining the reasonable pillar staggered distance, development of the overburden and surface fractures can be controlled effectively. Finally, the reasonable pillar staggered distance should be greater than 40m in No.1^-2 and No.2^-2 seams mining in Ningtiaota Coal Mine.