Fracture law of different overlying strata in mining of protective seam under close distance coal seam

Abstract

AbstractTo study the fracture law of different overlying strata during mining of the lower protective seam under a close distance coal seam at a depth of 1000 m, roof bed‐separation and fissure imaging monitoring were carried out in the inlet roadway ahead of the working face of the JI15‐31040 lower protective seam in the Pingdingshan XII coal mine. The results show that with the overlying strata of the lower protective seam being affected by mining, the displacement of the overlying strata in the roof of 0–4 m was relatively large, and the fissure development was very significant. The displacement of the overlying strata in the roof of 4–12 m was relatively small, the fissures in this range were mostly randomly closed fissures, and this area was stable. Bed separation occurred in the roof of 12–16 m, and the bed‐separating fissures were mostly located at the coal–rock junction. During the mining process, the fractal dimension of the roof gradually increased, and the fissure network developed continuously. The changing process of the fractal dimension of the roof can be roughly divided into three typical change areas: less influence area (distance from the working face > 70 m), rapid increase area (15 m < distance from the working face < 70 m), and stable area (distance from the working face < 15 m), and the area within 70 m in front of the working face was the key supporting area. Under the influence of mining, the roof fissures showed an overall change trend of “from zero to some, from short to long, from small to large, and from narrow to wide.” This study can provide a reference for mining of the protective seam in deep coal seams.