Efficient gas extraction from roof of overlying limestone stoping face

In order to explore the gas storage state and extraction scheme under the conditions of limestone roof, X-ray diffraction experiments of limestone were carried out. The physicochemical properties of limestone were studied, and the influence of limestone on the roof gas storage and gas extraction was analyzed. The 90107 working face of Changxin Coal Mine in Qinyuan, Shanxi was used as the engineering background. The height of the "two belts" of the roof was calculated by empirical formula theory, and then the failure morphology and fracture development characteristics of the roof in the process of coal winning were analyzed in combination with 3DEC numerical simulation software. The gas extraction scheme of high-level directional drilling was designed according to the advantage area of roof fissure development and verified by on-site measurement. The study shows that with the advance of the working face, the initial collapse step width of the roof is 40 m, the cycle collapse step width is 40 m, the height of the caving zone is 11.4 m, the development height of the fractured zone is 50 m, and the advantage area of fissure development is from 11.4 m to 25.0 m. The on-site measurement finds that the problem of gas exceeding limit in upper corner angle and working face is effectively solved. After the extraction, the gas concentration in the upper corner gas remains below 0.8%, and the maximum decrease of gas concentration in the upper corner is 87.5%. The research results provide a reference for efficient gas extraction under similar limestone geological conditions.