Analysis and prevention of influencing factors of face end roof falling under repeated mining of short-distance coal seam group

The existing researches on face end roof falling are mostly focused on single coal seam, while the stability of the face end roof under short-distance coal seam group mining is different from that of a single coal seam. In the process of short-distance coal seam group mining, due to the small spacing between adjacent coal seams, the roof structure and stress environment of the lower coal seam mining area will change after the upper coal seam is mined. This easily lead to catastrophic problems such as face end roof falling, coal wall spalling and roof pressure frame. Taking the 17101 working face of a mine that has experienced 3 large-scale face end roof falling as the engineering background, based on the stability relationship between the coal wall, hydraulic support and the face end roof, the ‘face end roof-coal wall-support’ model is established under repeated mining of short-distance seam group. This paper introduces the main influencing factors of face end roof falling under repeated mining of short-distance seam group are the strength of the roof and surrounding rock, support working resistance, advancing speed and face end distance. The UDEC simulation software is used to simulate the influence of different influencing factors on the face end roof falling under repeated mining, and conclusions are summarized as follows. ① The face end roof and coal body are damaged during repeated mining, the strength of the face end roof and coal wall is reduced, and the face end roof at the front end of the support is prone to fall, causing disasters such as roof falling and coal wall spalling. As the strength of the roof and surrounding rock increases, the stability of the roof is better. ② The low working resistance of the hydraulic support is one of the important reasons for the face end roof falling of the working face. As the working resistance of hydraulic support increases, the stability of the face end roof is better. ③ The advancing speed of the working face has a significant effect on the stability of the face end roof. The slower the advancing speed of the working face is, the more serious is the roof subsidence phenomenon of the at the stope. ④ The tip-to-face distance is an important influencing factor of the face end roof falling. The face end roof falling is linearly related to the tip-to-face distance. The falling height increases with the increase of the tip-to-face distance. The smaller the tip-to-face distance is, the more stable is the face end roof. However, too short tip-to-face distance will also affect the normal mining of the working face. The tip-to-face distance should be determined according to the actual situation. In the context of the four main influencing factors, the prevention and control measures for face end roof falling under repeated mining are proposed. The measures include increasing the strength of the roof and surrounding rock, improving the working resistance of hydraulic support, controlling the advancing speed reasonably and reducing the tip-to-face distance. The above prevention and control measures can provide an effective solution for the face end roof falling under repeated mining of short-distance seam group.