Failure characteristics of thick hard roof stratum under hydraulic pre-splitting and its application in a coal mine, Dongsheng mining area

Due to the presence of the hard suspended roof, it cannot collapse naturally after the coal seam is mined. If the roof strata are suddenly destroyed without human intervention, it will cause serious geologic disasters. In this paper, we discuss the mechanisms and applications of hydraulic fracturing in alleviating the potential for catastrophic disasters. After preliminary analysis of fracturing crack propagation law, we investigate the failure and stress characteristics of overburden with and without fracturing, taking a coal mine in Dongsheng mining area as an example. The results show that the hard roof suffers severe damage after fracturing, and the initial rupture distance of the hard roof is reduced to about 40.0 m. Besides, the development height of the water-conducting fissure zone is approximately 138.18 m. The fracturing effect can be preliminarily speculated according to fluid pressure change curves. It is inferred that hydraulic fracturing point 3 has the best fracturing effect on hard-suspended roofs. On the other hand, we find the most overburden at the monitoring sites essentially bear compressive stress in fracturing and non-fracturing conditions, and a common trait of overburden stress is easily observed, namely, that overburden stress after fracturing shows a relatively smaller value than that of non-fracturing condition, and the overburden stress reduction is more significant at the goaf center and near the stopping site. The study provides theoretical support for the safety management of thick hard roofs, especially in the coal mines seriously affected by roof accidents.