Roof breaking mechanism of longwall stope with steeply dipping contugous coal seam group

The roof of the lower coal stope is subjected to repeated loading and unloading during the mining of steeply dipping contugous coal seam group. The characteristics of overlying rock migration and gangue filling are more complicated than those of a single coal seam. Taking the steeply dipping contugous coal seam group of Dongxia Coal Mine as the research object, physical similar material simulation experiment, theoretical analysis and field measurement were combined. The roof’s location was prone to bending and breaking is determined by establishing a fixed beam model based on the bottom coal stope roof. They were used to study the roof failure characteristics. The results show that the accumulation of caving roof in upper coal goaf is unbalanced along the inclination. There are differences in the contact degree between the collapsed and residual roof. The caved overlying rock can be divided into complete incline masonry areas and missing prone masonry areas along the vertical rock layer. The bottom load of the upper coal face presents zoning characteristics along the dip, according to the asymmetric filling characteristics of caving roof, it can be divided into gangue free filling area subject to approximate point load and middle and lower gangue filling area subject to disequilibrium. When the lower coal is mined, the inclined upper roof of the stope damages, slides down and fills the lower goaf. This leads to smaller bending moment of the lower stope roof and larger bending moment of the inclined middle and upper roof, in which the inclined middle and upper roof is more likely to break. Due to the different filling degree of goaf, the roof weighting of lower coal stope is larger in the middle part, followed by the upper part and smallest in the lower part. Compared with single coal seam mining, the intensity of periodic pressure in lower coal seam mining is low and the regularity is inconspicuous. The research can provide theoretical support for the roof stability control of longwall stope of steeply dipping contugous coal seam group.