(1. School of Energy and Mining，China University of Mining and Technology(Beijing)，Beijing 100083，China；
2. Beijing Key Laboratory for Precise Mining of Intergrown Energy and Resources，China University
of Mining and Technology(Beijing)，Beijing 100083，China)
Abstract：In order to study the three-dimensional fracture evolution characteristics of the main roof between adjacent coal seams，a mechanical model for the periodic fracture of the main roof plate structure with special-shaped load and elastic foundation was proposed to analyze the fracture position，fracture type and fracture pattern of the main roof. Moreover，spatial stability of the fracture structure was analyzed to discuss the instability conditions of the right-angle trapezoidal block and its response to the key factors. The results were as follow：(1) The fracture characteristics of the main roof are directly related to the distribution of the overlying load. When the load is uniform，an“O-X” shaped fracture appears on the main roof，which forms an isosceles trapezoidal block and two arc triangular blocks. When the roof is subject to a single peak load formed by boundary coal pillar and goaf，an“O- ”shaped fracture appears on the main roof，which forms two right-angle trapezoidal blocks and two arc triangular blocks. Meanwhile，when the roof is subjected to a bimodal load formed by isolated coal pillar，the fracture pattern of the main roof takes an“O- ”shape，thereby forming a crushing zone between the right-angle trapezoidal blocks. (2) According to the instability criterion of the fracture structure，instability forms of right-angle trapezoidal block include sliding instability and rotation instability，and each form can be divided into overall instability and one-side instability. (3) As the overlying load(q) increases，the sliding instability coefficient(K1 and K2) decreases，while the rotation instability coefficient(K3 and K4) increases，indicating that the increase of load(q) is not conducive to the safety of surrounding rocks. The law of the fracture width(w) is consistent with the overlying load(q). However，when the fracture width reaches a certain threshold，the sensitivity of block stability decreases. As the cycle weighting interval(l) increases，the sliding instability coefficients(K1 and K2) and the rotation instability coefficients(K3 and K4) increase，indicating that the increase of the weighting interval simply induces rotation instability. As the mining height of the lower coal seam(m2) increases，the corresponding sliding instability coefficients(K1 and K2) decreases，and the rotation instability coefficients(K3 and K4) increases significantly at the end of the rotation，indicating that the increase of the mining height adversely affects the main roof stability. (4) Field ground pressure monitoring and borehole detection verify the rationality and reliability of the mechanical model and theoretical analysis.
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2023, Vol. 42 
