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Coal bump seriously threatens the safe and efficient mining of coal, and the research on the occurrence mechanism of coal bump is of great significance. The roadway coal bump accounts for 86.8% of the total. The occurrence of coal bump in gateroad is summarized. It is considered that hard roof and hard coal are the geological characteristics of coal bump, and the sliding instability of rib coal mass is the failure characteristics of coal bump. Based on the elastic foundation theory, the upward deflection characteristics of the front and lateral roof of the working face under the condition of hard roof are analyzed, and compared with the engineering practice of roof rebounding. Taking the roadway coal mass as the research object, the unloading sliding mechanical model of roof-coal-floor composite structure is established. By analyzing the relationship between horizontal ground stress of coal mass, frictional force of coal-roof and coal-floor and tensile resistance of coal mass, the critical equation of coal bump is established. It is proposed that the vertical pressure of coal seam is reduced due to the upward deflection of the roof, and the coal mass loses its clamping and moves into the roadway after overcoming the friction between roof and floor and the tensile strength of coal mass under the action of horizontal ground stress, that is, the unloading and slippage mechanism of coal bump in hard roof mining roadway. The model reasonably explains the causality of coal bump in hard roof mining roadway. Based on the unloading-slippage model, the principle of influencing factors of coal bump, includes the buried depth, roof strength, roof elastic modulus and roof thickness, coal mass strength and elastic modulus. Finally, two coal bump events, "8.2" coal bump in Tangshan coal mine and "11.11" coal bump in Hongyang mine are analyzed and the unloading-slippage mechanism are the reasoning of two events. [ABSTRACT FROM AUTHOR]

The initial fracture and development of fracture under loading conditions of coal are closely related to the stability of surrounding rock and geo-dynamic disasters. In this study, nuclear magnetic resonance (NMR), acoustic emission (AE) and 3D-CAD reduction techniques were employed to analyze the initial fracture distribution, the fracture development and failure mode of coal samples with different strengths under uniaxial loading. Based on NMR and 3D-CAD reduction, the initial fracture rate and fracture distribution of coal samples were obtained. Through uniaxial loading and AE, the distribution of fracture points was analysed. The dominated fracture of the failure state was reconstructed using 3D-CAD. Results show the initial crack rate of hard coal is low, and the ringing accounts and AE energy are small in the initial stage of loading. However, they increase rapidly in the later stage of loading, showing the characteristics of brittleness. In the initial state, the fracture rate of soft coal sample is higher than that of hard coal, and the growth of fracture point is fast. In the later stage, the fracture point number and AE energy are similar to that of hard coal. The initial fracture rate and fracture distribution of coal with different strengths are different, resulting in different occurrence and development of secondary fractures in loading state, which indicates that the deformational behaviour, failure mode and energy release are different for coal with different strengths. This study provides a theoretical basis for the stability analysis and geodynamic disasters prevention of coal with different strengths. [ABSTRACT FROM AUTHOR]