Unloading-slippage mechanism of rock burst occurred in longwall roadway

Rock burst seriously threatens the safety and economy of coal mining industry. The causality mechanism research of rock burst is of great significance. The occurrence of roadway rock burst accounts for 86.8% of the total rock bursts. Based on the phenomena of rock burst occurred in roadway, this paper considered that hard roof and hard coal are the key geological characteristics of rock burst, and the sliding instability of rib coal mass is their specific failure attribute. 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 object, the unloading sliding mechanical model of roof-coal-floor composite structure is established. By analyzing the relationship between horizontal stress of coal mass, friction force of coal-roof and coal-floor and tensile resistance of coal mass, the critical equilibrium equation of rock burst is established. It is proposed that the vertical pressure of coal seam is reduced due to the upward deflection of roof, the underneath coal mass loses its clamping forces 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 stress. This is the unloading and slippage mechanism of rock burst in hard roof mining roadway. The model rationally explains the internal causes of rock burst behavior in hard roof mining roadway. Based on the unloading-slippage model, the principles of influencing factors of rock burst, including the depth, roof strength, roof elastic modulus and roof thickness, coal mass strength and elastic modulus are discussed. Finally, two rock burst events, the 8•2 rock burst in Tangshan coal mine and the 11•11 rock burst in Hongyang mine are analyzed and the unloading-slippage mechanism is the reason in the two events