Unloading-slippage mechanism of coal bump in gateroad of longwall

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.