Mechanism and prevention of rock burst caused by the collapse of low level thick hard rock strata at full height mining face in thick coal seam

Based on the basic parameters of coal seam and roof in No. 31103 working face of a mine，combined with the rockburst events occurred in the working face，it is found that the collapse of low level thick hard rock strata is the main reason of rockburst occurred in the mine. Therefore，in order to prevent and control the rockburst induced by the collapse of low level thick hard rock strata，the roof collapse control of No. 31103 working face in the mine was selected as the engineering background. The motion law of the full height roof support layer and follow up layer in the thick coal seam mining was studied by field investigation and theoretical analysis. The mechanical calculation model of the side abutment pressure in the goaf was established，and the mechanism of the rockburst induced by the collapse of low level thick hard strata was revealed. The main results are as follows：① the basic parameters of the low level roof strata of the working face are determined，and the thick cooperative caving strata in the low level strata of the working face are calculated. In the mining process of working face，the follow up layer deforms synchronously with the movement of the support layer，and leads to large energy dynamic phenomenon when the roof of working face falls in large area. ② The mechanical calculation model of side abutment pressure in goaf is established，and the peak position of side abutment pressure in goaf is about 45 m from the edge of goaf，the influence range is about 90 m，and the peak value of side abutment pressure is about 55 MPa. The return roadway of No. 31103 working face is in the influence range of high side abutment pressure in goaf. In the mining process of working face，the stress of surrounding rock in return roadway has reached the stress level of rockburst.③ The mechanism of rockburst in low thick hard rock strata is revealed. The high static load formed by the side abutment pressure in the mining area is the main force source of rockburst，and the disturbance dynamic load caused by the simultaneous collapse of thick hard support layer and its follow up layer is the main inducing force source，and the both superimposed influence causes the rockburst. ④ Targeted prevention and control measures are proposed. Hydraulic fracturing technology and blasting roof cutting technology are used simultaneously in the working face. In the next neibourghing working face，the layout of small coal pillar roadway protection is adopted，and blasting roof cutting is conducted on the goaf side. Based on the above relief pressure measures，the micro seismic events in the continuous mining process of the working face are characterized by frequency reduction，single energy reduction and total energy reduction.