Mechanism and monitoring and early warning technology of rock burst in the heading face of compound thick coal seam

For the characteristics of frequent ejection of coal particles,long duration of vibration,and concentrated im- pact damage range near the heading during the excavation of the compound thick coal seam face in the western mining area of China,taking the compound thick coal seam heading face in Liuhuanggou coal mine as an engineering back-ground,the mechanism of coal pellet ejection and rock burst and the monitoring and early warning technology in the heading face at compound thick coal seams were studied using field investigation,theoretical analysis and on-site moni- toring methods. The results show that the soft coal part of the surrounding rock will quickly unload and destroy the coal particle ejection after the roadway is excavated,and the soft coal damage will cause local hard coal shear stress con- centration. When the degree of stress concentration exceeds the ultimate strength of hard coal,the shear failure of hard coal occurs,which in turn induces head-on rock burst. The on-site monitoring results show that there is no obvious sign of coal body stress and anchor cable pressure monitoring before and after rock burst in the heading face of compound thick coal seams. Acoustic emission monitoring can capture the information of rock burst,but many small energy vibra- tion events caused by frequent coal burst seriously affect the accuracy of the monitoring and early warning results. Therefore,this paper propose a monitoring and early warning method based on the concept of “high energy acoustic e- mission events”,that is,only the high-energy acoustic emission events that have a significant impact on the rock burst of the heading face are monitored. These acoustic emission events have the obvious feature that the total frequency of occurrence is relatively low,but the total energy is high. According to statistical analysis,the acoustic emission in the working face of (4-5)04 headgate with the energy greater than 1 000 mV is called the high energy acoustic emission events. Compared with the original early-warning methods,the early-warning methods based on the concept of “ high energy acoustic emission events” have a higher accuracy and more in line with the actual situation on site.