Coupled mechanism of compression and prying-induced rock burst in steeply inclined coal seams and principles for its prevention

Abstract

Rock bursts frequently occur in steeply inclined and extremely thick coal seams (SIETCS), posing severe challenges to safe mining. To reduce the risk of rock burst in SIETCS, this study investigated the mechanisms of the rock bursts occurrence in SIETCS and formulated the principles for its prevention. To this end, field investigation, geophysical monitoring, theoretical analyses, and numerical simulation were employed. Mechanical models have been developed for a “steeply inclined suspended roof structure” and a “steeply inclined suspended rock pillar structure”, which are relevant to the rock burst mechanisms. The elastic deformation energy distribution functions for both models have been obtained, and the factors influencing the elastic deformation energy have been analyzed. The sources of microseismic (MS) events associated with rock bursts monitored in the typical SIETCS (with a dip angle of 87°) are mainly concentrated in the roof and interlayer rock pillar, making up 17.0% and 60% of the events recorded, respectively. The elastic deformation energy of the roof and rock pillar is mainly influenced by the dip angle of the coal seam, the lateral pressure coefficient, and the supporting force coefficient. The peak stress of the coal body at the compressive and prying area is 1.7 times of the horizontal tectonic stress. The minimum normal and tangential dynamic load stresses generated by the recorded rock bursts are 84.5 MPa and 48.6 MPa, respectively; such stress levels exert strong destructive forces when superimposed with static stress. The analytical results of the failure law of rock burst, MS monitoring, mechanical model, numerical simulation, and elastic deformation energy function of the typical SIETCS identify the main causes of rock burst as the high static stress of a coal body under the coupled action of compressive and prying effects of roof and rock pillar and the dynamic stress caused by breakage of the roof and rock pillar. The damage models and the damage process by which a rock burst is induced have been constructed. Three mechanisms by which a rock burst can occur in SIETCS are proposed. Finally, prevention principles of load-reduction and prying-reduction for rock burst in SIETCS have been developed.