Quantitative mechanism of roadway rockbursts in deep extra-thick coal seams: Theory and case histories

•Critical indexes of roadway rockburst initiation and their formulas were proposed.•Controlling factors of roadway fracture occurrence and rockburst were clarified.•Quantitative description of rockburst induced by mine seismicity was achieved. Rockbursts are globally recognized as one of most severe dynamic disasters in mines. Generally, rockbursts can be divided into self-initiated bursts type and remotely triggered bursts type in terms of their occurrence mechanism. In recent years, various remotely triggered roadway rockburst accidents (induced by seismic disturbance) in deep extra-thick coal seam have been reported in China. In this study, using stability theory, seismic disturbance factor was involved with in-situ stress, mechanical properties of the coal and rock mass, support strength, and roadway size to establish a mechanical model for rockburst and to obtain critical indexes of the surrounding rock fracture and rockburst occurrence. Accordingly we achieved the quantitative description of a remotely triggered roadway rockburst in extra-thick coal seams. In detail, using a rock fracture criterion, the critical ground stress indexes and corresponding formulas of surrounding rock softening and fracture occurrence were determined. Moreover, using an instability criterion, critical indexes of the roadway rockburst initiation were established, including the critical radius of the fracture zone, the critical radius of the softening zone, critical stress, maximum allowable disturbance stress, magnitude, and energy. The main influencing factors and laws of rockbursts were determined quantitatively. The critical indexes were quantitatively calculated using some typical case histories of roadway rockbursts in coal mines in China, which would lay a foundation for the development of quantitative criterion of rockbursts.