EVOLUTION LAW AND MECHANISM OF ROCKBURSTS IN DEEP TUNNELS: IMMEDIATE ROCKBURST

The ideas and methodology for the in situ monitoring of rockburst preparation of deep tunnels was described firstly.The time and space evolution law of immediate rockburst observed,which occurred usually during or after excavation immediately and affected mainly by excavation unloading effectiveness,was analyzed.Based on a series of in situ monitoring of deep tunnels,process of crack initiation,propagation,opening and closing,evolution of wave velocity,deformation,acoustic emission and microseismicity were observed.Based on moment tensor analysis of the monitored microseismicity during the excavation of deep tunnels,the difference of mechanism of strain rockburst and strain-structure slip rockburst was found.The former was mainly from tensile cracking but the latter mainly from tensile cracking,shear cracking,and tensile-shear/compressive shear cracking which was from shearing of stiff structures and formed boundary of rockburst pit.The results are used as a guide of prediction of rockburst and its dynamic control based on evolution of the monitored microseismicity and other information.