Effect of layered joints on rockburst in deep tunnels

Abstract

The existence of joints in the surrounding rock mass has a considerable effect on tunnel rockbursts. Herein, we studied the effect of layered joints with different inclination angles and spacings on rockburst in deep tunnels and investigated the failure area, deformation process of the surrounding rock mass, stress change inside the surrounding rock mass, velocity of the failed rock, and the kinetic energy of the failure. The failure type of the surrounding rock mass can thus be determined. The results showed that the intensity of rockburst increases as rock quality designation (RQD) decreases, while the deformation rate of the surrounding rock mass first increases and then decreases. The deformation rate exhibits a turning point between RQD = 50 and 70, below which the deformation rate of the surrounding rock mass gradually decreases, ultimately ceasing to be a rockburst. Rockburst always occurs perpendicular to the direction of the joint. When σx = σy, as the joint inclination angle changes from 45° to 90°, the intensity of a rockburst first decreases (from 45° to 60°), and then increases (from 60° to 90°). When combined with the evolution law of stress and strain energy, the rockburst process can be divided into four stages.