Dynamic response and rockburst characteristics of underground cavern with unexposed joint

Abstract

The existence of joints poses a challenge to the dynamic stability of underground caverns. To investigate the dynamic response of the underground cavern affected by an unexposed joint, a series of SHPB tests were conducted on the marble specimens with a cavern and differently distributed joint, including the cases of joint location dips of 0°, 56°, 90°, 134°, and 180° and the case of no joint. The discrete element method was also adopted to uncover the dynamic failure mechanism of samples. Based on the experimental and numerical results, the effects of joint distribution on the fracturing process, dynamic strength and local stress evolution of underground caverns were systematically investigated. The deformation characteristics, failure patterns, rockburst characteristics and rockburst mechanism were identified for different joint cases. The results showed that the joint has limited influence on the dynamic bearing capacity and failure characteristics of the cavern when the dip θ = 0°, 90° and 180°, but it becomes significant when the dip θ = 56° and 134°. Similarly, when the dip θ falls in the range of 56°∼134°, the maximum principal stress around the cavern will be significantly affected, but not when the dip θ is 0° or 180°. More specifically, different joint distributions can cause four kinds of rockbursts on the cavern: A) strain rockburst at the roof; B) strain rockburst at the floor; C) slip rockburst of wing cracks at the roof; and D) slip rockburst of wing cracks at the floor. When these rockbursts occur, the displacements of surrounding rocks will demonstrate obvious abnormal changes (e.g., characteristic oscillations and sudden changes), and C-type rockbursts generally lag behind A-type rockbursts. In addition, the magnitudes of the strain energy release rate can be identified: D-type rockburst > A-type rockburst > B-type rockburst > C-type rockburst > no rockburst. The findings of this study will benefit the stability analysis and risk control of underground caverns.