Numerical study on rockburst induced by spalling-structural buckling in surrounding rock with vertically parallel joints of deep hard-brittle large-section square tunnel under cyclic loading-unloading

Aiming at the engineering problem that spalling-structural buckling rockburst is easily induced in vertical parallel-jointed surrounding rocks of deep hard-brittle large-cross-section square tunnels under cyclic loading-unloading, a 100 m × 100 m two-dimensional numerical model was established using the cyclic loading version of RFPA 2D software. The whole process of rockburst evolution of surrounding rocks under 70∼130 MPa cyclic loading was simulated, the mechanical response laws under cyclic loading were explored, and the evolution mechanism of spalling propagation and structural buckling was revealed. The results show that the failure of surrounding rocks follows the progressive law of stress concentration → directional splitting → slab formation → buckling instability. The acoustic emission (AE) damage count presents a nonlinear evolution characteristic of slow increase in the early stage and rapid surge in the later stage, with the 22nd cycle as the mutation point of rockburst, and the cumulative AE damage count increases exponentially. The axial unloading deformation, axial elastic deformation, axial residual deformation and axial loading deformation are significantly positively linearly correlated, and the linear accumulation of residual deformation reflects the continuous superposition of fatigue damage in surrounding rocks. The element stress and displacement of surrounding rock both show a cumulative increasing trend with the rise of cycle number. The stress concentration and displacement mutation can be taken as important precursors for predicting spalling-structural buckling rockburst. Innovatively focusing on the coupling characteristics of vertically parallel joints and large-cross-section square tunnels, this study clarifies the evolution mechanism of spalling-structural buckling rockburst under cyclic loading-unloading, and proposes the prediction indicators of rockburst based on AE signals and deformation parameters. The research results can provide a theoretical reference for rockburst prediction and prevention-control design of jointed surrounding rocks in deep large-cross-section square tunnels.