Failure mechanism and energy evolution of deep hard rock subjected to true triaxial unloading under different initial...

Research on the deformation and failure mechanism of deep hard rock is of great significance for the prevention and control of rockburst in high-stress underground engineering. In this study, true triaxial single-face unloading rockburst tests were conducted on Jinchang diorite under different initial stress differences. The effect of initial stress difference on strength response, failure behavior, and energy evolution mechanism of diorite was investigated using scanning electron microscopy (SEM) and acoustic emission (AE) monitoring, and the fractal dimension of rockburst fragments and rockburst proneness were quantitatively discussed. The results demonstrated that the peak strength increases significantly with increasing initial stress difference, and the macroscopic failure pattern evolves from randomly distributed tensile-shear coupled cracking to localized tensile slabbing along the unloading free surface. The fracture surface morphology changes from rough surfaces with irregular step-like tearing features to smooth cleavage planes with river-like patterns, and AE activity changes from gradual cluster-type signals to sudden main-shock-type release. In addition, a true triaxial discrete element numerical model based on PFC3D was established and calibrated to investigate the microcrack evolution and orientation under different initial stress differences, and the numerical results were in good agreement with the experimental observations.