Crack Initiation and Propagation Mechanism of Flawed Rock Mass Based on Improved Maximum Distortion Energy Theory and PFC Numerical Simulation

In order to explore the crack initiation and propagation evolution characteristics of flaw rock masses, the crack initiation mechanism of rock masses based on improved maximum distortion energy theory was analyzed. The relationship between the flaw inclination angle, initiation angle, and Poisson's ratio of single-flawed rock was revealed. Based on the Particle Flow Code PFC2D embedded in the "FISH" language, discrete element simulations were conducted on rock specimens with a pre-existing single-flawed under uniaxial compression. The crack initiation angle, stress characteristics, acoustic emission characteristics, and the evolution law of crack propagation for rock specimens with different flaw inclination angles were investigated. Numerical simulation results indicate that under uniaxial compression, as the flaw inclination angle increases, the peak stress of the rock continuously decreases, the crack initiation angle and rock propagation stress increase, while the initiation stress of rock initially decreases and then increases. The cracks were initiated at the tip of the pre-existing flaw and propagated by shear stress along the pre-existing flaw direction, ultimately resulting in diagonal shear failure. The improved maximum distortion energy theory calculations show that under uniaxial compression, for composite-type cracks, an increase in Poisson's ratio causes the sensitivity of the initiation angle to the flaw inclination angle to continuously increase. The increase in the flaw inclination angle enhances the influence of Poisson's ratio on the initiation angle. This study provides theoretical references for the crack initiation mechanism of natural flaws in underground engineering rock masses, the failure modes of surrounding rock, and stability control.