Mechanical behavior of rock-like samples with preexisting flaws: Influence of crack geometry on crack evolution and stress distribution

Underground engineering plays an important role in modern urban construction, transportation infrastructure, and resource extraction. The influence of the geometric characteristics of cracks in rock masses on their mechanical behavior and failure modes is a key scientific issue for ensuring the safety of underground structures. This study systematically investigates the effects of prefabricated crack angle and length on the mechanical response, crack propagation, and stress distribution of rock-like samples through uniaxial compression tests and particle flow code in two dimension (PFC2D) numerical simulations. The results show that crack angle significantly affects the sample strength, exhibiting a nonlinear trend of initially weakening and then strengthening. Increasing crack length exacerbates stress concentration, leading to a gradual reduction in peak strength and ultimately to saturation. Crack angle and length jointly influence the crack propagation path and failure mode. As the crack angle increases, the failure region shifts from the sample edge to the center. Longer cracks enhance the dominance of crack-induced failure and reduce the influence of preexisting holes. When the crack angle approaches 45°, acoustic emission (AE) energy release becomes more concentrated and abrupt. Moreover, longer cracks lead to earlier AE onset and faster energy accumulation. At the high-stress stage, the influence of crack geometry on stress distribution becomes more pronounced. The highest stress concentration occurs at a crack angle of 22.5°, and increasing crack length results in more complex damage evolution. Numerical simulations further validate these findings, revealing that both crack angle and length play dominant roles in stress redistribution.