Abstract: The study of crack initiation, propagation, and connection mechanisms has important implications for the stability and safety of rock mass engineering. The Mohr-Coulomb criterion is first introduced into the classical phase field model, and a mixed crack driving force composed of pure tension, tension-shear, and compression-shear is established. Based on the Benzeggagh-Kenane fracture criterion, the equivalent I-II mixed-mode critical energy release rate is obtained to replace the mode-I critical energy release rate in the classical phase field model, and a modified phase field model is proposed to simulate the mixed-mode fracture of rock masses. In addition, a discrimination criterion is proposed based on the modified phase field model, which includes tensile crack, shear crack, and mixed tensile-shear crack. Finally, the uniaxial compression test of fissured specimens with different geometric defects is simulated and compared with experimental and numerical results, demonstrating that the proposed modified phase field model not only has the ability to simulate mixed fracture of fissured rock masses, but also can distinguish crack modes. The research results contribute to improving the understanding of the fracture mechanism of fissured rock masses.

Key words: phase field model, rock mass, crack propagation, crack mode