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.