Abstract: The state of tensile-shear stress can easily lead to rock mass damage and even instability. To investigate the tensile-shear failure law of jointed rock mass, numerical simulation of rock mass containing coplanar intermittent cracks under tensile-shear test is carried out through FLAC3D simulation software. For getting high fidelity actual conditions, Mohr-Coulomb constitutive model and maximum tensile stress criterion are amended with rock statistical damage and a function is applied to make the initial mechanical parameters obey the Weibull distribution. Then, failure modes and laws of rock mass are studied under tensile-shear loading. And the influence of homogeneous degree, normal tensile stress and shear rate on rock mass failure modes and processes, as well as its mechanical properties were discussed. The main conclusions can be drawn as follows: (1) Due to the heterogeneous characteristics of natural rock mass, the failure mode is dominated by tensile failure, with little tensile-shear mixed failure. Meanwhile, the initial rupture zones are scattered and then form a strip-shaped fracture surface. The macroscopic mechanical properties of heterogeneous rock mass are obviously weakened than homogeneous rock mass without damage evolution. (2) Heterogeneity has a significant impact on the failure process and strength of jointed rock mass. That is, with the increase of homogeneous degree, the failure mode changes from diffuse type to the concentrated, and the rupture surface roughness increases. The macroscopic strength of jointed rock mass enhances, but there is a ceiling which represents strength of the homogeneous. (3) Under the low stress level, the increase of tensile stress does not change the main rupture mode of rock mass which is tensile failure. However, the proportion of shear and mixed failure are obviously less. Meanwhile, the shear strength of rock mass decreases and the roughness of fracture surface increases. (4) The shear rate has a significant effect on the mechanical properties of rock mass. In the static loading range, the shear strength of rock mass increases with the growth of shearing rate, and the magnitude of the increase is getting smaller.

Key words: statistical damage model, heterogeneity, tensile-shear load, coplanar intermittent crack, rock mass failure