NUMERICAL STUDY ON TENSION-SHEAR FAILURE MECHANISM OF HETEROGENEOUS COPLANAR INTERMITTENT JOINTED ROCK MASS

The rock mass in the unloading disturbance zone near the excavation face of project is affected by the structural plane and tensile stress. Deformation and failure of the rock mass are characterized by the loading combining tension and shear. However, previous studies have focused on the tensile failure and compression-shear composite failure of intact rock or rock mass. The deformation and failure behavior of rock mass under tensile and shear stress conditions was less involved. This paper aims to study the mechanical behavior of jointed rock mass under combined tension and shear condition. A series of numerical simulation studies on coplanar discontinuous jointed rock mass are carried out using particle discrete element method. It assumes that the micro mechanical parameters of the intergranular contact obey the Weibull distribution to characterize the heterogeneity of the rock mass. The influence of the heterogeneity, homogeneity, normal tensile stress and joint connectivity rate on the tensile strength and failure mode of the jointed rock mass is discussed. The research results indicate that the heterogeneous jointed rock mass is primarily destroyed along the stepped fracture surface under the condition of combined tension and shear stress. The shear stress-horizontal displacement curve can be divided into the linear deformation stage, the nonlinear deformation stage, the peak and the post-peak stage. With the increase of homogeneity degree, the shear strength of jointed rock mass increases gradually and the lifting amplitude decreases gradually, which tends to be the same as that of homogeneous rock mass and the degree of breakage of the fracture surface is reduced. The micro-cracks in the rock mass are concentrated from the diffuse distribution to the fracture surface. Peak shear strength of jointed rock mass and the magnitude of the normal tensile stress are nonlinearly and negatively correlated. With the increase of the normal tensile stress, the failure mode of the jointed rock mass is transformed from tension-shear mixed type to tension type, and the roughness of the fracture surface is increased to varying degrees. The shear strength of jointed rock mass decreases significantly with the increase of joint connectivity rate.