Investigating the Influence of Joint Angles on Rock Mechanical Behavior of Rock Mass Using Two-Dimensional and Three-Dimensional Numerical Models

Numerical testing is an ideal testing method in the research on the mechanical behaviors of jointed rock. However, there are few systematic studies focused on the comparison between the two-dimensional (2D) and the three-dimensional (3D) simulation effects on rock mechanical behaviors, particularly those of jointed rock. In this paper, a particle flow model was established by utilizing PFC2D and PFC3D to represent the rock materials, and the rock (especially jointed rock) mechanical behaviors (uniaxial compressive strength UCS, tensile strength TS, crack initiation stress level K-sigma, and the pattern of crack initiation) between 2D and 3D models were compared and analyzed. As expected, the result shows that the UCS and TS showed an increasing tendency with the increase in the joint angle (beta) for both the 2D and the 3D models, and the strength of the 3D model was less than that of the 2D model under uniaxial compression but was greater than that of the 2D model under uniaxial tension. The crack initiation and K-sigma of the specimens were essentially the same for the 2D and 3D models, and the tensile stresses are more concentrated than the compressive stresses before the failure of the specimen; the uniaxial tensile failure more closely approached abrupt failure than the uniaxial compression failure. The tensile cracks were often initiated at the tips of the joints for both the 2D and 3D models, but they were initiated in the middle of the joints when beta was low (beta = 0 degrees and beta= 15 degrees in both the 2D and 3D models) under uniaxial compression and when beta reached 90 degrees under uniaxial tensile. The test results were validated and further analyzed with mathematical analysis. This study has relative referential value to experiments on jointed rock and to analysis of the instability fractures of engineering rock mass.