Influence of crack aperture and orientation on the uniaxial compressive behavior of rock

The pre-existing cracks with various geometric and physical properties significantly affect the mechanical behaviors of rock mass. In this study, uniaxial compressive tests are performed on numerical models of specimens containing a single pre-existing crack with different apertures and orientations based on PFC 2D to shed light on the impact of different crack apertures and orientations. The results reveal that the uniaxial peak strength and elastic modulus tend to decrease with increasing apertures, but they tend to increase with increasing inclination angles. Crack apertures can affect the stress intensity factor in the vicinity of the pre-existing crack tips, which further influences the crack initiation and crack type. Furthermore, shear cracks are more prone to occur in a pre-cracked specimen with a larger crack aperture and larger crack orientation. The crack initiation stress and strain initially show a slight decrease until the inclination angle reaches 45°, and then significantly increase with the further increase of angle from 45° to 90°. The microcracks occur earlier and easier when the inclination angle is 45°. As the inclination angle of the pre-existing crack increases, shear-sliding along the crack becomes more prominent, resulting in the formation of coplanar secondary cracks. The macro failure patterns switch from tensile failure to shear failure with increasing crack inclination angle, which is in good agreement with trend lines of displacement in the displacement field.