Stress intensity factors and initiation of unequal collinear cracks in rock

There are many cracks in the natural rock mass and the majority of the cracks are unequal. The main control crack with a certain scale decides the stability of the rock mass. In order to study the interaction rules of the cracks with unequal length and the initiation rules of the main control crack, based on the Kachanov method, the expressions for the stress intensity factors of two collinear cracks with unequal length loaded by uniaxial tractions at infinity are derived, and the influence of the crack distance on the interaction is theoretically analyzed. The initiation angle of the main crack under uniaxial tension is calculated by the maximum circumferential stress criteria and the theoretical fracture criteria curves are drawn. The stress intensity factors of sliding close cracks are derived and the compression tests on rock-like specimens with two unequal collinear cracks are performed. The results show that the small crack almost has no effect on the initiation of the main control crack when the crack distance reaches the length of the small crack. The initiation angle of the main control crack is only related to the crack incline angle, and it decreases with the increase of the crack angle when the cracks are loaded by uniaxial tension and it increases with the increase of the crack angle when the cracks are loaded by uniaxial compression. The initial critical load increases rapidly when the crack incline angle is less than 30°.