Numerical Study on The Effects of Inclination and Fracture Length on The Strength and Damage Evolution of Orthogonally Fractured Sandstone

Abstract

Cross fractures are commonly found in natural rock masses and typically exhibit primary and secondary classifications, with their geometric characteristics significantly influencing the stability of rock engineering. This study calibrates the mesoscopic parameters of PFC2D through sandstone laboratory tests and systematically investigates the effects of orthogonal fracture inclination angle and primary and secondary fracture lengths on the mechanical properties and damage evolution of sandstone. The results indicate that the peak stress and peak strain initially decrease and subsequently increase in a concave pattern as the inclination angle rises, reaching a minimum value at an angle of 60°. At an inclination angle of 0°, an increase in the secondary fracture length causes the fracture initiation location to shift from around the orthogonal fractures to the tips of the primary fractures, resulting in a change in the failure mode from diagonal failure to a "figure-eight" shape caused by secondary fracture penetration. When the inclination angle is between 30° and 60°, cracks preferentially initiate at the tips of the primary fractures, and the failure mode gradually transitions from secondary crack propagation to primary crack penetration. At an inclination angle of 90°, cracks at the tips of the secondary fractures initiate first; however, the final failure characteristic exhibits the "figure-eight" shape of primary fracture penetration. Further analysis reveals that the samples mainly experience tensile failure, with cracks propagating from the prefabricated fractures and extending outward in the direction of the principal stress. The findings provide a theoretical basis for the stability assessment of fractured rock masses.