Fatigue behaviors of pre-flawed orthoclase granite under monotonic and multi-level cyclic loadings

Fissures with various inclination angles are present in engineering rocky slopes, a structural geological product, profoundly influence the long-term stability of rock engineering; whereas, exploration on its macroscopic failure mechanisms and fatigue mechanical characteristics of pre-flawed granite specimens are insufficient. Therefore, this study investigated the fatigue mechanical responses and meso-macro fracture mechanisms of pre-flawed granites with different pre-flaw spaces under monotonic and multilevel fatigue loadings using the CT imaging and three-dimensional crack reconstruction technology. Results showed that the strength of granites with short, medium and long flaw-spacing and intact specimens increased sequentially. Under multilevel fatigue loading, the stiffness of pre-flawed granite produced a significant hardening and a staged increase, similar variation pattern was also reflected by the input energy density and elastic strain energy. Meanwhile, In the last fatigue stage, the damage factor of granites appeared a ‘$\left(\underline{}\right)$’ − shaped upward trend, the damage deterioration rate of the specimens was the fastest during this stage. Finally, the type of pre-flaw spacing controlled the macroscopic failure patterns and crack network of granite. The non-uniform stresses at tips of pre-flawed flaws were responsible for inhibiting cracks development. The smaller the non-uniform stress was, crack network had the more possible properties to develop. Consequently, the crack network was more developed in granite with longer pre-flaw spacing.