Experimental study on the fracture and fatigue behaviors of flawed sandstone under coupled freeze-thaw and cyclic loads

This paper investigates the effects of coupled freeze-thaw (FT) cycles and cyclic loads on the mechanical properties, cracking behaviors and fatigue damage mechanism of flawed rocks. The digital image correlation technology is used to monitor the real-time cracking process and to analyze the evolution characteristics of deformation fields for tested samples. The effects of FT cycles and ligament angles on the mechanical evolution properties of flawed rocks subjected to cyclic loads are first analyzed. Secondly, the cracking processes of flawed rocks with different ligament angles subjected to FT cycles are studied in detail. Seven types of cracks including anti-wing crack, wing crack, oblique secondary crack, far-field crack, out-of-plane shear crack, out-of-plane tensile crack and quasi-coplanar secondary crack are observed. Two crack initiation modes including wing crack initiation and anti-wing crack initiation are registered, and seven crack coalescence types in tested samples are discriminated. The apparent displacement fields can be employed to reveal the fracture mechanism of flawed rocks under coupled FT cycles and cyclic loads. Finally, the fatigue damage mechanism of FT cycles coupling with cyclic loading and unloading is discussed in detail. The experimental results are very meaningful to evaluate the safety and stability of rock engineering in cold regions.