The engineering rock masses in high-elevation mountainous regions are generally threatened by freeze–thaw (F-T) weathering, high in-situ stress and dynamic disturbance. It is vital to reveal the dynamic tensile mechanical characteristics and fracture mechanism of rocks subjected to the combined action of F-T treatment and coupled static-dynamic loads. In this study, the coupled static-dynamic loading tests are conducted on F-T treated flattened Brazilian disc (FBD) specimen using a modified SHPB system, and the coupled effect of F-T treatment and pre-tension ratio on the dynamic tensile mechanical properties of sandstone are systematically explored. Moreover, the dynamic fracture features of F-T treated FBD specimens are captured by multiple observation methods, including high-speed photography, digital image correlation (DIC) technique, 3D laser scanning and scanning electron microscope (SEM). The experimental results show that FBD specimens under higher F-T cycles or pre-tension ratios are featured by lower dynamic tensile strength. Besides, with increasing F-T cycles or pre-tension ratios, the fracture surface roughness and the fractal dimension of the fracture surface will decreases, and the microscopic fracture patterns change from brittle to ductile fracture patterns. Moreover, an F-T damage mechanical model is proposed to explain the coupled effects of F-T cycles and pre-tension ratio on macroscopic tensile strength deterioration. The reliability of the mechanical model is verified by comparison with the experimental results. Our results can provide significant guidance for the stability assessment and design of rock engineering in cold regions.
LIU et al. (Tue,) studied this question.