Characteristics of Ultrasonic Response and Macro-Meso Damage Model During the Loading Process of Single-Fissure Sandstone

The study of the damage mechanics characteristics and failure mechanisms of fractured rock is crucial for evaluating the deterioration process of rock mechanical properties. Focused on single-fissure sandstone, this study conducts triaxial compression tests with real-time ultrasonic monitoring to investigate the relationship between ultrasonic wave propagation patterns and stress evolution in single-fissure rocks. By utilizing ultrasonic wave velocities to establish macroscopic damage variables for fractured rocks and employing the Weibull probability distribution model to define mesoscopic damage variables, a coupled macro-meso damage constitutive model for fractured rock was developed in conjunction with continuum damage theory. The reliability of the model was validated through analysis of experimental data. Results indicate that under triaxial compression conditions, the ultrasonic wave velocity of fractured sandstone exhibits non-monotonic variations with stress. Damage evolution involves an initial weakening followed by a damage accumulation stage. Wave velocity is negatively correlated with damage extent during the damage growth phase and shows a negative correlation with crack width during stress loading. In addition, the failure mode of rock is basically shear failure and tensile-shear mixed failure. The rock crack initiates at the tip of the prefabricated crack and extends to the top, bottom, or side of the specimen at a certain angle with the prefabricated crack. These findings provide significant guidance for understanding the mechanical behavior of fractured sandstone and optimizing mining engineering design.