Experimental investigation on the correlation between fracture surface characteristic and in situ stress of different depths rock based on wave velocity method

Wave velocity is closely related to the transverse propagation direction of rock fracture surfaces. In this study, the directions of the principal stress and principal strain in different height planes of the samples were determined by circumferential ultrasonic measurements. Considering the relationship among the directions of the principal strain, transverse propagation, and in situ stress release, the mechanism of transverse fracture propagation driven by micro-cracks caused by in situ stress is explained. The effects of the confining pressure, initial rock damage, and circumferential wave velocity anisotropy on the incline angle were analysed. The results indicate that the directions of the principal stress and principal strain were approximately perpendicular to the central position of the samples. Significant deflection occurred in the principal stress direction at the top and bottom. The fracture surface transverse propagation direction was close to the principal strain direction at the central position, and the incline angle decreased with increasing confining pressure. The influence of the micro-crack volume proportion on the angle decreased with an increase in the initial damage. In addition, the incline angle and initial damage first decreased and then increased with the fractal dimension. Under different fractal dimensions, the change trend of the lower envelope incline angle exhibited a negative exponential relationship with the confining pressure. The fractal dimension decreased exponentially related to the chlorite content. This study provides a theoretical guidance for predicting failure locations in rock engineering.