Influence of fissure angle and loading rate on sandstone failure mechanisms: implications for underground engineering stability

Abstract This study investigated the influence of fissure angle and loading rate on the stability of flawed rock masses. Uniaxial compression tests were conducted on sandstone specimens containing a single hole and double fissures, monitored simultaneously by acoustic emission (AE) and digital image correlation (DIC). The coupled effects of fissure inclination (0°–90°) and loading rate (0.05–0.20 MPa/s) were systematically analyzed. Results demonstrate that both peak strength and peak strain increased significantly with fissure inclination angle, accompanied by enhanced AE activity. DIC strain field evolution revealed that crack initiation occurred at fissure tips. These cracks subsequently interacted with the hole, forming stress concentration zones that ultimately led to specimen instability. Specimens with 0° and 45° fissures exhibited shear failure, while those with 90° fissures failed through axial splitting. Based on strain field characteristics, three pure crack types and eight mixed crack types were identified and classified. These findings provide critical parameters and criteria for assessing rock mass stability and optimizing support designs in underground engineering projects, including tunnels, slopes, and chambers under Mining Disturbance. This research offers practical guidance for ensuring engineering safety throughout project lifecycles.