Study on acoustic emission response and damage evolution characteristics of sandstone with X-shaped fissures at different inclination angles under uniaxial compression

Uniaxial compression and acoustic emission (AE) tests were conducted on sandstone containing X-shaped fissures with different intersection angles to investigate the regulatory effect of fissure intersection angle on the failure process of sandstone. The results indicate that the intersection angle significantly controls the AE response and damage evolution characteristics. At α = 60°, high-frequency signals (280–330 kHz) are the most sparse, AE activity is the lowest, and the resistance to deformation is the weakest. In contrast, α = 30° and 90° exhibit more intense high-frequency AE activity, reflecting a more vigorous crack evolution process. RA–AF analysis indicates that tensile failure dominates under all working conditions (82.5–92.4%), exhibiting a tensile–shear mixed failure mode. Moreover, the proportion of tensile cracks shows a trend of first decreasing and then increasing with the variation of the intersection angle, which is consistent with the strength evolution law. The cumulative ringing count response exhibits a three-stage characteristic of “quiescent–stable–abrupt.” The inflection point appears earliest at α = 60° and 75° (approximately 165 s), indicating that these specimens enter the plastic evolution stage earlier. The fitting results based on the S-shaped damage model (R² > 95) further indicate that α = 60° corresponds to the earliest onset of damage acceleration, while α = 75° exhibits the highest damage evolution rate (B = 0.17). The study reveals the intrinsic mechanism by which the fissure intersection angle governs the failure process of sandstone by regulating crack propagation paths and the rate of damage accumulation.