Mechanical Degradation and Acoustic Emission Characteristics of Sandstone Containing Intersecting Fissures Under Uniaxial Compression

Intersecting fissures strongly affect stress transfer and crack coalescence in rock, but their coupled effects on mechanical degradation and acoustic emission signatures remain incompletely understood. We conducted uniaxial compression tests with synchronous acoustic emission monitoring on prismatic sandstone specimens containing five intersecting-fissure configurations and on intact controls. The specimens measured 50 mm × 50 mm × 100 mm, and each prefabricated fissure was 30 mm long and 2 mm wide. The central 0–90° configuration produced the greatest degradation: its peak stress, peak strain, and elastic modulus were about 70%, 36%, and 50% lower, respectively, than those of the intact specimen. Acoustic emission ring-down counts captured the transition from early crack activation to unstable coalescence and increased sharply near macroscopic failure. Low-inclination configurations generated predominantly intermediate- and high-frequency signals, consistent with the activation of numerous small tensile cracks. Gaussian mixture model clustering of rise angle and average frequency values further showed that tensile microcracking dominated all fissured specimens, whereas the shear-crack fraction increased with fissure angle α. These findings link fissure geometry, macroscopic weakening, and acoustic emission source characteristics under uniaxial loading, providing a laboratory basis for identifying potentially hazardous intersecting-fissure configurations in underground rock engineering.