Study on Acoustic Emission and Crack Propagation Characteristics of Single-Fissured Sandstone with Different Angles Under Uniaxial Compression

The uniaxial compression tests are conducted on single-fissured sandstone with different angles, and the effect of fissure angle (β) on mechanical properties, acoustic emission (AE) features, crack propagation characteristics, and failure mode of sandstone are studied with the AE monitoring and photographic system. The research results reveal that as the β increases, the uniaxial compressive strength (UCS) exhibits an asymmetric inverted “U” shape and the minimum is only 33.14 MPa when β = 30°, while the elastic modulus increases monotonously from 8.98 to 15.14 GPa. During the loading process, the AE parameters demonstrate obvious stage characteristics, while tension cracks dominate and the shear cracks significantly increase. As β increases, the AE activity gradually shifts to the post-peak destruction stage, and the effect of shear crack on the final failure mode of the specimens becomes more significant. The stress–strain relationship, AE features, and real-time photographic system are sufficient to comprehensively depict the crack evolution process in each stage, and there is a good correlation between each parameter. Increase in β makes the crack initiation stress and its ratio to UCS increase, from 68.74% to 79.92%, which makes it more difficult for crack initiation, and the secondary crack propagation gradually transforms from tension to shear. The macroscopic failure mode of fissured sandstone gradually changes from tension failure to mixed tension–shear failure and finally to shear failure, the angle between the propagation direction of initial cracks and fissure gradually decreases, and the surface spalling zone becomes more obvious.