Effects of crack inclination and aperture on mechanical properties and fracture behavior of sandstone: an experimental study based on acoustic emission monitoring

The inclination and aperture of rock fractures significantly influence the mechanical properties and crack propagation behavior of rock masses. To investigate the deformation characteristics and crack evolution in sandstone, uniaxial compression tests were conducted on specimens containing pre-existing cracks with different apertures (1 mm, 3 mm, and 6 mm) and inclination angles (0°, 30°, 45°, 75°, and 90°). Acoustic emission (AE) monitoring was employed to capture the mechanical response and crack development in real time. The experimental results indicate that the peak strength decreases significantly with increasing crack aperture, while it increases with larger inclination angles. The stress-strain curves can be divided into four distinct stages: initial compaction of pores and micro-cracks, linear elastic deformation, stable crack propagation, and post-peak failure. The failure mode transitions from shear-dominated to tensile-dominated fracture as the inclination angle increases. Based on the crack initiation stress criterion, the crack initiation stress increases with higher inclination angles due to the enhanced restraining effect of the maximum horizontal principal stress on crack opening. In contrast, the crack initiation stress decreases with larger apertures, which is attributed to the greater proportion of initial defects and their significant influence on stress distribution and crack propagation patterns. These findings provide valuable insight into the mechanical behavior and failure mechanisms of fractured sandstone.