Effect of Crack Angle on Mechanical Behaviors and Damage Evolution Characteristics of Sandstone Under Uniaxial Compression

Hydraulic fracturing has been extensively utilized to control strata in coal mines. However, the mechanical characteristics and damage evolution of the fracturing rock mass have not been thoroughly explored. In this study, the effects of fracture dip angle on sandstone mechanical properties, failure modes, energy characteristics, and damage progression were investigated through uniaxial compression and acoustic emission monitoring systems. The results indicate that with the increase in the fracture angle, the compressive strength and elastic modulus of sandstone display an asymmetrical "U"-shaped change trend, and the failure mode of the sample is a mixed tension-shear failure. Throughout the loading process, the acoustic emission ringing counts and energy signals were imperceptible in the early stages, but rapidly increased to the peak value as the sample approached failure. Moreover, the acoustic emission amplitude signal showed the phase characteristic of active-calm-reactive to the peak point. With the increase in fracture inclination, the total strain energy and elastic energy at the peak point of sandstone also show an asymmetric "U"-shaped change trend. The energy storage capacity, dissipation capacity, and energy release intensity of the rock were characterized using a quadratic function relationship with the crack angle, theta, indicating that the difficulty of rock failure driven by energy follows a difficult-easy-difficult trend. In addition, a coupling damage model considering macro cracks and micro defects was established, demonstrating that the theoretical results are in good agreement with the experimental results.