Deformation, failure, and crack propagation characteristics of fissured red sandstone under uniaxial compression condition.

Fissures are the main controlling factor of rock strength and crack propagation. To study the deformation, failure characteristics, and crack evolution in fissured red sandstone, uniaxial compression experiments were carried out on pre-fissured samples with different dip angles. The acoustic emission (AE) characteristics and complete stress-strain curves were obtained during the experiment, from which several valuable conclusions were drawn. The prefabricated fissures have a significant effect on the peak stress, failure mode, and fissure propagation of the sample under uniaxial compression. As the dip angle (α) increases, the elastic modulus and peak stress show an upward trend, with the elastic modulus rising consistently. Simultaneously, the damage degree decreases. When α > 15°, the peak strain increases with the increase in α. For samples with α < 60°, the stress-strain curve oscillates several times in the yield and post-peak stages, indicating noticeable stress adjustments accompanied by a sharp rise in AE events. In contrast, the curves of samples with α > 60° are relatively smooth. AE events can be divided into three stages: quiet period, stable growth period, and boom period, and the quiet period extends with the increase in dip angle. When α < 45° and equal to 90°, the samples show tensile failure mode, and the rest shows tension-shear composite failure mode.