Mechanical properties and crack propagation behavior of flawed red sandstone coated with a thin spray-on liner material under uniaxial compression

Taking red sandstone as the research object, intact and flawed red sandstone specimens coated with liner were made using a cement-based thin spray-on liner (TSL). This study investigated the effects of the TSL on the strength, deformation, and energy evolution of intact and flawed red sandstone under uniaxial compression. Furthermore, the crack propagation characteristics of TSL-coated sandstone with different inclination angles were analyzed through particle flow PFC^3D software. The results indicate that the peak strength and strain of red sandstone coated with the TSL were greater than those of the uncoated specimens. Moreover, the improvement coefficient for flawed sandstone exceeded that of intact specimens. In the post-peak stage, the internal rock of specimens coated with the TSL was damaged, resulting in the formation of tensile cracks on the liner surface, although the specimens did not fully collapse. The total energy, elastic energy, and dissipated energy of specimens with a TSL are greater than those of the uncoated specimens. Moreover, a greater amount of input total energy is converted into dissipated energy after coating. The PFC^3D simulation results indicate that applying the TSL can increase the initiation stress and peak strength of crack specimens at different inclination angles. Influence of the TSL on the failure modes of specimens with varying crack angles. Specifically, at a 15º inclination angle, the thin spray-on liner hinders the propagation of tensile cracks in the post-peak stage. Conversely, at a 75º inclination angle, the crack propagation behavior of the specimens, whether coated or uncoated with the TSL, is similar. These research findings can provide a reference for the application of TSLs in engineering applications.