Mechanical, acoustic, and fracture behaviors of yellow sandstone specimens under triaxial monotonic and cyclic loading

The mechanical, acoustic, and fracture behaviors of sandstone play important roles in design and stability analysis in rock engineering applications. In this research, a series of triaxial monotonic and cyclic tests was conducted on yellow sandstone. The results of triaxial monotonic experiments were used to analyze the influence of the confining pressure on the mechanical parameters of the sandstone. The strength and deformation parameters depended strongly on the confining pressure. The triaxial strength of the sandstone specimens under cyclic loading was approximately equal to that under monotonic loading, whereas the fatigue loading led to a reduction in triaxial strength. Under lower deviatoric stress levels, the specimen was highly resistant to fatigue loading; however, higher deviatoric stress level lead to fatigue failure of the specimen even though after large cycle numbers. The influence of the cycle number on the deformation and crack damage parameters of the sandstone was also investigated. The internal damage of the sandstone specimens were characterized on basis of the recorded P-wave velocity and acoustic emission (AE) counts during triaxial monotonic loading, and the effect of the cycle number on the AE behaviors was explored under triaxial cyclic loading. Finally, the fractured yellow sandstone specimens were further analyzed by using X-ray micro computerized tomography (CT) scanning. The internal fracture characteristics of the sandstone specimens were investigated by cross-section analysis and three-dimentional (3D) reconstruction of the CT scanning, which revealed the fracture mechanism of the sandstone.