Effect of stress amplitude on mechanical and acoustic emission of sandstone under constant–cyclic loading

The mechanical characteristics of sandstone under constant–cyclic loading with different amplitudes play a significant role in geotechnical engineering. In this research, constant–cyclic tests with stress amplitudes of 5%, 10%, and 15% of the uniaxial compressive strength were conducted to analyse the effect of stress amplitude on the mechanical behaviours of sandstone. Then, the internal crack propagation of sandstone was characterized based on the real-time record of an acoustic emission (AE) technique. Finally, the fragments of the rock mass distribution and failure pattern were assessed. The results showed that the cyclic deformation, acoustic emission response, fragmentation characteristics, and internal cracks depend strongly on the stress amplitude. With increasing stress amplitude, the peak strength first increases and then decreases. There may exist a specific loading amplitude that increases the peak strength. In addition, a higher stress amplitude may lead to peak strength degradation to some extent. In addition, the elastic and dissipated energy shows decreasing and increasing trends in the cyclic loading stages, respectively. Elastic energy accounts for the largest proportion of all input energy. The fragment distribution is more uneven, the percentage of large and small blocks increases, and the failure patterns are more complex under higher stress amplitudes, which can reveal the fracture characteristics of the sandstone under different amplitudes. These results can offer a reference to understand the different disruption effects on the engineering characteristics of sandstone and play a guiding role in the mining-induced stress boundary movement and control of dynamic disasters.