Study on Deformation and Energy Characteristics of Sandstone under Multistage Cyclic Load in Complex Stress Environments

To investigate the effects of multistage cyclic loading on sandstone under complex stress environments, uniaxial cyclic compression tests were conducted under different prestress conditions, incorporating acoustic emission (AE) monitoring and energy analysis. The results show that low-prestress loading has more pronounced strengthening effects on sandstone, while high prestress produces the opposite trend; increasing prestress leads to significantly higher AE counts and more severe specimen failure. Energy analysis reveals that low-prestress samples require about 9% more energy to fail compared to high-prestress conditions. Under high prestress, sandstone exhibits reduced elastic deformation and lower energy storage capacity (with storage coefficients consistently below 90% when stress lower limits approach zero), along with notably increased plastic deformation and energy dissipation. This study clarifies the damage and energy evolution mechanisms of sandstone under cyclic loading.