Mechanical properties and energy evolution law of water bearing sandstone under cyclic loading.

Due to excavation disturbances and the coupled hydro-mechanical effects, deep rock masses experience nonlinear large deformations in the surrounding rock, necessitating an urgent exploration of the rock damage and failure mechanisms from the perspectives of hydro-mechanical coupling and mechanical properties. Therefore, this study conducted uniaxial cyclic loading-unloading tests on sandstone samples with different water contents (0%, 0.26%, 0.52%, 0.78%, and 1.04%) to investigate the microstructural evolution, energy evolution laws, and failure characteristics under varying water contents and cyclic loading conditions. The main conclusions are as follows:(1) Concerning micro-pore structures, as the water content increases, the porosity and maximum pore size of the sandstone first decrease and then increase. At 0% water content, the porosity is 4.82% and the maximum pore size is 31.94 µm. At 0.26% water content, both porosity and maximum pore size decrease to 3.03% and 16.15 µm, respectively. When the water content reaches 1.04%, the porosity and maximum pore size increase to 14.34% and 45.99 µm, respectively. (2) Regarding energy evolution laws, the energy evolution of the specimens during cyclic loading-unloading mainly converts to elastic energy, showing a step-wise increase in energy. Further analysis reveals that the water content has a significant impact on the dissipation energy coefficient of the sandstone. At lower stress levels (<0.4σ_max), the water content has a negligible effect, while at higher stress levels (>0.85σ_max), an increase in water content leads to increased fluctuations in the dissipation energy coefficient. (3) In terms of failure characteristics, with increasing water content, the failure mode of the specimens shifts from primary crack failure to microcrack failure, corresponding to the energy evolution during cyclic loading-unloading processes. [ABSTRACT FROM AUTHOR]