Damage Analysis of High-Frequency Disturbance in Sandstone Creep Process Based on NMR Technology

The creep characteristics of sandstone under high-frequency disturbance were investigated. Nuclear magnetic resonance (NMR) technology was used to investigate the characteristics of pore changes in sandstone before and after disturbance creep. Quantitative analysis was conducted on the transverse relaxation time (T-2) distribution, changes in porosity, and percentage changes in macropores (T-2 > 10 ms) and micropores (T-2 < 10 ms). Moreover, the variation characteristics of creep strain before and after disturbance creep, as well as the corresponding changes in steady-state creep strain and the creep strain rate after each disturbance, were also studied. The experimental results first showed that both the creep behavior and stress disturbance promoted the increase of sandstone porosity. A larger loading ratio was associated with more significant impact of stress disturbance on porosity changes. Secondly, the percentage change of macropores during the disturbance creep process was consistent with the change of porosity. Thirdly, the steady-state creep strain and creep strain rate after each disturbance increased with increase of the loading ratio, whereas the steady-state creep strain and creep strain rate after each disturbance decreased with the increase of disturbance frequency. Finally, a positive correlation between creep strain and porosity increment was found. These results can provide theoretical support for surrounding rock stability analysis and mine safety protection under high-intensity mining.