Acoustic emission characteristics of rock salt under multistage creep-fatigue loading at various temperatures

With the growing global demand for energy, deep underground salt caverns are emerging as a potential solution for large-scale energy storage. In this study, multistage cyclic loading tests were conducted on rock salt at different temperatures in combination with real-time acoustic emission (AE) monitoring. The results show that the cumulative AE count increases stepwise with increasing cyclic stress. The peak frequency is concentrated primarily in the medium-frequency range, exhibiting a band distribution across low-, medium-, and high-frequency ranges. As the temperature increases, the proportion of low-frequency signals decreases from 14.32% to 5.76%, whereas the proportion of medium-frequency signals increases from 85.48% to 94.1%. The proportion of high-frequency signals remains relatively constant between 0.1% and 0.2%. The amplitude-count relationship of the AE signals demonstrates a strong negative power-law correlation. Furthermore, with increasing temperature, the negative power-law exponent of the amplitude gradually decreases, with the b value decreasing from 1.096 to 0.837 and the a value decreasing from 7.4871 to 6.6982. Under all four temperature conditions, the dominant failure mode in rock salt is tensile cracking. However, as the temperature increases, the proportion of tensile cracks decreases from 88.59% to 75.12%, whereas the proportion of shear cracks at 80 °C is nearly double that at 20 °C. This finding indicates that as the temperature increases, the ductility of the material increases, and the crack propagation mode shifts from tensile to shear. This research provides valuable insights for the design and stability assessment of salt cavern reservoirs for deep underground energy storage systems.