Acoustic emission characteristics of rock salt under multi-stage cyclic loading

Abstract

Rock salt is a common sedimentary rock found in the crust and is widely used for underground energy storage and waste disposal. This research conducted multi-stage cyclic loading on impure Huai'an rock salt while monitoring acoustic emissions (AE) in real-time. The results show that as the loading stress increases, the cumulative AE energy increases in a stepwise manner. The frequency distribution displays a band pattern of low, medium, and high frequencies. As the loading stress increases, the proportion of high-frequency signals decreases while that of low-frequency signals increases. The proportion of medium-frequency signals remains consistently the highest. The b-value initially decreases and then increases, with a sharp drop near the failure. Compared to the increased lower limit stress (ILLS), the constant lower limit stress (CLLS) causes higher cumulative AE energy and amplitude, and smaller b-values for the salt samples. These results indicate that the CLLS increases the size of cracks and damage in the salt samples. Based on the RA (risetime/ amplitude)-AF (average frequency) distribution, it is found that the primary mode of failure for rock salt under multi-stage cyclic loading is tensile cracking. Compared to the ILLS, the CLLS promotes the development of shear cracks. The AE test results of the rock salt provide an important basis for explaining the in-situ microseismic signals generated during the operation of salt cavern energy storage.