The influence of holding stress levels on the creep-fatigue interaction of rock salt based on DEM simulation

Abstract

<p>The compressed air energy storage (CAES) system within an underground salt cavern encompasses charging, idle, and discharging stages. These stages involve the periodic injection and withdrawal of air pressure, exerting a combination of creep and fatigue on the surrounding rock at varying stress levels. This study employed PFC^2D to conduct creep-fatigue simulation tests on rock salt, utilizing the Burger's and linear parallel bond (LPB) models to concurrently simulate time-dependent and damage behavior. Results indicated that as the holding stress interval increased, both the creep-fatigue life and fracture time decreased. Time-dependent damage and cyclic loading damage exhibited detrimental interactions at all holding stress levels, except for the minimum cyclic stress. Higher holding stress levels led to an increased creep fraction and a reduced fatigue fraction, causing the salt simulation model to display a tendency towards static creep behavior. Cumulative crack numbers demonstrated a stepwise increase in relation to loading time, with higher holding stress levels generally inducing a greater number of cracks. Following fracture, the salt simulation models exhibited a prominent, inclined macrocrack, as well as numerous micro-cracks primarily surrounding the macrocrack. These findings underscore the importance of understanding the impact of different loading stages on rock salt behavior in CAES systems, offering valuable insights for design and operation optimization.</p>