Study on visco-elastoplastic fractional creep model of surrounding rock of salt cavern gas storage

The cavities formed by the water solution mining of underground salt mines is an ideal storage place for natural gas, which has the advantages of superior sealing properties, low construction expenses, ample storage capacity, and high peak regulating efficiency. However, during the years of operation in the salt cavity gas storage, the salt rock will inevitably creep, which will jeopardize the entire underground cavity. Therefore, it is essential to conduct further research on the creep properties of salt rock to maintain the security and stability of salt cavern storage. In this paper, a 210-day triaxial compression test was conducted to analyze the creep characteristics of salt rock, and an improved isochronal stress-strain inflection point approach was put forward. This enhanced method reduces the subjective influence of the traditional method on the selection of the inflection point, and the result is more accurate, which provides valuable information for estimating the effective life of the salt cavity gas storage. This paper used a nonlinear visco-elastoplastic body to characterize the accelerated creep strain char-acteristics of rock and combined it with the Hooke body and fractional-order element to derive a novel creep constitutive model. The new model is in good accordance with the experimental results, which could accurately capture the entire process of salt rock creep and serve as a theoretical foundation for the research of creep characteristics and the stable running of salt rock gas storage.