Micro-macroscale creep behaviors of salt rock subjected to thermal shock and associated constitutive model
Cheng Lyu, Wuqiang Cai, Tao Deng, Shengzhi Wu, Xiao Zhang
Abstract
To elucidate the cyclic creep mechanisms in China's impure salt rock after high-temperature damage, cyclic nanoindentation and uniaxial cyclic loading tests were conducted at 25 °C, 100 °C, 120 °C, and 160 °C in this study. The results revealed that under cyclic nanoindentation, gypsum mineral exhibited significantly lower indentation depths compared to halite and ankerite minerals, indicating superior resistance to deformation. Additionally, the results demonstrated that high temperature significantly enhances the creep behavior. The maximum indentation depth and creep displacement of minerals, as well as the maximum deformation and creep strain of rock cores, all followed an exponential increase with rising temperatures, with the rate of increase accelerating at higher temperatures. Importantly, it was found that mineral deformation is not the dominant factor in the overall deformation of rock cores; however, the behavior of the mineral phases fundamentally governs the salt rock's mechanical response under stress. Based on these findings, a new constitutive model for cyclic creep was established based on fractional derivatives to accurately characterize the nonlinear cyclic creep characteristics of impure salt rocks at different scales. This model was validated against test data, effectively representing the periodic fluctuations in indentation depth or strain, particularly during the accelerated creep stage. Furthermore, a temperature-dependent correction parameter was introduced, along with a modified Mori-Tanaka method, to upscale microscale results to the macroscale across varying temperatures. This study provides a theoretical foundation for predicting deformation and assessing the stability of salt cavern walls under high-temperature and cyclic loading conditions in deep geological settings.