Nonlinear creep-damage constitutive model of surrounding rock in salt cavern reservoir

Salt cavern energy storage is a key technology to promote the optimization of China's energy reserve structure, but the surrounding rock of the reservoir cavity is prone to creep and damage during the long-term injection production process, which seriously endangers the safety of the reservoir operation. Therefore, it is urgent to carry out salt rock creep test research to reveal the creep mechanical properties and damage evolution failure mechanism of the surrounding rock of the reservoir cavity, so as to provide a theoretical basis for the safe construction and operation of the salt cavern reservoir. In order to deeply study the creep mechanical properties of salt rock, a long-term graded loading creep test was carried out on salt rock specimens. The loading time of each stage was about 30 days, and the total creep time exceeded 3 months. The long-term strength of salt rock is determined to be about 8 MPa by the improved isochronous stress-strain method and steady-state creep rate method. A nonlinear creep-damage constitutive model of salt rock based on elastic element and dashpot element is established and compared with the fitting results of several models for the sake of describing the creep behavior of salt rock more accurately. The local and global sensitivity analysis methods are applied to the model to verify its robustness and the rationality of parameter setting. The results showed that the fitting results of the model were in good agreement with the test data, and could well describe the whole creep process of salt rock, especially the nonlinear accelerated creep stage. In addition, the constitutive relation of the established model is simple, and the meaning of the model parameters is clear, which provides a theoretical basis for the study of the creep law of salt rock and the safe operation of the salt cavern storage.