Nonlinear creep model of salt rock used for displacement prediction of salt cavern gas storage

To explore the creep response and unloading rebound effect of salt rock, uniaxial compression creep and unloading rebound tests are performed at different axial stresses on salt rock specimens. The test results indicate that the instantaneous strain generated by salt rock mainly contributes by unrecoverable instantaneous plastic strain under a higher axial stress, and the creep strain mainly consists of unrecoverable visco-plastic creep strain. The ratio of visco-plastic creep strain to the total creep strain gradually increases with increases in time and axial stress. A hardening viscous body and a damage viscous body are proposed to describe the hardening effect and damage effect of rock during the creep process. Subsequently, a new five-component nonlinear creep model is established by connecting the two viscous bodies with the conventional elastic body and Kelvin model in series. The creep and unloading rebound test data of salt rock are utilized to testify the reasonability of the nonlinear creep model. The results indicate that the theoretical curves of the nonlinear creep model exhibit good coherence to the test data in the creep and unloading stages. Based on the secondary development platform of the FLAC3D software, the nonlinear creep model is redeveloped to obtain the computer application program. Thus, the creep and unloading rebound test of salt rock is simulated using the secondary development program of the nonlinear creep model. In general, the results from the numerical simulation and creep and unloading rebound test of salt rock are in good agreement, and this proves the accuracy of the secondary development program of the nonlinear creep model. Finally, the computer application program of the model is utilized to predict the surrounding rock deformation of a salt cavern gas storage during operation.