A Modified Creep Model for Cyclic Characterization of Rock Salt Considering the Effects of the Mean Stress, Half-Amplitude and Cycle Period

The fluctuation of the operation pressure during injection and withdrawal is a key factor affecting the long-term stability of surrounding rock in a compressed air energy storage (CAES) cavern. To assess the mechanical behavior of rock salt under different pressure fluctuations and to optimize the operating parameters of CAES caverns, uniaxial cyclic loading tests under the sine condition were carried out by changing three cycle parameters, namely the mean stress, half-amplitude and cycle period. The test results show that the deformation behavior during cyclic loading tests can be divided into transient, steady, and accelerated stages, which is similar to that of creep tests. The strain and steady strain rates increase with increasing cycle parameters, showing a nonlinear deformation property of rock salt under cyclic loading. To describe the nonlinear response that cannot be captured by the Burgers model, a stiffness scaling factor is proposed based on the test results. A modified cyclic creep model of rock salt is established by introducing this stiffness scaling factor into the conventional Burgers creep model. The agreement with the experimental data indicates that the modified cyclic creep model can accurately reflect the influence of the three cyclic parameters on the deformation properties of rock salt.