Analysis of axial creep properties of salt rock under low frequency cyclic loading using Burgers model

In order to study the creep properties of salt rock under low frequency cyclic loading, creep tests on salt rock samples under low frequency cyclic loading are carried out by adopting the loading mode of cyclic confining pressure with a constant axial stress. The test results show that up to a certain time, the axial creep curves of salt rock are smooth; while after that point, the axial creep curves clearly fluctuate with the confining pressure. Overall, the axial creep curves of salt rock under low frequency cyclic loading are similar to that of Burgers model. According to the connection relation of component creep model, the Burgers model is divided into Maxwell model and Kelvin model. The axial creep equations of Maxwell model and Kelvin model under the loading mode of cyclic confining pressure with a constant axial stress are deduced respectively in the superposition condition that the fatigue failure of material is neglected, and the effect of loading cycle on the models are also analyzed. Then, by combining the axial creep equations of Maxwell model and Kelvin model, the axial creep equation of Burgers model under cyclic loading is obtained; and the reasonability of which is verified by using the creep test data of salt rock. The result indicates that fitting curves and test curves conform well each other; and the proposed model can well reflect the creep properties of salt rock under cyclic loading, especially the fluctuation of creep deformation with loading change.