Abstract: The surrounding rock of underground gas storage is always under the action of cyclic loading. Constructing a suitable rheological model is the key to analyzing its long-term stability. Based on the principle of stress dissipation, a nonlinear dashpot element(DS-dashpot) and the differential constitutive equation of the DS-dashpot are established. A nonlinear rheological model(PT-DS) is constructed with the connection of Poyhting-Thomson model and the DS-dashpot in series. Meanwhile, a differential constitutive equation of PT-DS model is derived; According to the cyclic loading test process of rock salt specimen, the dynamic stress equation is established, which is divided into the initial uniform loading section and the cyclic load section. According to the analysis of PT-DS model, the constitutive equations of the time-dependent strain at the initial uniform loading and cyclic loading are obtained. The constitutive equation of cyclic loading section is simplified and analyzed and the equations of upper limit line, middle line and lower limit line are obtained. The cyclic loading test process of rock salt specimen are carried out; the test result is fitted using the constitutive equations of the upper limit line, the middle line, and the lower limit line of the PT-DS model; and the corresponding fitting parameters are obtained. The results show that the fitted curve and the simulated curve are very close to the test curve; so the PT-DS model can be used to describe the strain development process under the cyclic loading perfectly.

Key words: cyclic loading, DS-dashpot, PT-DS model, rock salt, nonlinear rheological model