Experimental study of load rate effect of salt rock during loading and unloading

As a typical soft rock, the mechanical properties of salt rock are time-dependent significantly, so the accurate prediction and evaluation of the deformation and damage capacity of salt cavern gas storage during loading and unloading are related to the long-term safe and stable operation of energy reserves. In order to study the rate effect of salt rock, fatigue tests at different loading and unloading rates were conducted. Based on the existing creep constitutive model, the rate effect equation was established to distinguish the creep plastic deformation and loading plastic deformation during loading and unloading. The results show that: (1) The overall fatigue life of salt rock and the proportion of fatigue life in stable deformation stage (the second stage) increase with the increase of loading and unloading rate. (2) The proportion of fatigue life in decelerated deformation stage (the first stage) and the average residual strain of stable deformation stage decrease with the increase of load rate. (3) In the rate-coupled fatigue test, the residual strain decreases with the increase of loading and unloading rate. The creep plastic deformation decreases with the increase of loading and unloading rate. When the loading rate increases from 0.04 kN/s to 5 kN/s, the proportion of creep plastic deformation in the cycle decreases from 85% to 36%, showing a negative exponential relationship. (4) In the full cyclic loading and unloading process, the plastic deformation of loading and creep presents a U-shaped development trend, which corresponds to the three stages of fatigue process of salt rock. The results of this study can lay a foundation for further analysis of creep plasticity and loading plasticity of salt rock.