Abstract: The rock stress changes periodically during the operation of the salt cavern storage. The dynamic rock cyclic tests on the surrounding rock were carried out， and the influence rules of expansion and damage characteristics of salt rock samples under different axial constant stress and confining pressure cycling cap were analyzed to reveal the influence of stress fluctuations on the stability and tightness of rock. The results showed that volumetric strain curves present a decelerating expansion stage and a steady expansion stage， but there is no significant difference in the cycle’s number of times needed for reaching the stable expansion point of the sample. The smaller the confining pressure cap is or the bigger the constant axial load is， the greater the expansion margin is and the shorter the fatigue life is; the proportion of steady expansion out of uniform expansion is smaller， namely the accelerated expansion points move forward. With the increase of test cycles， the isovolumetric strain ratio becomes smaller and the toughness decreases while the expansion capability increases. The smaller the confining pressure cap is or the bigger the constant axial load is， the faster the loss of toughness capacity is and the stronger the expansion capacity of salt rock is.

Key words: salt rock, fatigue characteristics, volumetric strain, expansion, confining pressure