Acoustic emission characteristics and energy evolution of salt rock for deep-salt-cavern engineering under triaxial loading and unloading

Deep salt cavern gas storage is subjected to periodic high stress load during operation. To explore the damage and deformation characteristics of salt rock under triaxial cyclic loading and unloading, the MTS815 rock mechanics test system and acoustic emission (AE) signal acquisition system were used, and the effects of confining pressure and loading and unloading on the characteristics of AE and energy evolution of the whole cycle were analyzed. The results showed that: 1) as the confining pressure increased from 10 MPa to 30 MPa, the cumulative AE counts in the compaction stage decreased by 86%. Kaiser effect was obvious before the peak stress point, and the Felicity ratio was negatively correlated with the number of cycles; 2) With the increase of deviatoric stress, the growth rate of elastic energy( U c ) and dissipated energy( U d ) increased gradually. Under the same deviatoric stress, the deformation and dissipation energy of high confining pressure specimen were smaller, when it reached the same stress; 3) Both U c and U d showed two-stage growth trend during the test. At the same strain level, with the increase of confining pressure U c and U d increased as MnMolecular function, when the confining pressure effect strengthened. Considering the confining pressure, the coupling equation of AE ringing count and U d during loading and unloading was established and verified. It has certain guiding significance for the safe operation of deep salt cavern gas storage.