Discontinuous fatigue of salt rock with low-stress intervals

When used as compressive air energy storages, underground salt caverns are often subjected to discontinuous cyclic force, characterized by low-stress time intervals (LSIs). In this study, discontinuous cyclic loading tests were conducted to evaluate the effect of LSIs on the fatigue performance of salt rock. The results show that the fatigue life of the specimen subjected to discontinuous cyclic compression decreased sharply in comparison with conventional fatigue tests (i.e. continuous cyclic loading tests). The residual strain in S cycles (which follow the LSIs) developed more rapidly than in N cycles (where there is no preceding LSI). Elastic axial deformation in S cycles was smaller, whereas the elastic lateral deformation is zero both in S cycles and N cycles. Similar phenomena for discontinuous fatigue were also observed in discontinuous cyclic shear tests. The mechanism of discontinuous fatigue is the dislocation-related Bauschinger effect which is induced by reverse movement under residual stress during LSIs.