With the project of Jintan underground gas storage

taking the cavity actual bearing conditions as the object of study

carrying out unloading confining pressure test of salt rock under different conditions

the complete stress-strain curves

deformation characteristics are obtained. The test results show that axial and radial strains increase slowly in the initial stage of unloading confining pressure; and the relation between strain and confining pressure is linear. Along with the confining pressure continuous decrease

axial and radial strain values increase sharply. Comparing the loading and unloading curves

under the conditions of the same maximum principal stress

when the unloading confining pressure is the same as triaxial compression pressure value

the axial and radial strains variations are larger than that of loading conditions. Under the same initial stress conditions

the changing magnitude of stress required for rock failure is less than that of triaxial compressive process. It is shown that the plastic deformation of salt rock is different from hard rock of brittle failure under unloading confining pressure. The conclusion can be useful in underground gas storage engineering stability analysis and gas injection/extraction process.