Experimental research on mechanical characteristics of salt rock under triaxial unloading test

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.