Through the confining pressure unloading experiments

the dilatation characteristics of salt rock under different triaxial stress states unloading pressure

and the relationship between dilatation and unloading method are researched. The results show that: (1) There is a logarithmic relationship between volumetric expansion of capacity and deviatoric stress during unloading confining tests. (2) Initial confining pressure value hardly effects the dilation of salt rock. The growth of axial pressure can promote the dilation

and make the accelerated-expansion-point appear forward. Meanwhile

the corresponding deviatoric stress linearly increases with the axial pressure. (3) With the increase of deviatoric stress

the expansion coefficient of salt rock (ratio of lateral strain to longitudinal deformation) will increase linearly at the beginning; and then exponentially.