Abstract: 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.

Key words: salt rock, confining pressure unloading, expansion characteristics, axial pressure effect, dilatation