True triaxial creep tests are performed to determine the effects of the intermediate principal stress on the timedependent behavior of the Maha Sarakham salt. The applied octahedral shear stresses vary from 5 to 14 MPa while the mean stress is maintained constant at 15 MPa. The loading conditions include conventional triaxial compression, polyaxial and triaxial extension testing. Regression analyses of the results based on the Burgers model indicate that the instantaneous deformation tends to be independent of σ2 . The visco-elastic and visco-plastic parameters notably increase with σ2 . To calculate the σ2 effect on the long-term closure of salt storage caverns the Burgers parameters are defined as a function of the Lode parameter. The results indicate that the conventional creep test results may overestimate the actual closure of cylindrical and spherical caverns by as much as 15% and 35%, respectively.
