TIME-DEPENDENT BEHAVIOR OF MAHA SARAKHAM SALT UNDER TRUE TRIAXIAL STRESS STATE

Abstract

True triaxial creep tests are performed to determine the effects of the intermediate principal stress on the time-dependent 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 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 Lode parameter.  The results suggest that the time-dependent deformation calculations based on the conventional creep test results may overestimate the actual closure of cylindrical and spherical caverns by as much as 16% and 35%, respectively.