CREEP DEFORMATIONS OF SALT MINE PILLARS UNDER COMPRESSED-AIR ENERGY STORAGE OPERATION

Abstract

ABSTRACT

Series of triaxial cyclic loading tests have been performed to predict the time-dependent deformation of supported pillars in abandoned salt mines planned for a compressed-air energy storage operation. The salt specimens are prepared to obtain rectangular prisms with nominal dimensions of 54´54´108 mm.  The applied axial and lateral cyclic stresses depend on mining depths, extraction ratios and injection pressures. The confining pressures vary from 20% (withdrawal) to 90% (injection) of the in-situ stresses.  The stress conditions are calculated for the depths from 250 to 400 m with extraction ratios ranging from 30 to 60%.  All tests are performed up to 21 days.  Each cycle takes 24 hours.  The steady-state creep strains are calculated in terms of the octahedral shear strains as a function of time.  The cyclic loading induces a higher creep strain than that of the static loading for all depths and extraction ratios, suggesting that the time-dependent deformations of salt pillars are greater under cyclic loading than under static loading.  The distortional strain energy at failure is used to predict the time-dependent strengths of the salt pillars. The results suggest that under storage operation the duration under stable condition of the salt pillars decreases with increasing extraction ratios and mining depths. 

KEYWORDS: Time-dependency, Creep, Strain Energy Density, Potential Creep Law, Extraction Ratio