Results of true triaxial strength tests on rock salt

Abstract Knowledge of the thermomechanical properties of rock salt is important for the dimensioning of a permanent repository for radioactive wastes in a salt dome and for the necessary safety analysis, as well as for the design of mines and caverns. Therefore, research is conducted by the BGR on the creep and failure behavior of rock salt. Equations have been derived which describe strength and creep under various conditions. They are needed mainly for finite element model calculations. A true triaxial test rig for cubic samples has been used to conduct several test series on different types of rock salt. The effects of varying hydrostatic (mean) stress, load path (load geometry), and temperature on strength and residual strength are discussed. Strength is defined as the maximum octahedral shear stress in a test. A failure law in the sense of a conservative strength limit has been developed for a typical rock salt on the basis of an extended Drucker-Prager law and the experimental results. The law describes the influence of mean stress, load path, and temperature on strength and residual strength.