Post-yield plastic frictional parameters of a rock salt using the concept of mobilized strength

Salt slabbing, spalling and fallout surrounding underground salt storage cavern are closely associated with the nonlinear deformability and post-yield property of rock salt. A better understanding of the pre- and post-yield behavior of rock salt helps the designer in predicting displacements and failure zones around the salt cavity more accurately, as well as in the optimizing design and operation. In the present study, an approach to determine Youngʹs modulus and Poissonʹs ratio from triaxial test plots has been discussed. A series of compression tests was performed to explore the nonlinear deformability and post-yield strength properties of a rock salt. The rock salt specimens were prepared from Jintan salt deposit, China. It is found that the error in modulus obtained by directly computing the gradient of stress strain curve is relatively small and can be used in analysis. However, error in Poissonʹs ratio is large. The post-yield strength characteristics were described by nonlinear empirical evolution law of mobilized strength components with maximum principal strain during the process of strain softening/hardening. The proposed generalized Mohr–Coulomb strength criterion with cohesion-weakening and frictional- strengthening was proved effective to capture the post-yield behavior of rock salt.