A rate-dependent model for the ductile behavior of salt rocks

Salt rocks, such as potash and rock salt, show a complex mechanical behavio r that is rate and history dependent. Various approaches exist to represent the main features of the response of these rocks through constitutive mode ls. The approach proposed in this paper is to formulate the constitutive eq uations using internal state variables (ISV) in the context of the unified theory of inelastic flow. To illustrate the application of this approach, t he authors use an updated version of a viscoplastic model with reduced expr essions for laboratory triaxial tests at relatively high confining pressure . It is shown that, under these conditions, mixed hardening of salt rocks c an be described through a combination of scalar and directional ISV. The au thors also describe in some detail a procedure to obtain the material param eters for the model equations. The paper shows some characteristics of the model response for various loading paths, illustrating the good agreement w ith experimental observations and highlighting some of the differences with a classical isotropic hardening model.