ABSTRACT
In the paper two equivalent constitutive equations for rock salt (of creep and relaxation type) with loading dependent instantaneous response are derived, for experiments carried out either with stress control or with the deformation control. Our new constitutive equations describe the behavior of rock type materials relative to a configuration which was previously deformed under possible unknown large deformations, a typical feature for rocks. The rock salt compressibility and dilatancy are also described by the model. To high loading rate the rock behavior is quite different from creep (or relaxation) tests and the irreversible deformations appear in our model even for small stresses. From the propagation equation we emphasize the existence of the elastic waves as well as the non-elastic waves. The stability of the elasto-plastic process and the uniqueness of the solution of the variational inequality related to the quasi-static boundary problem are also proved.
