Study of tertiary creep of rock salt

It appears from macro- and microexperiments that the essential response feature beyond the secondary stage of rock salt creep is characterized by the evolution of localized damage that results in the formation and propagation of macrocracks. To predict the creep response of rock salt, a modeling framework with a corresponding integration scheme is developed based on thermodynamic restrictions. The jump forms of conservation laws ate used to identify the transition from continuous to discontinuous failure modes. To obtain a continuum tangent stiffness tensor for bifurcation analyses, a simple creep model is formulated from the modeling framework by combining a viscoplastic part with an implicitly rate-dependent damage part. Sample problems are considered to illustrate the proposed procedure.