STUDY OF TERTIARY CREEP OF ROCK-SALT

It appears from macro- and microexperiments that the essential respons e feature beyond the secondary stage of rock salt creep is characteriz ed 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 conse rvation laws ate used to identify the transition from continuous to di scontinuous failure modes. To obtain a continuum tangent stiffness ten sor for bifurcation analyses, a simple creep model is formulated from the modeling framework by combining a viscoplastic part with an implic itly rate-dependent damage part. Sample problems are considered to ill ustrate the proposed procedure.