A general constitutive equation for transient and stationary creep of rock salt

A constitutive equation, which besides creep describes volumetric dilatancy and/or compressibility, is subjected to some restrictions if we would like it to describe both stationary and transient creep. These general formulations are discussed here. A procedure to determine a viscoplastic potential for stationary creep from experimental data is presented. An example is given for rock salt, but the procedure is quite general and can be used for any creeping geomaterial, possessing the property of being either dilatant or compressible. Comparison of the model prediction with the data is presented. Long-term failure, or creep-failure, is also considered. Typical mining examples of creep, wall convergence for both short-term failure and long-term failure are given for vertical shafts or boreholes. Other examples will be given elsewhere.