A model for rock salt, describing transient, stationary, and accelerated creep and dilatancy

In the scope of a unified approach to describe the creep behavior the constitutive model as presented here describes comprehensively the mechanical behavior of rock salt in a good approximation. In this model, hardening is used as an inner variable of state. This model has been verified by the results which were obtained when recalculating a plurality of different laboratory tests. Evidently, hardening is governed by the processes of deformation and recovery on the one hand and by those of damage on the other one, i.e. the formulation of the constitutive laws is based just on those processes of crystal physics which are the origin of the mechanical behavior of salt rock. These considerations have allowed to demonstrate that the hardening-reducing effect of damage can be put on the same level as the dilatancy, the latter being a function both of deformation work performed above the dilatancy boundary (damage work) and minimum stress which has to be determined from triaxial tests. The paper contains a complete set of equations, which are used in model calculations.