The starting point for conducting reliable geomechanical assessments is the establishment of a physically plausible, well-founded, and realistic characterisation of material behavior. The IfG is commited in the continuous development and enhancement of material models for salt rocks, overburden, and stratum surfaces, thereby setting the state of the art in salt mechanics. The material models are integrated in the numerical codes FLAC, FLAC3D, UDEC, and 3DEC, developed by ITASCA.
The Günther-Salzer constitutive model (IfG-GS) is an elasto-visco-plastic model for ductile salt rocks that assigns essential microstructural processes to macroscopic parameters and adapts their interaction. Using dilatancy as the sole internal state variable for the damage state, the model describes all three creep phases characteristic of salt rocks (TCC conditions) as well as the strength behavior under TC conditions in a consistent manner, depending on velocity and temperature, using a uniform set of parameters. All model parameters can be derived from conventional TCC and TC tests with dilatancy measurement. Due to the close physically based link between the viscosity of the creep model and the dilatancy, it is possible, among other things, to describe the strength for all loading speeds as consistently and effortlessly as the consolidation and fatigue behavior under cyclic loading, without having to parameterize these effects separately, e.g., by means of a special strength characteristic curve.
This model is therefore particularly suitable for modeling and predicting service life-related softening in long-term convergence processes or the complex softening and hardening behavior under cyclic loads, such as in storage mining.
The extended strain hardening approach has been tested extensively in research projects and mining practice. Details can be found in Günther (2009), Günther & Salzer (2012), Hampel et al. (2016), Hampel et al. (2022).
The visco-elasto-plastic material model according to Minkley (IfG-MI) describes the stress and deformation behavior of salt rocks within the framework of a modular rheological model concept. It is based on a superposition of rheological model bodies, each of which represents characteristic properties or deformation mechanisms of salt rocks. Damage-free primary and secondary creep is represented, for example, by a nonlinear Burgers model, whereas the distinctly nonlinear strength and softening behavior of salt rocks is described by a modified nonlinear Mohr-Coulomb model (within the framework of a St.-Venant element). This model concept is particularly suitable for reproducing extremely rapid softening processes during the failure of brittle salt rocks (e.g., carnallite). Only in this way is it possible to investigate and predict the dynamic excitation of load-bearing elements (e.g., in potash mining) caused by failure-induced load redistribution and the resulting risk of rock bursts, as well as to calculate the associated release of seismic energy in the model (e.g., Völkershausen 1989, Teutschenthal 1994).
It has been validated in research projects and has been used for numerous mining projects for 20 years. Details can be found in Minkley, W. (2004); Hampel, A. et al. (2016) and Hampel, A. et al. (2022).
The layered surfaces in salt rock are characterized by a nonlinear dependence of shear strength on normal stress and adhesive strength behavior with velocity- and displacement-dependent softening. For example, rock bursts in construction areas with very compact pillars can only be explained if the sudden softening after exceeding a dynamic shear strength is considered.
The adhesive shear model according to Minkley can represent this behavior for static and dynamic load cases. For further information, see, for example, Minkley & Mühlbauer (2007), Minkley, Mühlbauer, Lüdeling (2016) or Knauth (2018).
The extended strain hardening approach (IfG-GS) can optionally be supplemented with additional variants: