Nuclear waste disposal in Germany is planned in deep rock formations that act as a barrier over geological time periods. The long-term protective effect of the geological barrier(s) depends on many factors, especially geological processes, many of which are related to the tectonic stress field. Knowledge of the stress state is therefore not only relevant for the construction of the underground repository, but also for assessing its long-term stability. However, a reliable stress prediction in the run-up to exploration measures is made difficult by the fact that only few measurement data are available and the stress field is not uniform in its orientation and magnitude. In fact, depending on the subsurface structure (lithologies, faults), significant local deviations from the nationally known stress distribution can occur.
In order to achieve a better understanding of this spatial variability of the stress field, the project SpannEnD (2018-2022) created the first geomechanical-numerical 3D stress models for Germany. These models were calibrated on point-measured stress data and allow predictions for areas without stress data and the derivation of all six independent components of the stress tensor based on continuum mechanical approaches. Since no database for stress magnitudes existed so far, one was created for Germany and neighbouring regions as part of the project. The stress tensor of the German model was used to determine the slip tendency for several compilations of fault geometries. This parameter is used to estimate the reactivation potential of faults. In addition, first approaches of stress transfer between models of different sizes were tested, as well as methods of scaling rock paroperties.
The SpannEnD II project (2022-2026) is particularly concerned with the further development and refinement of the stress model for Germany. With regard to improved model calibration, the stress database will also be expanded. At the same time, sub-modelling techniques will be further developed and integrated into a workflow that allows the linking of the Germany model with sub-area and site models. This methodology is to be tested on two sub-areas. Furthermore, an improved quantitative assessment of the procedures for in-situ stress measurements will be carried out. Based on this, an intelligent sampling strategy for future drilling programmes will be developed, which will lead to the greatest possible reduction of uncertainties in the stress forecast.