GeomInt: Geomechanical integrity of host and barrier rocks - experiment, modeling and analysis of discontinuities

Interventions in the geological subsurface, such as the extraction and storage of energy or the safe storage of toxic and radioactive waste, requires careful geoscientific investigations and prognostic studies in the context of different disciplines in order to avoid adverse effects on the environment. In particular, deformation processes and physicochemical alterations can lead to a profound damage to rocks and thus adversely affect the integrity of geological barriers. The various micro- and macro-mechanical structures (fissures, cracks, fractures, etc.) weaken the rock from a mechanical point of view and can lead to unintentional pathways for the migration of pollutants. They can be generalized as discontinuities. Their development is usually inadequately understood and cannot be adequately modeled with currently available simulation systems.

The aim of the collaborative project is to provide a realistic, experimental-numerical analysis of the formation and development of discontinuities in geological barriers using the example of salt, clay and crystalline rocks. The focus is on typical processes that lead to the development of specific discontinuities. These include swelling and shrinkage processes, pressure-driven percolation and stress redistributions.

The GeomInt project is divided into three work packages. Within the first work package, the aim is to investigate pathways caused by swelling and shrinkage processes. For this purpose, various laboratory experiments on clay stones are planned in order to determine material parameters and to observe the formation of discontinuities. One focus of the investigations is on self-healing/self-sealing processes of the clay base. The second work package deals with the development of pathways in salt and clay rocks as a result of pressure-driven percolation. Laboratory experiments will aid in the investigation of the variation in the percolation threshold depending on the stress state and on the temperature of the rock. At the center of the third work package are the pathways that are formed in crystalline rocks due to stress changes. The main focus of the laboratory experiments is crack propagation and the behavior of fractures. The results of the experiments are used in all work packages to simulate the basic processes. While the specific process understanding for the formation and development of the discontinuities considered should be improved with the laboratory experiments, the numerical analyses also serve as progress in methodological understanding. For this purpose, various numerical methods (mesh-based continuum approaches, mesh-free discontinuity methods, hybrid methods) are systematically investigated with regard to their potential and limitations, as well as extended in a suitable manner. In order to check the models developed in this way, field tests carried out in the underground laboratories of Mont Terri (Switzerland), Springen und Reiche Zeche (both Germany) will be analyzed. This also improves the system understanding of the effects of discontinuities on subterranean geosystems. As a result, the project is intended to provide an improved process understanding for the emergence of discontinuities on different time and length scales as well as to provide numerical tools to make the geotechnological use of the subsurface safer and more efficient.

Project period: 01.07.2017 - 30.06.2020

Project partner:

UFZ

CAU

IfG

TUBAF

Uni Stuttgart

BGR