EGU General Assembly 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

Exploring and modeling the formation of desiccation cracks in Opalinus Clay at field scale

Tuanny Cajuhi1, Gesa Ziefle1, Jobst Maßmann1, and Keita Yoshioka2,3
Tuanny Cajuhi et al.
  • 1Federal Institute for Geosciences and Natural Resources (BGR), Germany
  • 2Department of Petroleum Engineering, Montanuniversität Leoben, Austria
  • 3Department of Environmental Informatics, Helmholtz Centre for Environmental Research (UFZ), Germany

Opalinus Clay (OPA) has been one of the main focuses of international geoscientific research due to its potential use as a host rock for the storage of heat-generating radioactive waste. In-situ experiments taking place in the Mont Terri Rock Laboratory in Switzerland provide valuable insights into the material properties and behavior of OPA. The Cyclic Deformation (CD-A) experiment has been conducted since October 2019 in the rock laboratory to investigate hydro-mechanical effects through long-term direct and indirect measurements such as resistivity, water content, suction, and crack development. Desaturation effects due to variations in relative air humidity induced by ventilation and seasonal changes, drive the formation of desiccation cracks at the walls of the CD-A niches.

We use a mathematical model based on a macroscopic poromechanical and on the phase-field approaches to compute desiccation. The formulation consists of the balance equations of the solid and liquid phases and of the crack phase-field evolution equation. Within this combined framework, we are able to account for the drying of the niche and for desiccation cracks. Our solution scheme is implemented in the open-source finite element software OpenGeoSys (OGS 6).

In this contribution, we discuss the practical steps for applying the poromechanical phase-field approach at in-situ scale. The basic steps consist of determining the material properties and computing the fracture energy and characteristic length. Moreover, we use field data concerning the crack aperture to deduce the crack resolution for the simulations. The model setup consists of a quarter cross-section of a CD-A niche. We compare the modeled crack response with the monitored cracks at field scale and evaluate whether they initiate and propagate according to the monitored relative air humidity range. Furthermore, we assess the impact of randomly distributed material properties, e.g. fracture energy, and changes in permeability due to cracking.

How to cite: Cajuhi, T., Ziefle, G., Maßmann, J., and Yoshioka, K.: Exploring and modeling the formation of desiccation cracks in Opalinus Clay at field scale, EGU General Assembly 2023, Vienna, Austria, 24–28 Apr 2023, EGU23-11202,, 2023.