Material Approach for Opalinus Clay

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Mohammadreza Jalali

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+49 241 80 96794

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Material Approach for Opalinus Clay

Funding: Swiss Federal Nuclear Safety Inspectorate (ENSI)

Project term: 2018 - 2021

 

Opalinus clay, a Mesozoic shale formation of about 180 million years in age, has been selected as the potential host rock for disposal of high- and low-level nuclear waste in Switzerland. Some of the beneficial characteristics of this formation are the low hydraulic conductivity, the high radionuclide retention potential, and the potential of self-sealing of open cracks and fissures. The heterogeneity of the characteristic parameters such as hydraulic conductivity, diffusion coefficients and mechanical properties and the influence of layering play key roles in the characterization of these clay-rich formations.

Hydro-mechanical characterization of Opalinus Clay under undrained short-term and drained long-term conditions can improve understanding of

  • The governing mechanical behavior of Opalinus Clay
  • The dependency of its geomechanical and petrophysical properties on the effective stress state
  • Its strength at a saturated state
  • The short-term pore pressure evolution during triaxial testing and tunnel excavation
  • The processes that control the formation of excavation damage zones, called EDZ, around tunnels and galleries
  • The influence of excess pore pressure dissipation on the EDZ and tunnel deformations.

The ongoing project comprises a series of HM-coupled laboratory experiments and numerical simulations to characterize the geomechanical and hydromechanical properties and behavior of intact Opalinus Clay. The ongoing laboratory experiments complement previous laboratory experiments such as unconsolidated undrained tests (Amann et al. 2011, 2012), unconfined compression and indirect tensile strength tests on specimens equilibrated at various relative humidity (Wild et al. 2015a), and consolidated undrained and drained triaxial tests on fully re-saturated specimens (Wild et al. 2015b). For numerical simulations a transverse-isotropic elastoplastic model will be developed that will be benchmarked against above mentioned laboratory tests.

References

Amann, F., Button, E. A., Evans, K. F., Gischig, V. S., & Blu¨mel, M. (2011). Experimental study of the brittle behavior of clay shale in short-term unconfined compression. Rock Mechanics and Rock Engineering, 44(4), 415–430.

Amann, F., Kaiser, P. K., & Button, E. A. (2012). Experimental study of the brittle behavior of clay shale in rapid triaxial compression. Rock Mechanics and Rock Engineering, 45(1), 21–33.

Wild, K. M., Wymann, L. P, Zimmer, S., Thoeny, R., & Amann, F. (2015a). Water retention characteristics and state-dependent mechanical and petro-physical properties of a clay shale. Rock Mechanics and Rock Engineering, 48, 427–439.

Wild, K. M., Amann, F., & Martin, C. D. (2015b). Dilatancy of clay shales and its impact on pore pressure evolution and effective stress for different triaxial stress paths. In Proceedings of the 49th US Rock Mechanics/Geomechanics Symposium, American Rock Mechanics Association.