Paper contribution

Analysis of the Mechanical Behavior of Callovo-Oxfordian Claystone under Temperature: Contribution of 3D X-Ray Tomography

Bahaa Abou Chakra; Dragan Grgic; Audrey Bonnelye; Christophe De Lesquen

Proceedings
EUROCK 2026
Pages
497-502
Submitted
28 January 2026
Accepted
15 June 2026
Published
12 August 2026

Summary

Abstract

The Callovo-Oxfordian claystone (COx), as a host rock for radioactive waste storage in France (Cigéo Project), will be subjected to coupled THM (Thermo-Hydro-Mechanical) processes, such as stress variations during excavation, changes in saturation, and thermal fluctuations induced by exothermic waste. To assess the short- and long-term feasibility of geological storage, ensure its safety, and optimize the design, it is essential to analyze the impact of these THM solicitations on the mechanical behavior of the clay host rock. This study investigates the effect of temperature on the mechanical behavior of the COx claystone through triaxial compression tests conducted under confining pressures of 4, 8, and 12 MPa, on samples oriented both parallel and perpendicular to the bedding plane. The tests, performed between 20 and 90 °C with a heating rate of 10 °C/h, revealed a slight decrease in peak strength with temperature increase for the perpendicular orientation. This phenomenon results from interstitial fluid overpressure induced by the difference in thermal expansion between the water and the solid skeleton of the claystone, which induces thermo-mechanical damage. X-ray 3D tomography was used to analyze the evolution of fractures between the initial state (after core sampling) and the final state (after the mechanical test). This approach provides a detailed assessment of the temperature’s impact on the morphology of the fracture network, thereby improving the understanding of the deformation mechanisms and the influence of thermo-hydro-mechanical stresses on the COx behavior. At room temperature, pre-existing fractures tend to open in samples oriented parallel to the bedding, while they tend to close in those perpendicular to it. The influence of temperature on these mechanisms is currently being further investigated as part of ongoing research.

Contributors

Authors

  1. Bahaa Abou Chakra Université Lorraine, France; National Agency for Radioactive Waste Management (Andra)
  2. Dragan Grgic Université Lorraine, France
  3. Audrey Bonnelye Université Lorraine, France
  4. Christophe De Lesquen National Agency for Radioactive Waste Management (Andra)

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References

  1. Belmokhtar M. (2017) Contributions à l’étude du comportement thermo-hydro-mécanique de l’argilite du Callovo-Oxfordien (France) et de l’argile à Opalinus (Suisse). Thèse de doctorat, Université Paris-Est.https://pastel.hal.science/tel-01630492
  2. Conil N., Talandier J., Djizanne H. N., de La Vaissière R., Righini-Waz C., Auvray C., Morlot C., Armand G. (2018) How Rock Samples Can Be Representative of in Situ Condition: A Case Study of Callovo-Oxfordian Claystones. Journal of Rock Mechanics and Geotechnical Engineering. pp. 613‑623. https://doi.org/10.1016/j.jrmge.2018.02.004
  3. Gbewade C., Grgic D. Giraud A., Schoumacker L. (2023) Experimental Study of the Effect of Temperature on the Mechanical Properties of the Callovo-Oxfordian Claystone. Rock Mechanics and Rock Engineering, pp. 1‑22. https://doi.org/10.1007/s00603-023-03630-7
  4. Grgic D., Moumni M., Giraud A., De La Vaissière R., Talandier J. (2023) Water Permeability Measurements by Steady-State and Pulse Decay Methods on the Callovo-Oxfordian Claystone and Impact on Its Mechanical Properties. Rock Mechanics and Rock Engineering. https://doi.org/10.1007/s00603-023-03340-0
  5. Liu Z., Shao J., Xie S. Y., Conil N., Talandier, J. (2019) Mechanical Behavior of Claystone in Lateral Decompression Test and Thermal Effect. Rock Mechanics and Rock Engineering. https://doi.org/10.1007/s00603-018-1573-3
  6. Mohajerani M. (2011). Etude expérimentale du comportement thermo-hydro-mécanique de l’argilite du Callovo-Oxfordien. Thèse de doctorat, Université Paris-Est. https://pastel.hal.science/pastel-00647890
  7. Shi H. L., Hosdez J., Rougelot T., Xie S. Y., Shao J. F., Talandier J. (2021) Analysis of Local Creep Strain Field and Cracking Process in Claystone by X-Ray Micro-Tomography and Digital Volume Correlation. Rock Mechanics and Rock Engineering. pp. 1937‑52. https://doi.org/10.1007/s00603-021-02375-5
  8. SouleyM., De Lesquen C., Vu M. N., Armand G. (2026) Advanced Thermo-Hydro-Mechanical Modelling of Callovo-Oxfordian Claystone: Temperature Effects and Multi-Scale Applications for Geological Disposal Safety. International Journal of Rock Mechanics and Mining Sciences. Volume 199. https://doi.org/10.1016/j.ijrmms.2026.106397
  9. Wang C., Xie S., Shao J. F., Vu M. N., De Lesquen C. (2026) On the Thermal Effects of Mechanical Behavior in the Callovo-Oxfordian Claystone. International Journal of Rock Mechanics and Mining Sciences. https://doi.org/10.1016/j.ijrmms.2025.106367
  10. Zhang C. L. (2017) Examination of Effective Stress in Clay Rock. Journal of Rock Mechanics and Geotechnical Engineering. pp. 479‑89. https://doi.org/10.1016/j.jrmge.2016.07.008
  11. Zhang C. L., Conil N., Armand, G. (2017). Thermal Effects on Clay Rocks for Deep Disposal of High-Level Radioactive Waste. Journal of Rock Mechanics and Geotechnical Engineering. pp. 463‑78. https://doi.org/10.1016/j.jrmge.2016.08.006
  12. Zhang F., Hu D. W., Xie S. Y., Shao J. F. (2014) Influences of Temperature and Water Content on Mechanical Property of Argillite. European Journal of Environmental and Civil Engineering. pp. 173‑89. https://doi.org/10.1080/19648189.2013.852485
  13. Zhang F., Xie S. Y., Hu D. W., Shao J. F., Gatmiri. B. (2012) Effect of Water Content and Structural Anisotropy on Mechanical Property of Claystone. Applied Clay Science. pp. 79‑86. https://doi.org/10.1016/j.clay.2012.09.024
  14. Zhang W. (2021) Contribution à l’étude expérimentale du comportement mécanique des argilites du Callovo-Oxfordien : effets du chemin de chargement et de la température. Thèse de doctorat, Université de Lille. https://theses.fr/2021LILUN037