Speaker
Description
The safety assessment of radioactive waste repositories depends on a fundamental understanding of coupled hydro-mechanical (HM) processes in the near-field. In this study, we investigate the desiccation-induced fracturing of Opalinus Clay, a potential host rock, triggered by seasonal ventilation in underground galleries. We specifically focus on the Cyclic-Deformation (CD-A) experiment at the Mont Terri Rock Laboratory (Switzerland), where seasonal variations in relative humidity (RH) lead to significant near-surface crack networks as described in Ziefle et al. (2024) and Cajuhi et al. (2024). To capture the transition from a continuous to a discontinuous porous medium, we employ a variational phase-field method for fracture coupled with an HM process model. This framework allows for the simulation of complex crack initiation and propagation without pre-defined fracture paths. The numerical setup incorporates in-situ RH monitoring data as boundary conditions, ensuring a link between environmental forcing and the mechanical response of the porous matrix.
Validation is performed by comparing numerical results with field observations documented by Ziefle et al. (2024), including moisture content evolution and electrical resistivity measurements. The model successfully reproduces the spatial distribution of observed cracks and identifies the specific RH ranges at which failure occurs. Beyond simple reproduction of field data, the simulations confirm a dual control mechanism where desiccation serves as the primary driver of failure, while the precise timing and location of crack initiation are governed by stress concentrations arising from geometric irregularities in the excavation. These features lead to earlier fracturing compared to idealized geometries, highlighting the importance of the actual morphology in predictive models. Furthermore, this work provides insights into the temporal dynamics of fracture evolution, helping to fill knowledge gaps left by field data, which might typically capture final fracture states. Ultimately, by benchmarking against the CD-A dataset, this study demonstrates that combining detailed underground research laboratory (URL) monitoring with advanced phase-field modeling significantly improves the ability to predict damage zones in the near-field environment.
Cajuhi, T., Ziefle, G., Maßmann, J., Nagel, T., & Yoshioka, K. (2024). Modeling desiccation cracks in Opalinus Clay at field scale with the phase-field approach. InterPore Journal, 1(1), ipj260424-7.
Ziefle, G., Cajuhi, T., Costabel, S., Furche, M., & Maßmann, J. (2024). Water Content Evolution in the EDZ of Opalinus Clay: A Methodic Approach for a Comparative Interpretation of Measurements and Modelling. Rock Mechanics & Rock Engineering, 57(6).
| Country | Germany |
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