Numerical response and calibration process based on physical tests of clay-rich rocks

This is the authors' abstract. We don't add key points for this paper.

This study presents the calibration and validation of an anisotropic hydro-mechanical constitutive model for Opalinus Clay within the HyMar task of the DECOVALEX (2024-2027) Project. The objective is to reproduce bedding-controlled strength, deformation, strain localization and pore-pressure generation in host rocks, providing a basis for subsequent damage and gas-migration analyses. An anisotropic elasto-viscoplastic model was calibrated against an extensive experimental dataset, including consolidated-undrained triaxial tests on saturated specimens, as well as uniaxial compressive and Brazilian tensile tests on partially saturated samples. Model predictions were compared with measured stress-strain curves, pore-pressure evolution, effective stress paths, peak strengths and post-peak responses across multiple bedding orientations and confinement levels. A baseline parameter set was first defined for a reference orientation, after which anisotropy was introduced by varying the peak friction angle and a softening parameter with bedding inclination. An analysis of spatial heterogeneity and mesh refinement showed that, while the global mechanical response remained unaffected, strain localization patterns were significantly influenced by material variability. Furthermore, the same modeling framework was applied to Callovo-Oxfordian claystone to enable a direct material comparison under identical numerical conditions. The model accurately reproduced the experimentally observed anisotropic behavior, capturing transitions from stiff, quasi-brittle responses to more ductile, hardening-dominated behavior as bedding orientation changed, as well as the associated tensile localization patterns. Compared to Opalinus Clay, Callovo-Oxfordian claystone exhibited a more progressive, hardening-dominated stress-strain response with delayed strain localization. The proposed framework provides a reliable tool for predictive analyses of anisotropic hydro-mechanical processes relevant to repository performance assessment.