Insights into the Anisotropic, Hydro-Mechanical Behavior of Opalinus Clay Through Experimental and Microstructural Investigations
Notice bibliographique
Résumé
ABSTRACT: For analyzing the influence of structural anisotropy on the hydro-mechanical behavior of a clay shale, we performed three consolidated, undrained triaxial compression tests with different geometric specimen configurations. Opalinus Clay specimens were tested with bedding plane orientations of 30°, 60°, and 90° with respect to the horizontal. Results indicated different peak strengths at failure with highest and lowest values for the 90° and 30°-specimens, respectively. Failure occurred at different mean effective stresses with different magnitudes of pore water pressure built up. The 30°-specimen showed a decreasing effective mean stress up to and beyond failure compared to the initial effective consolidation stress of 10 MPa, while the 90°-specimen increased in effective mean stress during undrained loading. Dilation was found to be highest in the 30°-specimen and lowest in the 60°-specimen, demonstrated by both the effective stress path and the post-experimental microstructural analysis of the shear zones. The macroscopic shear band formed parallel to the bedding plane orientation for the specimen loaded in 60°-orientation. Here, only minor microstructural fabric changes such as increased porosity or deformed grain structures were observed, which verifies the minor volume changes inferred from the effective stress path. 1. INTRODUCTION Anisotropic rocks play an important role for engineering applications in the subsurface. Transversal isotropy is commonly associated with layered sedimentary or metamorphic rock such as sand- and siltstones, mud- or clay rocks, shales, slates and schists. Clay-rich rocks are currently investigated for their application as geological barriers in nuclear waste repositories in many countries (e.g. Belgium, Canada, France, Germany, Japan, Switzerland, United Kingdom and the United States). The hydro-mechanical response around a repository tunnel during and after the excavation is influenced by the anisotropy of the rock. The anisotropy ratio, i.e., the ratio between rock properties parallel and normal to the plane of transversal isotropy, has been investigated in a variety of experimental studies (e.g. Wild and Amann, 2018; Minardi et al., 2021). However, these two endmember orientations, i.e., 0° and 90° between the loading direction and the plane of anisotropy, cover only a minor portion of geometrical constellations around the full tunnel circumference (Fig. 1.). For the majority of geometric constellations the plane of structural anisotropy, i.e., the bedding or foliation, is oblique to the tangential stress orientation. Favorable boundary conditions for a nuclear waste repository include tectonically-inactive sites, where the bedding is oriented (sub-)horizontally and the major principle stresses are oriented vertically and horizontally. Fig. 1. shows the anticipated geometric constellation in a sub-horizontal layered clay shale at large depth. Although stress rotation may take place during excavation, this simplified sketch suggests that the two endmember constellations, where maximum load is oriented parallel (P-configuration) and perpendicular (S-configuration) to the plane of anisotropy, are limited at the roof/top and the side walls of the tunnel, respectively. All other constellations represent an oblique orientation of the tangential stress in respect to the bedding plane orientation (further referred to as Z-configuration).
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,001 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».