Rock joints submitted to direct shear tests under low normal stress: evaluation of apparent cohesion values and key parameters
Bibliographic record
Abstract
Shear behaviour of rock joints is governed by joint surface roughness and many theoretical criteria have been developed over decades that consider the rock joint conditions and a potential value for the cohesion between both walls of the joint. However, in practice, most of civil engineering guidelines are still suggesting to use the Mohr-Coulomb (M-C) friction criterion that relies on a friction angle and a cohesion values determined from lab test or literature. For unbounded rough rock joints, no true cohesion can be considered since walls are not physically linked. Yet, a value of apparent cohesion, resulting from joint roughness and interlocking conditions is authorized to be used with M-C. But currently, no consensus exists to set or evaluate the apparent cohesion to consider. That is why a direct-shear test experimental program based on natural rock replicas was developed to investigate the roughness effect on apparent cohesion. For a joint submitted to low normal stress range conditions (0.1 to 1MPa), results show that higher Barton's JRC is and more the apparent cohesion value associated is high: a joint with a JRC of 8.9 shows an apparent cohesion value of 80kPa versus 470kPa for a rougher joint (JRC=18.6). / Le comportement au cisaillement des joints rocheux est influencé par la rugosité du joint et de nombreux modèles de résistance au cisaillement ont été développés, prenant en considération l'état de la discontinuité et l'existence ou non d'une valeur de cohésion entre les épontes. Cependant en pratique, les règlements professionnels du génie civil proposent le modèle de Mohr-Coulomb (M-C) en s'appuyant sur des valeurs de cohésion et d'angle de frottement issus d'essais expérimentaux ou de la littérature. Pour les joints rocheux rugueux non liés, aucune valeur de cohésion réelle ne peut être utilisée puisque les épontes du joint ne sont pas physiquement liées entre elles. Néanmoins, une valeur de cohésion apparente, issue de la rugosité de la discontinuité et de conditions d'emboîtement est autorisée avec le critère de M-C. Mais à l'heure actuelle, aucun consensus n'existe pour choisir et évaluer la valeur de cohésion apparente à prendre en compte. C'est pourquoi un programme expérimental d'essais de cisaillement direct sur des répliques naturelles de discontinuités a été développé pour évaluer l'effet de la rugosité sur la cohésion apparente. Pour une discontinuité soumise à de faibles contraintes normales (0.1 à 1MPa), les résultats montrent que plus le JRC de Barton est élevé pour une discontinuité et plus la cohésion apparente associée l'est : une discontinuité présentant un JRC de 8.9 résulte ainsi en une cohésion apparente de 80kPa contre près de 470kPa pour une discontinuité de JRC 18.6.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".