Rock joints submitted to direct shear tests under low normal stress: evaluation of apparent cohesion values and key parameters

Adrien Rullière, Patrice Rivard, Laurent Peyras, Pierre Breul

In the proceedings of: GeoEdmonton 2018: 71st Canadian Geotechnical Conference; 13th joint with IAH-CNC

Session: Rock Mechanics and Engineering Geology I

ABSTRACT: Shear behavior 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 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).

RÉSUMÉ: Le comportement au cisaillement des joints rocheux est influencé par la rugosité du joint et de nombreux modèles de ésion entre les épontes. Cependant en pratique, les règlements professionnels du génie civil proposent le modèle de Mohr-Coulomb (M-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 est autorisée avec le critère de M-C. nt direct sur des répliques naturelles de à de faibles contraintes normales (0.1 à 1MPa), les résultats montrent que plus le JRC de Barton est élevé pour une cohésion apparente de 80kPa contre près de 470kPa pour une discontinuité de JRC 18.6.

Please include this code when submitting a data update: GEO2018_229

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