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The shear strength of concrete-rock interface is a key factor to evaluate the stability of gravity dams. The shear strength assessment by achieving tests on small samples gives values different from those estimated by back-analysis on the existing dams. This work aims to study the shear behaviour of concrete-rock interface in the metric scale. Five direct shear tests were performed on bonded meterscale concrete-granite interfaces in the range of normal stresses to which gravity dam foundation is subjected. Specific instrumentation were installed to monitor the failure mechanisms during the tests. The five concrete-rock interfaces have not broken by shearing of materials (concrete, rock) in the shear plane imposed by the test device, but by debonding of the contact between concrete and rock. Considering roughness of the contact surface in the decimeter scale and the results of shear tests carried out in the same scale, the decimeter scale is demonstrated to correspond to the elementary surface for the shear behaviour of the metric concrete-rock interface. According to the level of normal stress, the stiffness of both materials and the main asperities in the decimeter scale, different failure mechanisms occur locally to justify the overall failure in the metric scale.

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The shear strength of concrete-rock interface is a key factor to evaluate the stability of gravity dams. The shear strength assessment by achieving tests on small samples gives values different from those estimated by back-analysis on the existing dams. This work aims to study the shear behaviour of concrete-rock interface in the metric scale. Five direct shear tests were performed on bonded meterscale concrete-granite interfaces in the range of normal stresses to which gravity dam foundation is subjected. Specific instrumentation were installed to monitor the failure mechanisms during the tests. The five concrete-rock interfaces have not broken by shearing of materials (concrete, rock) in the shear plane imposed by the test device, but by debonding of the contact between concrete and rock. Considering roughness of the contact surface in the decimeter scale and the results of shear tests carried out in the same scale, the decimeter scale is demonstrated to correspond to the elementary surface for the shear behaviour of the metric concrete-rock interface. According to the level of normal stress, the stiffness of both materials and the main asperities in the decimeter scale, different failure mechanisms occur locally to justify the overall failure in the metric scale.

Développé en France dans les années 1970, le clouage des sols est une technique de stabilisation des talus réalisés par déblai. Des inclusions subhorizontales assurent la stabilité de l’ouvrage par frottement avec le sol. Les réflexions engagées à l’occasion de la révision en cours de la norme NF P 94-270, sur le dimensionnement des massifs en sol renforcé, ont souligné le manque de connaissances quant aux efforts au parement, notamment sur l’influence du phasage de construction sur ces efforts. Afin de mener une étude paramétrique pour répondre à ces questions, des modèles réduits de paroi clouée ont été réalisés et instrumentés, puis centrifugés à l’Université Gustave Eiffel, campus de Nantes. Un protocole expérimental spécifique a été utilisé pour réaliser l’excavation en vol. Les évolutions des efforts le long des clous ont été mesurées à l’aide de fibres optiques équipées de réseaux de Bragg. Enfin, les déplacements du massif ont été observés à l’aide d’une technique d’imagerie appelée GeoPIV, les modèles centrifugés étant réalisés dans un caisson à face latérale transparente. L’élancement du massif cloué, (rapport entre hauteur du mur et longueur des clous) a une forte influence sur le comportement de l’ouvrage et en particulier sur la répartition des efforts au parement. La technique de GeoPIV a permis en outre de décrire les mécanismes de rupture des différents soutènements par clouage testés dans cette étude.

A new concept for constructing the facing of soil nailed walls is proposed and validated through experimental and numerical approaches. This new process uses precast concrete panels. For each excavation step, the soil reinforcements are first connected to the panels. A slightly cemented 4-6 mm crushed stone is then injected, through the weep holes, between the panels and the excavation vertical cut, applying a confining pressure to the ground and providing continuous high capacity drainage behind the facing. The structural design of the precast reinforced concrete panel, based on full scale loading tests in the laboratory and nonlinear numerical simulations, are presented in detail. Crack initiation and failure modes are properly predicted by the model. A full-scale experimental soil nailed wall 7.5 m high was also built to evaluate the environmental, economic and mechanical performances of the new construction technique compared to the conventional shotcrete technique. The new construction technique greatly improves worker's safety, significantly reduces construction duration and cost and improves the mechanical behavior of the soil nailing technique and drainage of the facing. Compared to the conventional shotcrete technique, the new technique reduces concrete consumption by 64% and greenhouse gases emission by 56%.

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