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.

<p>Energy geostructures are a very cost-effective geothermal solution to produce renewable energy for the heating and cooling needs of the buildings. Their principle is to attach heat exchange pipes to the reinforcing cages of geotechnical structures (foundations, retaining walls, …). Mechanical and thermal roles are assigned to the same structures in order to reduce the economic and ecological costs.</p><p>Perturbations of the temperature field induced in the soil by this technology are propagated through conduction, diffusion and advection along the water-flow, leading to thermo-hydro-mechanical interactions between neighbouring structures. The behaviour of downstream energy geostructures is affected by the presence of upstream ones. In order to achieve a smart management of the shallow geothermal development at the city scale, it is crucial to characterize these interactions and their influence on the thermal efficiency.</p><p>For this purpose, a group of nine energy piles has been studied in Sense-City, a mini city where a specific climate can be imposed and the underground water-flow can be controlled. The piles can be thermally activated separately and are equipped with optic fibre to monitor their temperature evolution through time. Different groundwater conditions were imposed and different combinations of activated piles were studied.</p><p>To extrapolate and upscale the results, a numerical model was developed with CESAR-LCPC, a FEM software. Challenged by the experimental observations, the numerical model allowed simulating more complex boundary conditions and thermal infrastructure configurations. Furthermore, numerical modelling are able to simulate a long term experiment and to predict potential multi-year thermal shift.</p><p>Using combination of experimental and numerical experiments, observations can be made on the positive or negative consequence of energy geostructures interactions.</p>

Since the 1980’s, shallow geothermal solutions have been developed whose principle is to attach heat exchange pipes to the reinforcing cages of geotechnical structures. These low energy solutions combining a structural and a thermal role allow the fulfilling of the heating and cooling needs of buildings for a very low carbon cost. Energy geostructures are often placed in a groundwater flow. On one hand, it is a good way to avoid any multiyear thermal shift since the heat excess or default is tempered through the advection. This advection creates a thermal plume and heat waves in the soil can interact with downstream structures whose behaviour can be affected. The understanding of these interactions is essential for a smart management of the shallow geothermal development at the city scale. To study these interactions, a group of nine energy piles has been studied in Sense City, a mini city where a specific climate can be imposed and the underground water flow can be controlled. A numerical hydraulic-thermal coupled model was developed with the FEM software CESAR-LCPC to extrapolate the results. The combination of experimental and numerical models provides helpful results for the definition of guidelines concerning the prevention of interactions.

For several decades, energy piles have been developed to extract heat from the ground by using foundation piles as heat exchangers. However, the thermal loading of these piles directly affects their mechanical behaviour. Centrifuge modelling of a thermally loaded pile group within a groundwater flow makes it possible to improve the understanding of the hydro-thermo-mechanical behaviour of this type of foundation. In this research groundwater flow was established in a centrifuge model to study an energy pile group. The focus of this study is to enhance the research on energy geo-structures such as foundations which are very often located in soil with seepage. The groundwater flow allows reducing the thermomechanical effects and therefore plays the role as a stress and deformation stabiliser in addition to favouring the thermal recharge of the soil.

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