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The depoldering of Hedwige-Prosperpolder offers a 6 km2 Living Lab environment, where current and innovative techniques, processes, methods and products were tested for practical validation. Many experiments, like overtopping tests, wave run up tests, erosion tests, etc. have been carried out on the levee to increase our knowledge on flood resilience. Knowledge about the dike construction and layering of the subsoil is essential for flood risk analyses. The living lab Hedwige Prosperpolder offered the ideal opportunity for testing various techniques to determine the layered structure of levees.This has led to geophysical and geotechnical surveys to be carried out at the Living Lab Hedwige Prosper Polder (LLHPP), near Antwerp (Belgium). The studied dike crosses the Belgium-Dutch border along the banks of the river Scheldt.Several CPT’s and a number of drillings have been performed on the dike crest by the Geotechnics Division of the Department of Mobility and Public Works (MOW) from the Flemish Government in the period 2019-2021. Monitoring wells were installed through the dike, registering the ground water level continuously. Ground samples were analyzed in the geotechnical laboratory in order to characterize the dike composition. All the results of these tests have been reported in De Backer & D’heer, 2022 and Elgün & De Backer et al., 2019. Classical Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) profiles were performed alongside the dike as well as across the dike. At some specific positions, drilling with the Permeafor testing were realized to characterize the soil permeability. These tests have been performed by Cerema between 5th and 9th October 2020.This report aims to present the interpreted results of the various geophysical and geotechnical techniques and to discuss the effectiveness of the techniques for determining the location of various soil layers in levees. All results are cross-analyzed to assess the dike conditions. In order to better visualize the results, an existing Digital Elevation Model (DEM) is used to insert the geotechnical and geophysical data in. The 3D visualization provides an accurate overview of dike materials, constituting the basement of future experiments of the Polder2C’s project. This work has also been compared with the above mentioned geotechnical survey by MOW and a former geophysical survey performed by Fugro (Elgün, 2019 and Elgün & De Backer et al. 2019) one year before.A part of this work has been presented in June 2021 at the International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences (Antoine et al., 2021).

Usuellement, la mesure par séchage en étuve et la mesure de la masse volumique humide par méthode nucléaire permettent de relier la teneur en eau massique à la teneur en eau volumique. La méthodologie étudiée ici propose d'associer à la mesure de la masse volumique humide une estimation de la teneur en eau volumique par des méthodes électromagnétiques via la mesure de la permittivité diélectrique apparente du sol. Ce paramètre physique peut être relié à la teneur en eau volumique par une loi empirique ou par une loi de mélange, dans laquelle la permittivité et la concentration volumique de chaque constituant, notamment celle de l'eau, sont prises en compte. Deux méthodes électromagnétiques sont utilisées pour déterminer la permittivité apparente du sol : la première est basée sur la mesure des paramètres de réflexion d'un monopôle quart d'onde enfoncé dans le matériau étudié. La seconde est le radar impulsionnel qui repose sur le principe de la propagation des ondes électromagnétiques à travers une épaisseur donnée de matériau. Ces méthodes permettent d'estimer directement et in situ la teneur en eau volumique. Les résultats obtenus selon les deux méthodologies sont comparés et critiqués. Des améliorations notables sont préconisées pour de futures recherches.