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La teneur en eau est un paramètre conditionnant le développement des dégradations des structures en béton armé telles que la corrosion des armatures. Afin de surveiller le profil de teneur en eau sur une grande épaisseur d'une structure en béton, un capteur multi-électrodes permettant la mesure de la résistivité électrique est développé dans cet article. Un capteur en forme d’anneau, conçu en circuit imprimé, placé à une profondeur donnée, a l'avantage de moyenner plusieurs points de mesure entre les électrodes à cette profondeur, et ainsi d'intégrer l'effet de la variabilité naturelle de la résistivité donc de la teneur en eau. Des validations expérimentales utilisant des solutions salines de conductivité connue ainsi que des éprouvettes de béton soumises au séchage sont étudiées pour valider la réponse du capteur en utilisant différents points de mesure. Les résultats démontrent la capacité du capteur proposé à surveiller les profils de résistivité dans le béton en intégrant la variabilité latérale du matériau., Academic Journal of Civil Engineering, Vol 38 No 2 (2021): Special Issue - Diagnobéton 2021

International audience; Dike management has become a major concern in France over the last 20 years, after several major flood disasters caused by river and sea dikes failures. These events, the poor state of more than 60% of the dikes in the country, and the ever-growing threat of floods occurrence increase due to global climate change, have only made obvious the need for dikes reinforcement and for their tighter surveillance. Today, the most commonly used method for both routine and crisis monitoring of dikes is based on visual inspections by field operators. It allows precise detection of most of the surface indicators (i.e animal burrows, structural deformations, topographic anomalies, water seepage, etc.) resulting from disorders affecting these structures. However, this method is time consuming when long sections of dikes are inspected and is not entirely safe for the field operators during a flood. The DIDRO (DIke monitoring by DROnes) project aims at developing a solution for high efficiency routine and crisis monitoring of dikes using a UAV system carrying multiple remote sensing sensors and aquatic measurements equipment. Remote sensing sensors include LiDAR, thermal infrared, near-infrared and visible image sensors, and provide very high resolution data of the surface of the dike. Such very high resolution sensors, which have never been combined so far on a UAV for this type of survey, allow precise detection of a large number of surface indicators of internal and external dike disorders. They can be implemented for both routine and crisis monitoring. Aquatic measurements consist in flow velocity estimations using floating targets dropped in the river or in the sea by the UAV and in a system for water turbidity estimation towed by the UAV. This system is particularly useful for the detection of signs of dike materials erosion during a flood. Also, geophysical methods having proved efficient at providing information on the internal state of dikes, it has been considered very useful to integrate geophysical equipment to the UAV system. Geophysical measurements are conducted using electrical resistivity tomography, self potential and background seismic noise equipment. The UAV is then used to tow or to drop the equipment along the dike and to remotely collect data generated by devices manually positioned. This can be particularly useful during flooding, when accessing the dike may be dangerous. The switch from one payload configuration to another is made easy by a specific mounting system, adaptable to different types of UAV. This makes the DIDRO solution more easily deployable during flooding events. This presentation will focus on the description of the different payload configurations of DIDRO and on the specifications of the equipment used, and will present some results obtained during tests carried out on several dikes in France.

BELIEF 2018, 5th International Conference, COMPIEGNE, FRANCE, 17-/09/2018 - 21/09/2018; We propose the use of Smets and PCR5 rules to merge artificial geophysical and geotechnical data, as part of fluvial levee assessment. It highlights the ability to characterize the presence of interfaces and a geological anomaly.

23rd European Meeting of Environmental and Engineering Geophysics, MALMÖ, SUEDE, 03-/09/2017 - 07/09/2017; In this study, we introduce a new database framework for levee investigation. We are considering on an equal footing geophysical and geotechnical investigation methods in order to assist the agencies and levee managers in selecting the most relevant methods for the levees' characterization. For this to be possible, we are taking into account the environmental constraints, the pathologies and the failure modes of the levees. The other aspect of this work is to open new ways of reflection in the research community with an important bibliographic work being carried out. We first focus on the relations between pathological physical properties and failure modes of a levee in order to identify which properties and characteristics of a levee need to be estimated. Then, we display our new database framework using the example of the Electrical Resistivity Tomography method. This work finally insists on the benefits of such a structure to propose new method investigation combinations and to provide a significant quantity of references for the research community.

NDT-CE 2015, International Symposium Non-Destructive Testing in Civil Engineering , BERLIN, ALLEMAGNE, 15-/09/2015 - 17/09/2015; Maintenance and inspection of concrete structures are increasingly important issues considering the high number of aging structures and infrastructures. Non-destructive techniques (NDT) are fast and allow monitoring the structure during all of its life service. NDT are sensitive to various concrete properties, among which is water content. This latter is a significant parameter of concrete pathologies, an accurate estimation of its value is therefore important. Our research focuses on two NDT: capacitive and electrical probes, both of which are highly sensitive to water content. By varying the size and the spacing of the electrodes of both devices, we attain multiple investigation depths and obtain raw integrated measurements from the studied structure surface. An inversion procedure is then applied to the raw data to obtain profiles in the concrete. Electrical resistivity tomography was obtained using commercial software, while for capacitive NDT an original inversion procedure was developed. After calibration, the two NDT allow the determination of quantitative water saturation degree profiles into concrete. The aims of this paper are to present the two easurement and inversion procedures and to validate them on concrete slabs submitted to an imbibition process and controlled by reference methods.

Direct Current (DC) electrical resistivity and dielectric permittivity are material properties well known to be sensitive to various aspects of concrete condition related to corrosion risk. A co-axial electromagnetic (EM) cell for the measurement of frequency dependent complex permittivity of concrete cores was developed by IFSTTAR in 2005. This paper describes the subsequent development of a multi-ring electrical resistivity cell for the evaluation of concrete cores of a geometry equivalent to that of the EM-cell in controlled laboratory conditions. The multi-ring resistivity cell presented here is capable of identifying resistivity gradients over the height of the investigated sample. The homogeneity of the sample can therefore be verified as it is an important requirement for obtaining reliable results. Also described in this paper, is the development of a multi-electrode resistivity surface probe for in-situ measurements and capable of performing ERT in order to cross-correlate laboratory results with those from real concrete structures.The paper focuses on the development of these two resistivity devices, and the numerical modelisation, calibration, validation and cross-correlation thereof.The development of the resistivity cell will enable future work to establish master curves relating permittivity and DC-resistivity to parameters indicative of concrete condition (particularly water and chloride content, porosity and hydraulic permeability). The final aim is then to estimate these parameters for on-site applications from responses of electromagnetic non-destructive evaluation (NDE) techniques such as Electrical Resistivity Tomography (ERT), Capacitive Method and Ground Penetrating Radar (GPR).

In geotechnical engineering, there is a need for a technique to measure in-place density and water content of soil quickly, precisely, and preferably, in a non-destructive manner. Combined traditional electric and electromagnetic methods could answer to this need : they are used in this study to determine the relationships of electrical conductivity and dielectrical permittivity versus hydric properties of loamy sand on a density and moisture controlled site. This plurimetric experimental site is composed of three basins of the same material. Each basin is at one soil water content and composed of several parts compacted at different dry densities. Previous laboratory studies showed that electrical conductivity and dielectrical permittivity increase with the increase of dry density and with the increase of gravimetric water content. The aim of this study is to compare laboratory and in-situ measurement data in order to obtain a model useable on site.

In geotechnical engineering, there is a need for efficient techniques which could measure soil density and moisture content, volume integrating and in a non-destructive manner. Electrical resistivity and dielectric permittivity depend on both these soil parameters and it is hoped that these properties could help addressing this geotechnical issue. In order to evaluate this possibility, the influence of water content and dry density of a compacted finegrained soil on its resistivity and its permittivity is being studied. As suggested by previously published models and experimental data, electrical resistivity decreases when dry density or gravimetric water content increases, and dielectric permittivity increases with an increase of water content or dry density. The influence of water content is the most significant on permittivity whereas both dry density and water content have a significant influence on resistivity.

The French Public Works Research Laboratory and the Road Experimentation Center of Rouen installed an experimental embankment dam in order to monitor during long term geotechnical behaviour and more specifically electrical resistivity of the soil materials. The purpose is to evaluate water content evolution in the embankment dams made of fine compacted soil. Moreover a multitude of instruments were installed to survey water content, temperature, horizontal and vertical displacement in the engineering structure. Additional laboratory experiments on soil samples from the dam, permitted to identify the influence of temperature, water content and density on the measured electrical resistivity. By combining the field and the laboratory measurements, a model is developed, which corrects the measured resitivities to a reference temperature. Thus we are able to obtain a true resistivity section and convert it to a gravimetric water content section.

Fluvial and coastal dikes are the primary protection for human life from natural hazards like flooding or wave action. To build these hydraulic earthworks requires many materials with specific performances in terms of workability, mechanical strength, permeability, resistance to erosion, etc. Very often, local material does not meet requirements imposed by standards, and the transportation of material over long distances is only a short-term solution from an environmental point of view. Lime is used for construction purposes because it decreases the plasticity index and water content of soil, which facilitates compaction and improves its mechanical performance over time. However, the resistance to erosion of lime-treated earthwork remains little known and this is one of the reasons why lime has not been applied to dikes yet. The engineering behavior of lime-treated dikes depends on the lime-soil interaction and environmental impacts. This study focuses on the comparison between raw and treated material behaviors regarding erosion processes and the effects of water. Erosion tests were carried out on two full-scale experimental dry dikes and laboratory samples for different curing times. Three types of tests were performed: Mobile Jet Erosion Test (an apparatus that can be used either in the laboratory or in the field), Hole Erosion Test (an efficient and convenient laboratory apparatus) and Enhanced Crumb Test (an evolution of the ASTM Crumb Test). In all configurations (soil and apparatus), this study reports a great increase in the resistance to erosion of the treated materials, which leads to a significant reduction in the risk of both internal and surface erosion of earthworks. Last, we discuss the application of these materials for building coastal dikes (characterization of the sustainability of lime treated soil versus saline environment, wetting-drying cycles etc.), and the possible monitoring of such a full-scale coastal dike by geophysical methods.