Detection of Leakage Areas in an Earth Embankment from GPR Measurements and Permeability Logging

Ground penetrating radar (GPR) is a nondestructive method allowing the improvement of our knowledge of civil engineering structures. In particular, this method may be a nondestructive efficient tool for dike diagnosis and complete classical geotechnical methods. In this paper, we present GPR observations obtained on an earth embankment (crest and sloped paved revetment) in bad condition and located on the lateral canal of the Loire river (Saint Firmin, 80 km South East of Orléans). These measurements are combined with corings, visual inspection, and permeability logging performed with an updated drilling system, the Perméafor. This survey leads (i) to the detection of decompressed zones associated with leakage areas visible at the foot of the downstream slope and (ii) to the location of potentials voids underneath the paved revetment. This multidisciplinary approach complied with the dike inspection methodology proves its efficiency for the assessment of earth embankments

Methodology Applied to the Diagnosis and Monitoring of Dikes and Dams

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Implementation of an Embedded Sensor Based on Electrical Resistivity to Monitor Drying in Thick Concrete Structures

Electrical resistivity is a parameter sensitive to several properties of concrete, including water content, which is one of the key parameters governing concrete long-term durability. In this paper, the monitoring of the concrete water content profile throughout its entire thickness is discussed using an electrical approach as a measurement method. This is very relevant to applications requiring a centimeter resolution over a large thickness. The aim of this paper is to implement a multi-electrode embedded sensor in a concrete slab to determine the resistivity profile over concrete depth in order to monitor its drying. The sensor, designed as a printed circuit board (PCB), is integrated in two 30 cm thick concrete slabs. Different measurement configurations are presented. Following qualification in laboratory and controlled conditions, the study focuses on characterizing the sensor‘s response during the drying of the slabs. The results demonstrate the capability of the sensor to monitor concrete drying by measuring the resistivity profiles with a spatial centimetric resolution

Développement de l’imagerie de résistivité électrique pour la reconnaissance et la surveillance des ouvrages hydrauliques en terre

En France, EDF gère un important parc d’ouvrages hydrauliques en terre dédié à la production hydroélectrique, avec des enjeux économiques et sécuritaires conséquents. D’autres ouvrages à charge permanente sont présents sur le territoire, par exemple le grand linéaire de voies navigables (transport, tourisme). Du côté des digues "sèches" (digues de protection contre les inondations), 7500 km de digues protégeant plus de 15000 km2 de zones inondables où vivent 2 millions d’habitants sont recensés. Pour ces ouvrages particuliers, il n’y a pratiquement pas d’année sans rupture et plus de 70 incidents ont été recensés en 25 ans par le Comité Français des Grands Barrages. L’érosion interne et la surverse sont les principales causes de ruptures et d’incidents de levées, digues et barrages en France et dans le Monde. L’Imagerie de Résistivité Électrique (IRE) est une méthode d’imagerie très sensible aux paramètres d’état d’un sol : la nature du sol et son contenu argileux, sa teneur en eau et la salinité de l’eau, son état de compacité et sa température. Elle fait donc partie des méthodes pertinentes pour la reconnaissance et la surveillance des ouvrages hydrauliques en terre. Ainsi, elle est complémentaire de méthodes de reconnaissance à grand rendement (ex : Profilage par méthodes électromagnétique à basses fréquences) en offrant localement des images du corps de digue et de sa fondation. En surveillance, alors que les méthodes basées sur les Potentiels Spontanés ou les mesures de température par Fibre Optique sont particulièrement sensibles aux écoulements d’eau (donc aux fuites à travers le corps de digue), l’IRE peut contribuer à imager les variations des propriétés d’état dans le temps de la structure interne de l’ouvrage (phénomène évolutif d’infiltration combiné ou non à de l’érosion interne). Cependant, dans l’utilisation conventionnelle de l’IRE, le manque d’information provenant des mesures, ainsi que la mauvaise prise en charge de ces mesures et de l’information a priori, entraînent la formation d’artéfacts dans les résultats d’imagerie. Dans ce sens, de nouvelles démarches d’acquisition et d’inversion sont développées, intermédiaires entre les techniques plus classiques 2D et 3D. Ces nouvelles approches, dont le but est de tirer le meilleur compromis entre coût d’acquisition et robustesse (fiabilité) du modèle final sont le fruit du développement d’un problème direct par éléments finis et d’un algorithme d’inversion 3D de type Gauss-Newton. Enfin, des campagnes d’auscultations sur ouvrage semi-contrôlé et sur ouvrage réel ont été réalisées afin de confronter ces développements à la complexité de cas réelles. Ces études révèlent que la qualité de la reconstruction et la capacité d’interprétation peuvent être considérablement améliorées par l’utilisation des approches développées

A cost-effective 3D electrical resistivity imaging approach applied to dike Investigation

Although DC electrical resistivity imaging is widely applied to dike investigation, either rapid 2D or high-resolution 3D approaches fail to address actual needs. An intermediate electrical resistivity imaging approach referred to as ?3D-? is introduced in this paper. The methodology is based on existing tools, and it offers useful and sufficiently reliable 3D images of the investigated structure within a cost-effective and flexible procedure. The survey design, the model discretisation, and the thorough integration of a priori information are the main phases of this procedure. To demonstrate the benefits and limitations of this approach, it is applied to an existing stretch of embankment levee along the Loire River. A numerical study was carried out both on synthetic and real data to assess the 3D imaging capability of the approach and the influence of prior information on the inversion outputs. The important role of a priori information is shown to be even more essential here. The results demonstrate the efficiency and versatility of the 3D- approach for reliable and cost-effective investigations of long dikes

2D-ERT monitoring of soil moisture seasonal behaviour in a river levee: A case study

International audienceWe present a study of the seasonal behaviour of soil moisture in an old embankment levee by means of 2D DC-electrical resistivity tomography monitoring based on an embedded electrode installation.We were able to produce seasonal resistivity change models that are compensated for temperature effects using a seasonal temperature profile model. Time-lapse sections of percentage resistivity changes show spatial and temporal overall consistency with seasonal variations of soil temperature. Discrepancies are likely due to the pavement layer that is not well considered in the inversion process as well as to time-lapse inversion pitfalls. Furthermore, a detailed estimation of seasonal moisture content variations could not be given as an accurate calibration of the employed suction probes was not achievable.Nevertheless, the levee appears to have spatially consistent time variations in soil moisture, clearly influenced by both rainfall and water table and river levels. Future work on developing 3D acquisitions and adding embedded moisture content probes should prove effective to our monitoring design and give a more detailed understanding of the soil moisture seasonal behaviour in the studied stretch of levee

Mesure de la résistivité électrique par capteurs noyés pour évaluer les profils de teneur en eau dans le béton

International audienceLa 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

A new database structure guiding the combination of geophysical methods for levee investigation

23rd European Meeting of Environmental and Engineering Geophysics, MALMÖ, SUEDE, 03-/09/2017 - 07/09/2017In 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

Accelerated Aging of Embedded Electrical Resistivity Sensor for Monitoring Concrete Structures

International audienc

Integration of geotechnical and geophysical techniques for the characterization of a small earth-filled canal dyke and the localization of water leakage

This paper investigates the combined use of extensive geotechnical, hydrogeological and geophysical techniques to assess a small earth dyke with a permanent hydraulic head, namely a canal embankment. The experimental site was chosen because of known issues regarding internal erosion and piping phenomena. Two leakages were visually located following the emptying of the canal prior to remediation works. The results showed a good agreement between the geophysical imaging techniques (Electrical Resistivity Tomography, P- and SH-waves Tomography) and the geotechnical data to detect the depth to the bedrock and its lateral variations. It appeared that surface waves might not be fully adapted for dyke investigation because of the particular geometry of the studied dyke, non-respectful of the 1D assumption, and which induced depth and velocity discrepancies retrieved from Rayleigh and Love waves inversion. The use of these classical prospecting techniques however did not allow to directly locate the two leakages within the studied earth dyke. The analysis of ambient vibration time series with a modified beam-forming algorithm allowed to localize the most energetic water flow prior to remediation works. It was not possible to detect the leakage after remediation works, suggesting that they efficiently contributed to significantly reduce the water flow. The second leakage was not detected probably because of a non-turbulent water flow, generating few energetic vibrations