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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.

The Callovo-Oxfordian claystones were chosen for their low permeability. This feature marked by the clay content of the rock is inevitably accompanied by a low tensile strength. This generates the development of an excavation damaged zone. Seismic elastic wave propagation analysis methods are potentially valuable for the characterization of the damaged zone. These methods are more or less adapted to clay environment mainly due to the strong wave attenuation. The easiest seismic method to implement is probably the seismic refraction. It is used from the surface of the wall. It involves analyzing the waves refracted at the interface between the fractured zone and the bedrock. Sato et al. (2003) showed with this method the influence of excavation mode on the extension of the damaged zone in the underground laboratory in Japan Tono (sedimentary clay rock). Similarly, Lagarde et al. (2006) used the method in the Callovo-Oxfordian claystone. The application of seismic refraction in this context is at the limit of resolution because it assumes a multilayer tabular model without velocity reverse and the error on the arrival time measured is very close to time variations due to the damaged zone. The analysis of the surface waves is based on the dispersive property of these waves. They have the particularity to propagate at different depths depending on their frequency. The objective is therefore to measure the dispersion curve of the wave model and find the velocity profile that best matches. This method called MASW (Multi-Channel Acquisition of Surface Waves) is typically used to find the velocity profile of a tabular field where the inversion is simplified. As part of the thesis of Lagarde (2007), the MASW method was extended to the concave geometry of deep underground excavations to characterize the velocity profile in the damaged zone. It makes it possible to reveal any velocity profile including those with one or more velocity reverse. This method was used at the Meuse Haute Marne URL to characterize the damaged zone at the bottom of a drift. Seismic methods can also be implemented in borehole, for example ultrasonic logs. They are well suited to the scale of the damaged zone and numerous surveys in deep underground excavations. In the Meuse Haute Marne URL, this method has been used on numerous occasions (Schuster et al, 2001) during the different phases of the excavation of shafts and galleries. These velocity measurements are used to describe both the evolution of the gradient of damage / deconfinement from gallery wall and isolated fractures at greater depth. Acoustic emissions (AE) occur during initiation and expansion of cracks. Quantifying and locating those AE can bring information in determining the initiation and expansion of the damaged zone. Monitoring these AE has been successfully applied around structures in very resistant rock under high stresses such as granite host rocks of the Lac du Bonnet, Manitoba (Meglis et al, 2005). In claystones, however, the strong wave attenuation make them almost undetectable. The only opportunity to detect them is to place acoustic sensors in close proximity to sources. Forney (1999) developed a compact device capable of recording AE reflecting the creation of the damaged zone during the excavation of a gallery in Mont Terri. Claystones might show a natural variability that must be taken into account in the analysis of velocity variations induced by damage. A solution to overcome this problem is to measure the velocity of the waves in the rock before it was damaged and monitor its evolution during the excavation of the build. This technique called "velocity survey" has been implemented several times during the excavation of shafts (Balland et al, 2009), galleries or slots. It allowed characterizing the intensity and extension of the damaged zone, as well as the phenomena occurring during sealing or reconfinement of a fractured rock vicinity. Using a specifically designed 3D device with S and P waves back analysis in the stiffness matrix changes.

Imaging tectonic faults with small vertical offsets in argilittes (clay-rock) using geophysical methods is challenging. In the context of deep radioactive waste disposals, the presence of such faults has to be assessed since they can modify the rock confining properties. In the Tournemire Experimental Platform (TEP, France), fault zones with small vertical offsets and complex shape have been identified from underground works. However, 3D high-resolution surface seismic methods have shown limitations in this context that led us to consider the detection and characterization of the faults directly from underground works. We investigate here the potential of seismic full waveform inversion (FWI) applied in a transmission configuration to image the clay-rock medium in a horizontal plane between galleries, and compare it with first-arrival traveltime tomography (FATT). Our objective is to characterize seismic velocities of a block of argilittes crossed by a subvertical fault zone with a small vertical offset. The specific measurement configuration allows us to neglect the influence of the galleries on the wave propagation and to simplify the problem by considering a 2D isotropic horizontal imaging domain. Our FWI scheme relies on a robust adaptation of early-arrival waveform tomography. The results obtained with FATT and FWI are in accordance and both correlate with the geological observations from the gallery walls and boreholes. We show that even though various simplifications are done in the inversion scheme and only a part of the data is used, FWI allows to get higher resolution images than FATT, and is especially less sensitive to the incomplete illumination as it uses also diffracted energy. The results provided in this study highlight the complexity of the fault zone, showing a complex interaction of the main fault system with a secondary system composed of decimetric fractures associated with the presence of water.

Recent advances in seismic inversion methods allow us to get high-resolution quantitative representations of mechanical parameters of the Earth. One of the most promising inversion method is the Full-waveform inversion (FWI) method which basically consists of an iterative data fitting process based on a local optimisation (Tarantola, 1984) and unlike conventional methods (e.g. first arrival times tomography) all the information available in the data can be handled. This method has been first applied to depth exploration (Virieux and Operto, 2009), but some authors already applied it to quantitatively image the near-surface. For example, G'elis (2005) succeeded to image cavities using synthetic data including surface waves arrivals. However one of the most important remaining challenges is the validation of the method with real field data that presents many difficulties: field data are often measured on not well-known media composed of high heterogeneity degree, important intrinsic attenuation and with prominent three dimensional effects. Considering all these difficulties, the necessity to have an experimental intermediate validation step becomes obvious. The aim is to reproduce the field experiments in a well-controlled environment at a smaller scale using a well-defined spacio-temporal scalling. The physical reduced scale modeling has several advantages compared to field-measurements: first the model physical parameters are well controlled, thus numerically repeatable; secondly, the great flexibility of the setup enables to experiment easily novel measurement configurations. This validation approach has already been first applied for geophysical imaging purposes by French (1974). Recently Bretaudeau (2010) designed an ultrasonic measurement bench called MUSC with several features that enable an excellent reproducibility of field measurements from the surface. For instance, a special attention has been paid to select a source that can be assimilated to a point source and the sensors displacements are controlled with an accuracy of 10 m. Using this experimental setup, Bretaudeau (2010) showed promising results on the inversion using the vertical component. Due to recent technological improvements (Blum et al., 2010), it is now possible to record the vertical and the horizontal components simultaneously using a new laser interferometer device which has been implemented in the MUSC measurement bench. In this context, the aim of the study presented here is to investigate numerically the benefits of the each component in the frame of the FWI method and to present the recent advances on measurements of both components on reduced physical scale models. First, the physical reduced scale model and its numerical representation will be described, then a numerical study will present the benefits provided by each component for velocities reconstructions and finally measurements of the vertical and horizontal components on the reduced physical scale model will be presented and compared to numerical simulations.

Cet article vise à utiliser les ondes de Rayleigh qui précèdent le passage de trains à grande vitesse (TGV) pour détecter des cavités souterraines dans un sol limoneux. Tout d'abord, des résultats de simulation montrent que la présence d'une cavité produit un effet de filtrage sur le spectre des ondes de Rayleigh dans une gamme de longueur d'onde en relation avec sa profondeur. Ensuite, l'article présente les résultats d'une campagne expérimentale menée sur un site-test, à partir de l'analyse des signaux sismiques précédant le passage du TGV. Les résultats mettent en évidence une variation de 3 à 6 dB d'amplitude dans un voisinage de 10 m de l'axe des cavités, pour des longueurs d'ondes de 8 à 20 m. Enfin, l'analyse du bruit ambiant conduit à une observation similaire pour de plus grandes longueurs d'onde.

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.

In this paper the propagation of surfaces waves is investigated in the case of seismic measurements recorded along the circumference of concave structures. The underlying objective is to recover non destructively the mechanical properties of material from multiple channel analysis of surface waves measurements. This experimental configuration along the circumference is unavoidable in the case of concrete circular tunnels or shafts when the sensors cannot be installed along the structure base line. For surface waves it is shown that the influence of the curvature has a major impact on its phase velocity which cannot be incorporated in classical multiple channel analysis of surface waves forward problem. Consequently, we have developed a numerical model dedicated to such geometry that relies on complex values of the surface waves phase velocity. This model is confronted with experimental data recorded on a reduced scale concrete tunnel of metric size. The agreement between experimental and numerical shall be the basis of an in situ non destructive testing technique

Lors du creusement de galeries profondes ou de tunnels, les propriétés hydromécaniques de la roche encaissante autour de l'ouvrage sont altérées sur une certaine distance qui dépend de la nature de la roche et du type d'excavation. Une telle zone est appelée Excavation Damaged Zone (EDZ). Cette altération de l'encaissant se caractérise par une densification de la fracturation intrinsèque de la roche. La connaissance des caractéristiques mécaniques de l'EDZ ainsi que son extension est actuellement un axe majeur de recherche notamment pour la conception de centres de stockage souterrains des déchets nucléaires. En effet, l'EDZ, par son réseau de fractures, est considéré comme un chemin potentiel pour les radionucléides et donc comme un facteur de possible contamination du milieu. Les méthodes géophysiques initialement utilisées à des échelles kilométriques pour analyser les événements géologiques, sont dorénavant transposées à des échelles métriques voire centimétriques et appliquées en génie civil ou dans tout autre domaine de l'ingénierie. L'intérêt de telles méthodes est leur caractère non destructif qui les rend faciles d'utilisation et généralement moins coûteuses que d'autres méthodes destructives. Elles permettent aussi un suivi dans le temps de l'évolution des propriétés des matériaux auscultés. La MASW (Multiple Acquisition of Surface Wave) est une méthode géophysique utilisant le principe de dispersion des ondes de surface (Park et al, 1999). Cette méthode a été transposée dans ce contexte afin d'obtenir un profil 1D des vitesses des ondes de cisaillement (S) autour d'un ouvrage souterrain et ainsi de déterminer l'extension et les caractéristiques en terme de vitesse des ondes S de l'EDZ. L'intérêt de cette méthode est sa facilité de mise en oeuvre et la possibilité de l'utiliser sans restriction majeure.

A new tomographical technique is introduced : a Pseudo-Ray Iterative Averaging Method. It is a geometrical method. During the inversion process, influence zones are defined. Their size is chosen a priori, under physical considerations. This technique transforms the process into an inversion method without blocks. For each zone,weighting factors are defined in order to discriminate between the rays as well as between the zones. The ray tracing is analytical. The combination of these techniques produces a very small computing time consuming method. It's possible to add to the process, evaluations of the resolution and the error as it is made for the matricial case. For civil engineering, several applications are described. Celerity or Q- factor tomographies are computed from measurements of travel times, rise- times or amplitudes. Special devices have been designed in arder to minimize the field data acquisition lime., Une nouvelle méthode de tomographie est décrite (PRIAM~2D). C'est une méthode géométrique itérative. Au cours de l'inversion, des zones d'influence sont définies pour chacune des cases prises en compte. La taille de ces zones est choisie a priori (à partir de considérations physiques). Leur existence transforme la méthode géométrique en une technique d'inversion sans blocs. Le calcul au sein de chacune des zones comporte des pondérations visant à discriminer les rais entre eux. Celles- ci permettent également de discriminer certaines parties de l'image les autorisant ainsi à varier plus librement que d'autres. Les rais utilisés sont analytiques. Des évaluations de la résolution et des erreurs sont introduites. Ces techniques permettent d'obtenir des résultats comparables à ceux fournis par des méthodes matricielles tout en conservant des temps de calcul nettement inférieurs. Dans le domaine du Génie Civil plusieurs applications sont envisagées. Des sols, ainsi que certaines parties d'ouvrages d'Art, peuvent être auscultés. Il est possible d'obtenir des cartes de la vitesse des ondes de compression ou du facteur de qualité, à partir de mesures de durées de propagation, de temps de montée ou d'amplitudes. En outre, Une chaine de mesure spéciale a été mise au point de manière à minimiser le temps de la mesure.

Les récentes applications des théories de l'inversion à la physique du Globe ont été adaptées à l'échelle du Génie-Civil. Des mesures de durées de propagation entre puits permettent d'obtenir la répartition des vitesses sismiques dans le plan contenant les deux forages. Le problème de l'inversion en facteur de quaiité peut se poser dans les mêmes termes que ceux de l'inversion en vitesse. Des mesures d'amplitude~ permettent d'obtenir la répartition des facteurs de qualité. La mise au point des programmes d'inversion a nécessité une élaboration préalable de programmes de simulation. Les données synthétiques obtenues ont permis de juger de l'influence des divers paramètres sur les résultats des inversions ainsi que de tester les critères de contrôle des résultats. Par la suite, un matériel spécifique a été mis au point afin d'obtenir des données réelles. Les géométries des premières Images calculées, en vitesse et en facteur de qualité sont identiques. Ceci apporte une crédibilité importante aux résultats de l'inversion en facteur de qualité. L'application particulière décrite ici est le contrôle des injections. Des mesures identiques avant et après injection ont permis de déterminer clairement les conséquences diverses de l'injection dans les sous-sols étudiés., pas de résumé