214 publications from this institution
No abstract is provided for this article.
In this study, we assessed induced polarization as potential non-destructive method for root detection in dike embankments. We used both laboratory and field experiment to describe the electrical signal with a focus on soil water content. Our objective was to determine in which hydric state of the soil, and related electrical properties, roots could be accurately discriminated. We hypothesized that preferential water zone absorption near the roots could, in some conditions, contribute to locate them. During the laboratory experiments, we compared the response of containers filled with the same homogeneous silty clay bare material, and without (A) or with freshly cut root (B) at different levels of soil water content. Resistivity and phase variations with soil water content indicated that it was preferable to work in dry conditions since the contrast was higher. Interactions and overlapping between polarization effects of both root and soil made it difficult to interpret first chargeability maps. This led us to study temporal-spatial variations by considering the dynamics of water absorption during a field experiment. High resolution time lapses images showed a correlation between root location and complex resistivity anomalies. Although these first results have to be confirmed by further measurements, induced polarization seems to add useful information to interpret anomalies produced by woody roots.
Cracks are always a serious concern in the stability analysis of gravity dams. One of the main reasons for the initiation of cracks is overflow. In most pr
The shear strength of joints is governed by surface morphology, including roughness and interlocking conditions. Several criteria have been developed in recent decades to assess shear behavior. However, most civil engineering guidelines suggest using the Mohr-Coulomb criterion to evaluate shear strength. The Mohr-Coulomb criterion relies on a friction angle and a cohesion value determined from laboratory tests, the literature, and the engineer's experience. Two distinct cohesion concepts can be considered: true cohesion, which is a bond between the walls of the joint, and apparent cohesion. Apparent cohesion is obtained by performing a linear regression for the experimental shear strengths obtained in the laboratory for a given normal load interval. For unbounded joints, true cohesion cannot be considered because the walls are not physically bonded. However, apparent cohesion, describing joint roughness, interlocking, and the conditions of the joint walls, can be used with the Mohr-Coulomb criterion. Civil engineering standards are cautious about the use of apparent cohesion during design, and guidelines often recommend considering a null or low value. In this article, we focus on the effects of surface morphology on apparent cohesion, to better appraise the relevance of taking apparent cohesion into account in the Mohr-Coulomb criterion. Direct shear tests were performed on four different rock joint replicas tested under low normal load conditions (0.1–1.0 MPa). The results showed that apparent cohesion increased with roughness. Results also showed that the interlocking and damage state of the joint wall surfaces play a key role in the apparent cohesion value. When the sample is damaged or poorly interlocked, apparent cohesion is significantly reduced.
Levees are large alignment works on which only imperfect information are usually available. In this particular context, a probability-based model is suggested for evaluating the levee performance, taking into account imperfect data in a probabilistic format. Such a model will implement subjective probabilities that have been elicited by expert assessment to evaluate all criteria and uncertainties thereof. Based on a deterministic model of multicriteria aggregation and using Monte Carlo simulations, this will ultimately help build probability distributions for the performance indicator and for each levee section. The benefit of this model is to determine how much an evaluation may be trusted and to help decide which technical actions should be taken to improve a levee section performance. Résumé: Les digues sont des ouvrages à grands linéaires pour lesquels on ne dispose généralement que d’informations imparfaites. Dans ce contexte, on propose un modèle probabiliste d’évaluation de la performance des digues permettant la prise en compte des données imparfaites sous format probabiliste. Ce modèle met en œuvre des probabilités subjectives élicitées par jugement expert pour l’évaluation des critères et de leurs incertitudes. Sur la base d’un modèle déterministe d’agrégation multicritère et au moyen de simulations de Monte Carlo, il permet au final de construire des distributions de probabilité pour l’indicateur de performance et pour chaque tronçon de digue. Ce modèle présente les avantages d’apprécier la confiance qui peut être accordée à une évaluation et de guider le choix des actions techniques pour améliorer la performance d’un tronçon de digue.
No abstract is provided for this article.
France comprises 10,000 km of river levees. Those levees show highly variable performances caused by the various types of design and construction, age, environment, loadings, and maintenance and repair works performed on them. Available information on levees also varies in quality and most often proves to be incomplete, uncertain, or imprecise. Based on this, a method for providing a quantitative evaluation of levee performance is suggested. Such a method, based on a multicriteria decision-making model and subjective probabilities, takes all available pieces of information into account—design, construction, visual inspections, and geophysical and geotechnical investigations—and reckons them with the level of uncertainty of the available data. This method provides decision-making support in identifying the least efficient sections and setting up investigation and maintenance programs.
No abstract is provided for this article.
Face aux enjeux de la décarbonation de la production d’énergie, de la résilience des territoires face aux impacts du changement climatique, et de la préservation de la biodiversité, il est essentiel d’explorer les solutions d’aménagements de réservoirs susceptibles de répondre à ces sujets. Les centrales photovoltaïques flottantes sur retenues de barrages répondent à cet objectif [7]. La France dispose d’un potentiel d’installation de centrales photovoltaïques flottantes important, et de nombreux projets émergent. Ces projets apparaissent, pour nombre d’entre eux, loin des standards de sécurité attendus vis-à-vis de la sécurité des barrages. Devant cette situation, le CFBR a créé un groupe de travail visant à produire des recommandations techniques pour les projets d’installation de centrales photovoltaïques flottantes sur les retenues de barrage, de manière à améliorer la qualité des projets tout en garantissant la sécurité des barrages. Cet article rend compte de la première phase de travail de ce groupe qui a établi une enquête de retour d’expérience des projets en cours et des manques pour la profession des centrales photovoltaïques flottantes et des barrages.
No abstract is provided for this article.
Cette communication presente une synthese des differentes cotes et crues de reference habituellement utilisees pour l’evaluation de la securite d’un ouvrage hydraulique, y compris dans le cas d’un barrage ecreteur de crues ou d’une digue de protection contre les inondations. Les discussions au sein du groupe de travail du CFBR consacre a la justification de la stabilite des barrages et les travaux de recherche menes au Cemagref dans le domaine de l’analyse de risques appliquee aux ouvrages hydrauliques montrent les limites de ces definitions et ouvrent de nouvelles perspectives. Des propositions sont donc faites pour clarifier la terminologie. Cela aboutit a privilegier la determination des cotes atteintes dans la retenue pour differents scenarios de crues. Au final, il apparait possible d’associer des probabilites d’occurrence au depassement de la cote de surete ou de la cote de danger de rupture, et parallelement de proposer des valeurs minimales cibles pour ces probabilites, en fonction des types d’ouvrages et de leur classe.
[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGE
No abstract is provided for this article.
No abstract is provided for this article.
