Leakages of reservoirs are responsible for the loss of water resources and the spread of contaminants. We develop a methodology to detect leaks located at the bottom side of a reservoir with the minimally invasive mise-à-la-masse method, which involves the potential electrodes located at the ground surface around the reservoir and the current source and sink placed in and out of the reservoir, respectively. This method allows localizing the secondary current distribution associated with leakage using the distribution of potential recorded on a set of electrodes during the mise-à-la-masse experiment. An initial model based on the distribution of root mean square values between the observation and the simulation data is first given to the inversion algorithm. The Tikhonov regularization, which includes a weighting matrix and a minimum support function, is used to strengthen the detection resolution of the leak. 29 sandbox experiments show that the proposed method and inversion algorithm can localize a single leak. For a leak with a crack shape, the inversion algorithm detects the location of the leak with a small bias. When the leak lasts, a conductive zone may occur below the leak due to the increase of water content or ionic strength of the pore water. The occurrence of such a conductive body could affect the localization of the leak because the conductivity distribution may not be well-resolved. The effect is analyzed using synthetic experiments. The results show that the bias between the real leak and inversion results increases with the position and size of the undetected conductive zone. Two small-scale field tests were conducted to test the performance of the mise-à-la-masse method. The two leaks are properly identified. This study provides an efficient approach to detect the bottom leakage of reservoirs.
No abstract is provided for this article.
No abstract is provided for this article.
This paper presents the Cemagref work in the field of diagnosis aid applied to dam ageing. The context is a portfolio of 250 dams under the supervisory of the environment ministry and involving public safety. These dams are characterised by a relative heterogeneity in their conception, age and management modes. First, the paper presents this dam portfolio. Our approach proposes to capitalise on feedback and expert knowledge, in order to improve dam diagnosis. Our work has started with computer researches, in order to model expert’s process of reasoning by dam ageing scenarios. We have produced a decision making aid system for dam ageing diagnosis. This system is able to manage historic and ageing scenario databases. Then, we have developed with LERMES/CUST a dam degradation model in order to build up the scenarios. Our methodology is based on functional modelling and FMEA method. Our main goal is to build up a dam ageing scenario database and to manage this database with the decision making tools.
No abstract is provided for this article.
No abstract is provided for this article.
. The experience feedback on a crisis that hit a city is frequently used as a "recollection" tool. To capitalize information about an experience feedback from the cities that have been affected by a natural hazard, the authors propose in this study a functional model to model scenarios of city crises. In this model, the city, considered as a complex system, was modelled using a functional analysis method. Based on such modelling, two risk analysis methods (Failure Mode and Effect Analysis and Event Tree Method) were deployed and adjusted. Lastly, a qualitative reasoning model was used for the scenario modelling of the urban crisis. By functional modelling performed on components of the cities, the objective of this model is to replicate the behaviour of a city affected by a crisis, highlighting the sequences of failure and non-failure modes that have operated during the crisis. This model constitutes a means of understanding the functional behaviour in a crisis of cities and capitalization of the experience feedback of the cities affected by crisis. Such functional modelling was deployed in a case study.
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This paper reviews Cemagref (Centre national du machinisme agricole, du génie rural, des eaux et des forêts) research on assessment of hydraulic works, especially on their performance and safety. A generic functional model has been developed, using reliability methods, to represent the various mecanisms acting on different hydraulic works (gravity and embankment dams, fluvial dikes, etc.). Collecting and analyzing data on the failure of these works allowed us to define structural indicators and the rules for their assessment. Performance indicators for hydraulic works were created through multicriteria aggregation methods; various results were thus obtained. A database of knowledge relating to mechanisms and histories of dam ageing has been produced and constitutes a useful aid for consulting civil engineers. Methods and tools have been developed to assess the performance of fluvial dikes and to assist managers in planning maintenance operations. Similar research is under way on embankment dams and will provide a diagnosis tool for hydraulic works in operation.
RESUME – L'article presente a travers le recent guide de recommandations Retenues d’altitude la synthese d'un retour d’experience sur le comportement et la pathologie des dispositifs d’etancheite par geomembrane en altitude. Il donne les recommandations fortes du guide relatives a ces dispositifs, en particulier sur la structure support, le drainage inherent au DEG et la structure de recouvrement. Un descriptif general du guide termine l'article. Mots-cles : Retenues, altitude, etancheite, geomembrane, recommandations
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Determining discontinuities is a key step in studying rock mass stability, as they represent potentially weak planes. The determination and description of discontinuity openings currently rely on qualitative analysis based on visual inspections of drill cores or drilling logs by engineers. The purpose of this research work is to improve the characterization of discontinuities to ensure easier classification and aid classical manual and visual processing. Quantity-based approaches are suggested using acoustic imaging log data. This method will facilitate sorting the discontinuities in a rock mass according to their openings, by quantitative analysis of drilling log data. Here, a method is proposed to determine discontinuity openings by analyzing acoustic wave amplitudes. The method is based on determining two statistical parameters for each discontinuity: the resulting discontinuity amplitude, which provides the average amplitude value as measured on the discontinuity, and the discontinuity amplitude standard deviation, which determines the extent of scattering of the amplitude values on the discontinuity. The method was applied to a metamorphic rock mass of a Canadian dam foundation at each stage of the study.
