Etude des méthodes éprouvées et innovantes pour la surveillance des digues

National audienceNowadays flood protection dikes surveillance is mostly ensured by visual inspection. There is only few instrumental monitoring whereas it could be used as a relevant approach, complementary to visual inspection. In particular instrumental monitoring can offer continuous and/or wide range surveillance, which is especially useful when dealing with dikes. Instrumental monitoring methods can also help optimizing visual surveillance during flood, when human resources can be scarcer than usual. An overview of the tried and tested surveillance techniques as well as the innovative ones has been made. The objective was to summarize the pros and cons of each technique toward the main dikes failure mechanisms. The techniques have been chosen regarding their range, efficiency and capacity of producing a relevant and precise diagnosis. The development level has also been evaluated through the feedbacks that could be identified. A specific focus is also given on the time and resources needed for data processing and interpretation.Aujourd'hui la surveillance des digues de protection contre les inondations est essentiellement assurée par examen visuel. La surveillance instrumentale est peu développée bien qu'elle puisse être considérée comme une approche complémentaire pertinente qui permettrait de pallier les limites pratiques de l'examen visuel : difficultés d'établir une surveillance continue dans le temps et sur des linéaires importants avec des ressources humaines limitées, notamment en période de crue. Afin d'évaluer les apports potentiels de méthodes instrumentale à la surveillance des digues, un état de l'art a été réalisé. Il a eu pour objectif de présenter de manière synthétique les avantages et limites de chaque méthode au regard des mécanismes de rupture susceptibles d'être détectés. Les méthodes ont été sélectionnées en fonction de critères opérationnels : - en premier lieu leur capacité à établir un diagnostic précis vis-à-vis d'un risque donné ; - leur grand rendement, caractéristique essentielle pour surveiller un objet étendu ; - les moyens et le temps nécessaires au traitement et à l'interprétation des données. Cet aspect deviendra notamment critique en période de crue. Ont été considérées à la fois les techniques éprouvées et les méthodes innovantes, parfois encore au stade de R&D. Dans ce cas la maturité de la technologie a été évaluée au regard des retours d'expérience identifiés. Enfin la notion de coût est abordée. Chaque technique retenue est décrite, la conclusion faisant la synthèse des constatations faites. Cet état de l'art pourra être consulté de manière plus complète au travers du rapport publique remis au MEDDE et disponible à la date de parution de cette communication

Surveillance acoustique des cavités à risque de fontis et d'effondrements localisés

National audienceIt is very difficult to monitor sinkholes and local collapses from underground using the classical geotechnical instrumentation since the location of such pre-existing phenomena cannot be easily approached or forecast in time in wide and complex underground cavities. INERIS developed and tested an acoustic method to detect, localize and characterize rock falls with the help of a few sensors.Les cavités souterraines de faible profondeur, naturelles ou anthropiques, peuvent être à l'origine de risques de mouvements de terrains par fontis ou par effondrement localisé. Ce phénomène touche l'ensemble du territoire national. Dans l'attente d'un traitement, une surveillance peut permettre de gérer le risque. Jusqu'à présent, cette surveillance était essentiellement réalisée par inspection visuelle et par instrumentation géotechnique conventionnelle. Cette démarche présentant plusieurs limites dans le suivi des phénomènes dans la continuité et d'exposition des équipes intervenantes, il était important d'examiner de nouvelles solutions instrumentales

Evolution monitoring of a solution-mining cavern in salt : identifying and analysing early-warning signals prior to collapse

International audienceRisk management of underground cavities requires a good working knowledge of accidental phenomena like subsidence or large-scale collapse. This was the context when the opportunity was taken to instrument a large size in use saline cavern, so as to test various auscultation techniques available under controlled conditions. A microseismic monitoring network coupled to a surface measurement system was installed to improve our knowledge of the mechanisms that initiate and govern the evolution of the cavern up to its collapse. After a stationary period combined with partial depressurization tests conducted in 2005 and 2007, the cavern appears to have entered into its final evolution phase, and this probably since early 2008. This results in continuous and highly sustained microseismic activity as well as the occurrence of a number of microseismic episodes localized around the cavern roof. The localization of the microseismic events, for some of these episodes, is closely correlated to the quasi-dynamic brine pressure variations and to the evolutions of the roof depth measured at observation boreholes. The microseismic activity turns out to be more precise when it comes to the evolution affecting the mine cavern than the movement measurements taken on the surface or sub-surface

Monitoring of ground failures in subsurface complex cavities

International audienceRisk prevention related to complex extended cavities raises often strong economic, social and/or technical issues for local authorities and decision-makers. Remote monitoring offers a median way of vulnerability mitigation. However relevant monitoring of those geohazards calls for innovative volumetric methods to meet reasonable cost/benefit ratios, as microseismic and aerial acoustic monitoring techniques. Aerial acoustic technique has been developed and tested by INERIS in several underground contexts. This paper presents feedback from both experimental and operational case studies, presents results and recommendation for proper field applicatio

Global monitoring strategy applied to ground failure hazards

International audienceRisk management of natural ground failures or those of anthropogenic origin by means of operational monitoring requires the setting-up of performing early-warning systems. The goal is to sufficiently anticipate the natural catastrophe, unpredictable in time, and thereby guarantee acceptance of the risks by effective reduction in the vulnerability, including the case of multiple risks and of domino effects. Beyond in-depth hazard assessment study, in terms of mechanisms and scenarios, the early-warning system should allow quasi real-time integration of the factors identified as worsening, precursory and triggering factors, to which are added specific monitoring of the dreaded hazard and that of the most vulnerable stakes. Such a global monitoring strategy and the resulting technological choices to be deployed, developed by the CENARIS, at INERIS, are explained and illustrated by means of concrete examples

Retours d'expérience sur un affaissement minier et sur l'effondrement d'une cavité. Suivi de mouvements de terrain par GPS différentiel

International audienc

Detection of underground instabilities in an old limestone quarry through acoustic monitoring

The presence of abandoned and unstable underground cavities can give rise to a potential risk of surface collapse, particularly alarming when the presence of buildings is attested on the surface. The INERIS (Institut National de l’Environnement Industriel et des Risques, France) has carried out many studies, in recent years, investigating the effectiveness of several methodologies to monitor the evolution of the damaging mechanisms. During 2012 the Brasserie quarry, an old limestone mine (Paris, France) was instrumented with microphones to detect the acoustic waves generated by the collapse of blocks from the roof and the walls of the cavity. A series of tests were carried out to determine the propagation characteristics. Preliminary data processing concerned the event classification and the analysis of the signal-to-noise ratio (SNR). In the present paper, after the description of the case study, the preliminary results and the description of the upcoming works and expectation will be outlined