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Mine de sel d’Urcuit (France) : une approche globale de la procédure d’arrêt définitif des travaux miniers
No full textInternational audienceLa mine de sel d’Urcuit est située au sud-ouest de la France, près de Bayonne, entre la plaine piémontaise des Pyrénées et la vallée de l’Adour. L’exploitation minière, qui a duré plus d’un siècle, a consisté en l’exploitation, par dissolution, de plus de 5 millions de tonnes de sel du Trias présent localement entre 20 et plus de 200 m de profondeur. Plusieurs techniques de dissolution ont été mises en oeuvre, créant plus de 80 cavités isolées ou connectées, dont un grand nombre sont encore présentes dans le sous-sol. Par le passé, des affaissements de terrain ou des effondrements en surface ont été localement observés et associés à des configurations géologiques, hydrogéologiques et minières particulières. En application des dispositions du Code Minier, l’exploitant a engagé une procédure d’arrêt des travaux miniers et a confié à l’Ineris, en 2013, la réalisation de l’ensemble des pièces techniques et administratives du dossier de Déclaration d’Arrêt Définitif de Travaux miniers (DADT). Grâce à deux années d’investigations sur le terrain, l’Ineris a pu appréhender précisément les contextes géologiques, géotechniques et hydrogéologiques du site afin d’évaluer, sur le long terme, la stabilité des cavités connues. Les investigations menées sur les eaux de surface et souterraines montrent que les processus de dissolution sont toujours actifs sur le site d’Urcuit mais leur extension et leur intensité sont fortement réduites du fait de l’arrêt de l’exploitation et des aménagements réalisés. L’analyse en retour d’expérience des mesures des mouvements de terrain et la connaissance de l’état actuel des cavités (volume, forme, profondeur) ont été utilisées pour évaluer les potentialités de mouvements de terrain résiduels. L’étude géomécanique de la stabilité des cavités par modélisation numérique, prenant en compte la spécificité rhéologique du sel, a également complété cette évaluation. Afin de limiter l’impact des anciennes exploitations et de s’assurer de la stabilité des cavités et de l’absence de rejets trop importants de saumure dans l’environnement, des mesures compensatoires, adaptées aux enjeux, ont été proposées. Après le premier donné acte de l’Administration à la mi-2017, les travaux de fermeture et de surveillance de la mine ont commencé et certains dureront plusieurs années
People evacuation in tunnel fires : a cross evaluation of two methodologies
No full textInternational audienceIn France, safety assessment of tunnels is mainly based on a risk analysis called the specific hazard investigation. One of the key issues of these studies consists in modeling people evacuation. The commonly used method for computing the people evacuation consists in evaluating their displacement velocity based on smoke opacity. However, it is obvious that other fire consequences parameters, thermal effects and toxicity, will affect people displacement. To evaluate whether considering those effects is relevant and could modify conclusions of specific hazard investigations in tunnels or not, two approaches were used in a comparative manner. The first approach is based on currently used method and considers only the smoke opacity. The second innovative approach introduces thermal and toxic consequences on the displacement velocity. It enables considering the toxic dose impact on human being during the evacuation process and the thermal effect together with the visibility. This new approach also introduces a new method for the evaluation of lethality and user evacuation which are managed with thresholds in the current method. This difference was also considered in the comparison. Those two approaches were applied on many fire scenarios to compare the conclusions in terms of people trapped or killed by the fire. For each of those scenarios, consequences were evaluated based on a CFD model, for different tunnel geometries, design fires and ventilation strategies. The two most relevant of those scenarios are presented in the present paper. This comparison shows only minor differences for the specific case of tunnel fire safety. One way to consider the effect of the new methodology should consist in keeping the existing method but modifying the corresponding thresholds for the different quantities relative to fire consequences
Mining subsidence in a partially flooded abandoned mine : aseismic ground movement and consequences for post-mining risk management
No full textInternational audienceIn the Lorraine area of eastern France, decades of iron ore mining from 1850 to 1997 have left vast underground cavities beneath or near urban areas. Several major collapses occurred in the southern part of this iron ore basin in the 1990s, after the mine closure and the flooding of underground mine workings. Following these large scale collapses, the French government initiated a strategy of post mining risk management to prevent and control risks associated with these ground failures. The high risk zones are secured either by reducing the vulnerability while the moderate risk zones are monitored for public safety purposes by using in situ monitoring. This monitoring relies mainly on real time microseismic systems, to detect precursors to a rapid large scale collapse. Data recorded are processing automatically, and may generated alarm in case of abnormal evolution, in terms of number of event as well as in energy. A cell of expertise can be mobilized to analyse the situation and inform the local authorities of the evolutions of the situation. Evacuation can be triggered in case of danger for public safety. After the progressive closing and then flooding of the northern iron basin ending in 2008, subsidence was observed in a town of the Lorrain basin in autumn of 2009. However, this local subsidence, with a low velocity of few centimeters per month, was not clearly detected by the borehole microseismic monitoring station located nearby. Only some microseismic events were recorded, which could not be unambiguously related to the beginning of the subsidence event. To better understand this lack of microseismic precursor a geophysical investigation was launched. A calibration blast experiment was carried out from a remaining old underground access in order to characterise the wave propagation properties in this context. The results of this study show strong anelastic attenuation of the seismic waves though the monitored overburden most likely related to the extensive fault system intersecting the study site. Moreover, robbed pillar extraction and flooding of the site have induced a reduction of the mechanical properties of the overburden. These observations, added to a slow kinetics subsidence mechanism (~ cm/months) with little seismic energy release, may explain the lack of detected microseismicity during the subsidence event. In addition, low frequency microseismic events associated with the very slow subsiding movements might have not been detected by the used high frequency recording instruments, designed initially for rapid collapses (~ cm/hours)
Modified bauxite residue as filter Material to upgrade phosphorus removal in constructed wetlands : batch and column scale experiments
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Attempts of recovery of antimony from co-incinerated sorted brominated WEEE plastics by simple mineralurgical operations
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Stress measurement for evaluating nickel ore liquefaction during sea carriage
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Simulation of medicanes over the Mediterranean Sea in a regional climate model ensemble: impact of ocean–atmosphere coupling and increased resolution
No full textInternational audienceMedicanes are cyclones over the Mediterranean Sea having a tropical-like structure but a rather small size, that can produce significant damage due to the combination of intense winds and heavy precipitation. Future climate projections, performed generally with individual atmospheric climate models, indicate that the intensity of the medicanes could increase under climate change conditions. The availability of large ensembles of high resolution and ocean–atmosphere coupled regional climate model (RCM) simulations, performed in MedCORDEX and EURO-CORDEX projects, represents an opportunity to improve the assessment of the impact of climate change on medicanes. As a first step towards such an improved assessment, we analyze the ability of the RCMs used in these projects to reproduce the observed characteristics of medicanes, and the impact of increased resolution and air-sea coupling on their simulation. In these storms, air-sea interaction plays a fundamental role in their formation and intensification, a different mechanism from that of extra-tropical cyclones, where the baroclinic instability mechanism prevails. An observational database, based on satellite images combined with high resolution simulations (Miglietta et al. in Geophys Res Lett 40:2400–2405, 2013), is used as a reference for evaluating the simulations. In general, the simulated medicanes do not coincide on a case-by-case basis with the observed medicanes. However, observed medicanes with a high intensity and relatively long duration of tropical characteristics are better replicated in simulations. The observed spatial distribution of medicanes is generally well simulated, while the monthly distribution reveals the difficulty of simulating the medicanes that first appear in September after the summer minimum in occurrence. Increasing the horizontal resolution has a systematic and generally positive impact on the frequency of simulated medicanes, while the general underestimation of their intensity is not corrected in most cases. The capacity of a few models to better simulate the medicane intensity suggests that the model formulation is more important than reducing the grid spacing alone. A negative intensity feedback is frequently the result of air-sea interaction for tropical cyclones in other basins. The introduction of air-sea coupling in the present simulations has an overall limited impact on medicane frequency and intensity, but it produces an interesting seasonal shift of the simulated medicanes from autumn to winter. This fact, together with the analysis of two contrasting particular cases, indicates that the negative feedback could be limited or even absent in certain situations. We suggest that the effects of air-sea interaction on medicanes may depend on the oceanic mixed layer depth, thus increasing the applicability of ocean–atmosphere coupled RCMs for climate change analysis of this kind of cyclones
Resistance to explosion assessment of an electric transformer building
No full textInternational audienceThe ability of technical buildings to resist internal explosions produced by short circuits occurring in electrical transformers is an issue for the public authorities. Even if the probability of such an event is very low, the consequences can be significant and can easily put the surrounding public in danger due the blast, the projection of fragments and to the subsequent very toxic fire. The aim of this article is to investigate the consequences the blast on the structure of the technical building in which the transformer is located. The first part of this study deals with the estimation of the pressure load on the walls of the transformer’s building. A complete modelling of the phenomenology is proposed starting from the electrical energy delivered into the arc, its transformation into gases, the efforts applied through the liquid onto the casing of the container, the expansion of the gases inside the building, the blast wave produced and its interaction on the inner walls of the building. In particular, the characteristics (amplitude and duration) of the shock waves are evaluated using the modelling tool ‘DIFREX’, developed by INERIS. This tool considers the evolution of the shock waves intensity, during their propagation and their reflection on obstacles (like walls). The overpressure signals and their time evolution are calculated according to an optimized spatial discretization in order to get the worst case for the structure. The second part describes the modelling of the building structure using SAP2000 software in order to evaluate its dynamic behaviour and estimate the internal forces induced by the explosion. The structural behaviour depends mainly on the characteristic duration of the overpressure and the overall stiffness of the building. The calculation is performed according a dynamic transient analysis. The results in terms of displacement and the effect on the reinforcement are given