Experimental Investigation of Saturation Effect on the Mechanical Behaviour of Château-Landon Chalk

International audienceAbandoned underground mines appear to be very sensitive to the variations in their environment. Due to seasonal environmental changes often related to climate and resulting in changes in the water table and hygrometry, the pillars are often subjected to cyclic variations of saturation. This could affect the short- and long-term stability of these abandoned structures. In this paper, a preliminary study on the behaviour of Château-Landon chalk has been carried out. Samples were extracted from pillars of the abandoned Royer chalk mine (Château-Landon, France). The mechanical behaviour of this chalk was then investigated by performing conventional hydrostatic, triaxial compression, and creep tests under drained conditions at different water saturation degrees and confining pressures. The obtained results show up fundamental aspects of this chalk behaviour. Its high sensitivity to water and confining pressure are described, and a water saturation-induced plastic deformation is analysed. The results presented in this paper provide some key mechanisms that can be used in the framework of back analysis and expertise in underground chalk mines, as well as the data required for the development of a specific constitutive model

Study of the behaviour of walls and doors of 20 ft ISO containers through real-scale explosion tests

International audienceISO containers are increasingly used to house processes involving a potential explosion risk such asBattery Energy Storage Systems or hydrogen-based systems. For both examples, explosions may bepowerful because of the potentially large obstruction in the container promoting flame accelerationand/or the high dynamics of the hydrogen flames.An important part of the modelling strategy for predicting residual pressure effects of an explosion inan ISO container is the knowledge of the mechanical behaviour of the structure initially confining theflammable cloud.In order to improve knowledge regarding the mechanical behaviour of the container and get adatabase suitable for validation purposes of the modelling tool, hydrogen explosions tests in 20-footISO containers were performed at INERIS testing facilities. The goal was to generate distinctivepressure signals and to collect comprehensive measurements related to the mechanical behaviour ofthe doors and walls.The paper details the experimental set-up, the metrology dedicated to mechanical measurements andthe main results. First conclusions of the experimental campaign are also supplied.Thus, the comparative analyses of dynamic explosion load tests (20%, 22%) highlight the significantdifferences in the intensity of the stress imposed on the structure of the container. The 20% testpresents less severe conditions with reduced deformations and recorded stresses compared to the 22%test. These results underline the importance of considering the variable nature of dynamic loads whenevaluating container resistance and offer valuable insights for improving the design of protectivebarriers (like explosion vent panels for example) in similar conditions

Aerosol source apportionment uncertainty linked to the choice of input chemical components

International audienceFor a Positive Matrix Factorization (PMF) aerosol source apportionment (SA) studies there is no standard procedure to select the most appropriate chemical components to be included in the input dataset for a given site typology, nor specific recommendations in this direction. However, these choices are crucial for the final SA outputs not only in terms of number of sources identified but also, and consequently, in the source contributions estimates. In fact, PMF tends to reproduce most of PM mass measured independently and introduced as a total variable in the input data, regardless of the percentage of PM mass which has been chemically characterized, so that the lack of some specific source tracers (e.g. levoglucosan) can potentially affect the results of the whole source apportionment study. The present study elaborates further on the same concept, evaluating quantitatively the impact of lacking specific sources’ tracers on the whole source apportionment, both in terms of identified sources and source contributions. This work aims to provide first recommendations on the most suitable and critical components to be included in PMF analyses in order to reduce PMF output uncertainty as much as possible, and better represent the most commons PM sources observed in many sites in Western countries. To this aim, we performed three sensitivity analyses on three different datasets across EU, including extended sets of organic tracers, in order to cover different types of urban conditions (Mediterranean, Continental, and Alpine), source types, and PM fractions. Our findings reveal that the vehicle exhaust source resulted to be less sensitive to the choice of analytes, although source contributions estimates can deviate significantly up to 44 %. On the other hand, for the detection of the non-exhaust one is clearly necessary to analyze specific inorganic elements. The choice of not analysing non-polar organics likely causes the loss of separation of exhaust and non-exhaust factors, thus obtaining a unique road traffic source, which provokes a significant bias of total contribution. Levoglucosan was, in most cases, crucial to identify biomass burning contributions in Milan and in Barcelona, in spite of the presence of PAHs in Barcelona, while for the case of Grenoble, even discarding levoglucosan, the presence of PAHs allowed identifying the BB factor. Modifying the rest of analytes provoke a systematic underestimation of biomass burning source contributions. SIA factors resulted to be generally overestimated with respect to the base case analysis, also in the case that ions were not included in the PMF analysis. Trace elements were crucial to identify shipping emissions (V and Ni) and industrial sources (Pb, Ni, Br, Zn, Mn, Cd and As). When changing the rest of input variables, the uncertainty was narrow for shipping but large for industrial processes. Major and trace elements were also crucial to identify the mineral/soil factor at all cities. Biogenic SOA and Anthropogenic SOA factors were sensitive to the presence of their molecular tracers, since the availability of OC alone is unable to separate a SOA factor. Arabitol and sorbitol were crucial to detecting fungal spores while odd number of higher alkanes (C27 to C31) for plant debris

Recommendations for reporting equivalent black carbon (eBC) mass concentrations based on long-term pan-European in-situ observations

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Hydro-mechanical analysis of particle migration in fractures with CFD-DEM

International audienceParticle migration driven by fluid flow is presented in many geological and geotechnical contexts, such as sand production in oil exploitation, internal erosion in dikes or dams, and proppant movement in petroleum engineering. In this study, fluid flow-induced particle migration in rock fractures has been investigated by coupling the computational fluid dynamics (CFD) and the discrete element method (DEM), focusing on the particle movements and the associated migration mechanisms. To fit the fracture roughness, tetrahedral grids were used to generate the fluid mesh in CFD analysis. The CFD-DEM model was first calibrated against experimental and analytical results, then a series of simulations was conducted to analyze the effects of fracture roughness (defined by the joint roughness coefficient, JRC), size ratio between fracture aperture and particle diameter, and hydraulic gradient on the migration of particle assemblies. Three modes of particle movement were obtained, i.e., the movement of particle assemblies as a whole, the separation of large particle assemblies into smaller ones, and the detachment of particles at assembly boundaries. Additionally, the velocity of a particle assembly passing through the fracture was negatively related to the aggregation of particles while positively related to the erosion rate of particle assemblies within the fracture. An equation to calculate the time of a particle assembly to pass through a fracture was proposed

Induced Seismicity Controlled by Injected Hydraulic Energy: The Case Study of the EGS Soultz‐Sous‐Forêts Site

International audienceHow induced seismicity in deep geothermal project (enhanced geothermal systems, EGS) is controlled by fluid injection is of central importance for monitoring the related seismic risk. Here we analyze the relationship between the radiated seismic energy and the hydraulic energy related to the fluid injection during several hydraulic stimulations and circulation tests at Soultz-sous-Forêts geothermal site. Based on a harmonized database, we show that the ratio between these energies is at first order constant during stimulations and of the same magnitude independently of the stimulation protocol and injection depth. Re-stimulations are characterized by a sharp evolution of this ratio during injection which ultimately converges to the characteristic value of the reservoir. This supports that the seismicity is caused by the relaxation of the pre-existing strain energy in the stimulated volume, rather than by the deformation generated from fluid injection. The ratio appears as an intrinsic large-scale property of the reservoir that can be assessed at the very beginning of the first stimulation. Based on this property, we suggest a way to predict the largest magnitude of the induced seismic events knowing the maximum targeted hydraulic energy of the injection

Development of a detailed gaseous oxidation scheme of naphthalene for secondary organic aerosol (SOA) formation and speciation

International audienceNaphthalene is the most abundant polycyclic aromatic hydrocarbon (PAH) in vehicle emissions and polluted urban areas. Its atmospheric oxidation products are oxygenated compounds that are potentially harmful for health and/or contribute to secondary organic aerosol (SOA) formation. Despite its impact on air quality, its complex structure and a lack of data mean that no detailed scheme of naphthalene gaseous oxidation for SOA formation and speciation has been established yet. This study presents the construction of the first near-explicit chemical scheme for naphthalene oxidation by OH, including kinetic and mechanistic data. The scheme redundantly represents all the classical steps of atmospheric organic chemistry (i.e., oxidation of stable species, peroxy radical formation and reaction, and alkoxy radical evolution), thus integrating fragmentation or functionalization pathways and the influence of NOx on secondary compound formation. Missing kinetic and mechanistic data were estimated using structure–activity relationships (SARs) or by analogy with existing experimental or theoretical data. The proposed chemical scheme involves 383 species (231 stable species, including 93 % of the major molar masses observed in previous experimental studies) and 484 reactions with products. A first simulation reproducing experimental oxidation in an oxidation flow reactor under high-NOx conditions shows a simulated SOA mass on the same order of magnitude as has been observed experimentally, with an error of −9 %

Probabilistic slope stability analysis: A novel distribution for soils exhibiting highly variable spatial properties

International audienceSlope stability calculation depends on the soil properties (cohesion and the friction angle) of the soil. Heterogeneous terrains are frequently observed in civil and mining projects where the properties are highly spatially variable. Based on a real data from case studies, this paper presents a probabilistic analysis of the slope stability of highly heterogeneous terrains with a very high coefficient of variation (COV) of the cohesion distribution. The existing deterministic and probabilistic approaches for calculating slope stability lack the capability to effectively consider the significant heterogeneity present in the terrain The objective of the paper is to develop a new bounded interval distribution having a COV that is as high (>150%) as the COV of the cohesion distribution The results obtained with this new distribution are compared to 4 other semi-infinite distributions. To consider the correlation between cohesion and the friction angle, a specific formulation was developed to generate friction angles varying between fixed minimum and maximum limits and having the desired correlation coefficient, mean, and standard deviation. The new cohesion and friction angle distributions were incorporated and tested in a probabilistic numerical model. The new distribution can presently be applied to geotechnical studies for terrains and heterogenous materials with properties exhibiting high spatial variability

Some questions related to CFD modeling of pressurized tank burst in road tunnels

International audienceThe current paper focuses on high-pressure reservoirs and the consequences of their potential burst,related to scenarios of thermal or mechanical aggressions, in tunnels.CFD (Computational Fluid Dynamics) modeling can be used to account for the effects of suchscenarios. An intrinsic advantage of such an approach consists in integrating the specific geometricaleffects (tunnel walls, presence of vehicles) on the pressure wave propagation.To meet such an objective, experimental data are required to offer an opportunity for validation. Datafrom the literature and new ones from INERIS are detailed in this paper, with their strengths andweaknesses to identify relevant test cases for CFD.Phenomenological tools are tested against experimental cases of bursting tank in a free field toevaluate their prediction capability for pressure. These tools could be used along with CFD in a globalmodeling framework.CFD is tested against fictitious free-field cases, investigating the effect of the thermodynamic modelon the results. The numerical method for propagating the pressure wave in realistic tunnels is alsostudied

Assessment of Run-Off Waters Resulting from Lithium-Ion Battery Fire-Fighting Operations

International audienceAs the use of Li-ion batteries is spreading, incidents in large energy storage systems (stationary storage containers, etc.) or in large-scale cell and battery storages (warehouses, recyclers, etc.), often leading to fire, are occurring on a regular basis. Water remains one of the most efficient fire extinguishing agents for tackling such battery incidents, and large quantities are usually necessary. Since batteries contain various potentially harmful components (metals and their oxides or salts, solvents, etc.) and thermal-runaway-induced battery incidents are accompanied by complex and potentially multistage fume emissions (containing both gas and particles), the potential impact of fire run-off waters on the environment should be considered and assessed carefully. The tests presented in this paper focus on analyzing the composition of run-off waters used to spray NMC Li-ion modules under thermal runaway. It highlights that waters used for firefighting are susceptible to containing many metals, including Ni, Mn, Co, Li and Al, mixed with other carbonaceous species (soot, tarballs) and sometimes undecomposed solvents used in the electrolyte. Extrapolation of pollutant concentrations compared with PNEC values showed that, for large-scale incidents, run-off water could be potentially hazardous to the environment