Contribution à la modélisation du comportement mécanique d'un matériau hétérophasé rematérialisé issu d'un mâchefer d'incinération d'ordures ménagères (valorisation en Génie Civil)

Les mâchefers sont les résidus solides issus de la combustion des ordures ménagères dans des fours d usine d incinération. L utilisation des mâchefers dans le domaine du Génie Civil est une voie de valorisation très intéressante car les quantités d ordures ménagères sont de plus en plus importantes alors que les matériaux utilisés dans les travaux publics se raréfient. Les mâchefers ont été utilisés depuis des dizaines d années dans le domaine du Génie Civil. Cependant, les caractéristiques mécaniques du matériau mâchefer ne sont pas très bien connues. Ce travail de thèse contribue à l amélioration des connaissances des caractéristiques mécaniques des mâchefers.Après une caractérisation géotechniques (paramètres de nature, paramètres mécaniques, paramètres d état), chimiques et environnementales, le potentiel d utilisation de ces mâchefers est évalué selon la Circulaire du 9 mai 1994 et selon le Guide technique SETRA-LCPC 2000 Réalisation des remblais et des couches de forme .Dans la partie expérimentale, des essais oedométriques et triaxiaux sont effectués. En ce qui concerne des essais oedométriques, l effet de l énergie de compactage et de l immersion des éprouvettes ainsi que l effet de la vitesse de chargement de l essai sont évalués. L effet de la vitesse de chargement est également étudié par des séries d essais triaxiaux. Grâce aux essais triaxiaux, les paramètres mécaniques comme le module d Young, le coefficient de Poisson, l angle caractéristique, l angle de dilatance, la cohésion et l angle de frottement ont été ainsi déterminés. Ces paramètres mécaniques propres au mâchefer étudié pourront être intégrés dans un schéma de dimensionnement spécifique aux structures de chaussées à base de mâchefers. Ces principaux paramètres permettent d évaluer l influence de la pression de confinement effective. Les évolutions du module de déformation selon la déformation axiale et de la variation du déviateur de pression selon la pression moyenne sont également étudiées. Un ensemble de points caractérisant l état limite a été déterminé à partir des essais triaxiaux. Il caractérise la forme de la surface de charge de ce type de mâchefer.Enfin, les essais triaxiaux ont été simulés. Cette partie du travail contribue à la modélisation du comportement mécanique des mâchefers. Le modèle de Mohr-Coulomb et de Nova sont choisis pour caractériser l évolution de matériau mâchefer sous l effet d actions mécaniques extérieures. Ce sont des exemples types de modèles de comportement des sols complètement identifiables uniquement sur des essais triaxiaux classiques. La simulation des essais triaxiaux est réalisée à l aide du progiciel CESAR-LCPC. Les résultats de modélisations obtenues sont très prometteurs.Bottom ash is the solid residua coming from domestic waste combustion in the furnace of incineration factory. The utilization of bottom ash in the field of Civil Engineering is necessary because the municipal wastes are increasing causes many environmental problems while the materials of Civil Engineering dwindle. The bottom ash was used for a decade in the field of civil engineering; however the mechanical characteristics of material bottom ash are not very well known. This work of thesis contributes to improving knowledge of the mechanical characteristics of bottom ash. After the determination of the geotechnical characteristics (parameters of nature, mechanical parameters, parameters of state), chemical and environmental characteristics, the potential of use of these bottom ash is evaluated according to the Circulaire de 9 Mai, 1994 and according to the technical guide SETRA-LCPC 2000 Réalisation des remblais et des couches de forme .In the experimental part, the oedometric and triaxial tests are carried out. For oedometric tests, the effect of compaction energy and immersion of specimens as well as the effect of the loading rate of the test were evaluated. The effect of loading rate is also evaluated by some sets of triaxial tests. From the triaxial tests, the mechanical parameters such as the Young s modulus, the Poisson s ratio, the characteristic angle, the dilatancy angle, the cohesion and the friction angle were determined. These mechanical properties are specific to the material and can be integrated in a diagram of dimensioning specific to the structures of roadways based on bottom ash. The studied principal parameters allow us to evaluate the influence of the effective confining pressure. The evolution of the deformation modulus versus to the axial deformation and finally, the variation of the deviator stress versus to the mean effective pressure were also analyzed. A set of points of the yielding state was determined from triaxial tests and it specifies significantly the shape of yielding surface of our bottom ash.Finally, the triaxial tests were simulated numerically. This part is a contribution to the modelling of the mechanical behaviour of bottom ash. The model of Mohr-Coulomb and Nova were chosen to characterize the evolution of the material bottom ash under the influence of external mechanical actions. These are typical examples of model soil completely identifiable only through traditional triaxial tests. The simulation of triaxial tests is carried out using the CESAR-LCPC software. The results are found to be promising.ARRAS-Bib.electronique (620419901) / SudocSudocFranceF

Validation of the gpu based blaze-dem framework for hopper discharge

Understanding the dynamical behavior of particulate materials is extremely important to many industrial processes, with typical applications that range from hopper flows in agriculture to tumbling mills in the mining industry. The discrete element method (DEM) has become the defacto standard to simulate particulate materials. The DEM is a compu- tationally intensive numerical approach that is limited to a moderate amount (thousands) of particles when considering fully coupled densely packed systems modeled by realistic par- ticle shape and history dependent constitutive relationships. A large number (millions) of particles can be simulated when the coupling between particles is relaxed to still accurately simulated lesser dense systems. Massively large scale simulations (tens of millions) are possi- ble when particle shapes are simplified, however this may lead to oversimplification when an accurate representation of the particle shape is essential to capture the macroscopic transport of particulates. Polyhedra represent the geometry of most convex particulate materials well and when combined with appropriate contact models predicts realistic mechanical behavior to that of the actual system. Detecting collisions between polyhedra is computationally ex- pensive often limiting simulations to only hundreds of thousands of particles. However, the computational architecture e.g. CPU and GPU plays a significant role on the performance that can be realized. The parallel nature of the GPU allows for a large number of simple independent processes to be executed in parallel. This results in a significant speed up over conventional implementations utilizing the Central Processing Unit (CPU) architecture, when algorithms are well aligned and optimized for the threading model of the GPU. We recently introduced the BLAZE-DEM framework for the GPU architecture that can model millions of pherical and polyhedral particles in a realistic time frame using a single GPU. In this paper we validate BLAZE-DEM for hopper discharge simulations. We firstly compare the flow-rates and patterns of polyhedra and spheres obtained with experiment to that of DEM. We then compare flow-rates between spheres and polyhedra to gauge the effect of particle shape. Finally we perform a large scale DEM simulation using 16 million articles to illustrate the capability of BLAZE-DEM to predict bulk flow in realistic hoppers

Self-compacting Backfills using Fly Ash and Dredged Marine Sediments for Public Work Applications

Sediment accumulation at the bottom of ports disrupts maritime activities and disturbs the physicochemical balance of water bodies. In France, the maintenance of the 6500-kilometer long coastline would require the extraction of about 50 million m3 of marine sediments every year. For several years, these sediments were considered waste. However, they are increasingly being acknowledged as a resource in need of management. Several research studies were conducted to find valorization ways that satisfy technical and regulatory requirements. These sediments present interesting heterogeneous physicochemical, mineralogical, and geotechnical characteristics. However, they may contain contamination, which could limit their uses. This paper deals with the possibility of producing self-compacting backfills using dredged marine sediments, fly-ash, and hydraulic binders for public work applications. The impact of dredged sediments on the composition of self-compacting backfills was studied. Moreover, the impact of fly ash and binder type and percentage on the backfill behavior and mechanical properties was discussed

New advances in large scale industrial DEM modeling towards energy efficient processes

Granular material processing is crucial to a number of industries such as pharmaceuticals, construction, mining, geology and primary utilities. The handling and processing of granular materials represents roughly 10% of the annual energy consumption [1]. A recent study indicated that in the US alone, current energy requirements across Coal, Metal and Mineral Mining amounts to 1246 TBtu/yr, whereas the practical minimum energy consumption is estimated to be 579 TBtu/yr, while the theoretical limited is estimated around 184 TBtu/yr [2]. It is evident that design modification allowing for process optimization can play a significant role in realizing a more energy efficient industry sector that can have significant implications on the annual global energy demands. The status quo in industry when facing the complex physics governing granular materials, is that current industry developed strategies to handle granular materials remain overly conservative and often energy-wasteful to prevent or reduce industrial-related bulk material handling problems like segregation, arching formation, insufficient handleability. Granular scale approaches have also been developed to both understand the fundamental physics governing granular flow and to study industrial applications, especially to improve the understanding and estimation of energy dissipation and energy efficiency of granular flow processes. The Discrete Element Method (DEM) proposed by Cundall and Strack [3] is starting to mature and evolve into a systematic approach to estimate and predict the response of granular systems. However, DEM is computationally intensive and is limited by the number of particles that can be considered realistically are limited to hundreds of thousands or low millions. However, before DEM can be practically considered for industrial applications the number of particles need be increased to tens of millions particles for a sufficient amount of processing time. This study discusses new advances and perspectives made possible by the Graphical Processor Unit (GPU) when simulating discrete element models, specifically for granular industrial applications. Attention is specifically focussed on the newly developed BlazeDEM3D-GPU framework for an industrial flow investigation [4]. Note that BlazeDEM3D-GPU is an open-source DEM code developed by Govender et al. [5] that has been validated for industrial ball mill simulations and hopper discharge applications using ten of millions of particles using a single NVIDIA GPU card on a desktop computer [4, 6]. The industrial granular flow investigation considered in this study is of the storage silos located at the industrial concrete central in France. The typical silo diameter is 8m with a height of around 17m. Three dimensional DEM studies were been performed to investigate the influence of particle sizes and inter-particle cohesion on the bulk flow rate and induced shear stresses for various hopper designs located at concrete central. As required for this industrially relevant application, up to 32 million particles were required to be simulated within a reasonable computing time. These simulations were performed within these requirements but only made possible by the utilization of GPUs. These results show that the GPU computing allows for realistically relevant number of simulated particles for the 3D DEM applications within a reasonable time frame. This makes large-scale analysis practically relevant but more importantly allows for a number of analyses to be conducted to steer granular processing solutions towards an increased efficiency in energy utilization

Marine Dredging Sediments Valorization in Self-Compacting Concretes

Rock and eroded soil are transported by wind, tide, and human action (development works), and deposited as sediment in ports, estuaries, and rivers. The sediment accumulation at the bottom of ports disrupts maritime activities and disturbs the physicochemical balance of water bodies. As a result, dredging is necessary to reduce sediment deposits and restore the natural environment for proper port functioning. At the national level, the maintenance of the 6,500-kilometer French coastline would require the extraction of about fifty million cubic meters of marine sediment every year. These dredged sediments have been used in civil engineering applications for about ten years, in order to reduce their economic and environmental impact. The proposed study addresses the potential use of sediments to produce accropode blocks for maritime public works applications. It consists in developing concrete mixtures using dredged marine sediment treated to protect against erosion. A study of material characterization, optimization of the composition of the concrete formulation, as well as a determination of the mechanical, physical and durability properties of the concrete were necessary to validate the technical feasibility of this new solution. Around 700 small accropode blocks were then prepared to better analyze the structure stability against swell effects. The obtained results show that the sediments could not produce Self Compacting Concrete (SCC). However, sediment treatment with 6% by weight of cement has enabled the production of SCC. It is worth noting that the use of superplasticizer was essential to ensure concrete workability. Increasing the cement percentage has also improved the composite workability. Finally, a concrete compressive strength greater than 40 MPa has been achieved when using 300 kg/m3 of treated sediments

3D laser scanning technique coupled with DEM GPU simulations for railway ballasts

Spheres with complex contact models or clumped sphere models are classically used to model ballast for railway applications with the Discrete Element Method (DEM). These simplifications omits the angularity of the actual ballast by assuming the ballast is either round or has rounded edges. This is done by necessity to allow for practically com- putable simulations that may consist of a few hundred particles. This study demonstrates that an experimentally validated DEM simulation environment, BlazeDEM-3DGPU, that computes on the graphical processing unit (GPU) is able to simulate railway ballast with a more realistic shapes that includes angularity for railway applications. In particular, a procedure is developed that extracts polyhedral shaped ballast geometries digitized from 3D-laser scanning for use in DEM simulations. The results show that much larger number of particles can be successfully modelled allowing for new possibilities offered by the GPUs to investigate model railway problems using DEM. Specifically, in this study a typical experimental ballast box that contains up to 60 000 polyhedral particles have been simulated with the BlazeDEM-3DGPU computing environment within reasonable computing times

The GeDSeT project: constitution of a decision support tool (DST) for the management and material recovery of waterways sediments in Belgium and Northern France

International audienceThe European InterReg IV GeDSeT project (2008-2011) is a contribution to a sustainable management of waterways sediments, in order to develop good practice in a perspective of water resource protection and of the development of regional fluvial transport. Waterways sediments are a major environmental issue in the Walloon region of Belgium - Northern France trans-boundary region for several reasons, all of them resulting from the dense habitat, industrial pattern and waterways network, and of a long industrial history. Sediments affect water resources quality, through pollution, and availability, through flooding. Sediment dredging allows the development of environmentally-friendly regional fluvial transport, but also generates important waste deposits. Therefore material recovery for reuse in buildings or infrastructure is a key issue, as it allows a reduction of waste and limits the need for natural resources for the same use. In order to address waterways sediments management in a global way, the GeDSeT project intends to capitalise know-how regarding the criteria to take into account for a sustainable management, and to include them in a decision support methodology applicable to the transboundary context. Such decision support aims at developing good practice in a perspective of water resource management and development of regional fluvial transport. Relevant criteria include: - criteria evaluating the physical and chemical characteristics of the sediments to be dredged, and their level of contamination, - costs of dredging operations and benefits with respect to improved waterways, - potential material value and costs of sediment treatment for material recovery versus costs of sediment deposit management. The decision support methodology will rely in part on previous BRGM and European experience in the development of an environmentally extended, physical, quasi-dynamic input-output model for waste management. Experience from other specific DSTs on sediments will be valorised with the project partners. Potential recovery of secondary resources from dredged sediment will be addressed through a review and economic evaluation of available technologies, technical and economical constraints, side effects on the uses of recovered products, and a global balance of the environmental costs and benefits. Social and employment impacts, as well as land use issues in this densely populated area will be fully acknowledged as primary decision-support criteria. The expected benefit of the project comprises also the transboundary comparison of specific situations and methods, issued from a different history.Le projet InterReg IV GeDSeT (2008-2011) est une contribution à une gestion globale durable des sédiments des voies d’eau, au développement du transport régional fluvial et de bonnes pratiques pour la protection des ressources en eau et de l’espace urbain.Les sédiments des voies d’eau sont un enjeu majeur en Europe, et particulièrement dans la région transfrontalière Belgique Wallonie – Nord de la France pour plusieurs raisons, toutes liées à la densité de l’habitat, du tissu industriel passé et présent, et du réseau de voies d’eau. Non seulement les sédiments affectent la navigabilité, mais aussi la qualité des ressources en eau, par la pollution, et la gestion des inondations. Le curage régulier des sédiments permet le développement d’un transport régional fluvial éco-favorable, mais génère d’importants volumes de déchets potentiels. La réutilisation des sédiments pour la construction ou les infrastructures est donc un enjeu clé, en combinant réduction des déchets et des besoins en ressources naturelles pour le même usage.Afin de prendre en compte la problématique des sédiments fluviaux dans sa globalité, le projet GeDSeT va capitaliser l’état de l’art sur les critères pertinents pour une gestion durable, et les incorporer dans une méthodologie d’aide à la décision applicable au contexte transfrontalier. Cette méthodologie vise à développer des bonnes pratiques en harmonie avec la gestion des ressources en eau, et le développement du transport fluvial régional

Boundary condition enforcement for renormalised weakly compressible meshless Lagrangian methods

This paper introduces a boundary condition scheme for weakly compressible (WC) renormalised first-order accurate meshless Lagrangian methods (MLM) by considering both solid and free surface conditions. A hybrid meshless Lagrangian method-finite difference (MLM-FD) scheme on prescribed boundary nodes is proposed to enforce Neumann boundary conditions. This is used to enforce symmetry boundary conditions and the implied Neumann pressure boundary conditions on solid boundaries in a manner consistent with the Navier-Stokes equation leading to the accurate recovery of surface pressures. The free surface boundary conditions allow all differential operators to be approximated by the same renormalised scheme while also efficiently determining free surface particles. The boundary conditions schemes are implemented for two renormalised MLMs. A WC smoothed particle hydrodynamics (SPH) solver is compared to a WC generalised finite difference (GFD) solver. Applications in both 2D and 3D are explored. A substantial performance benefit was found when comparing the WCGFD solver to the WCSPH solver with the WCGFD solver realising a maximum speedup in the range of three times over WCSPH in both 2D and 3D configurations. The solvers were implemented in C++ and used the NVIDIA CUDA 10.1 toolkit for the parallelisation of the solvers.http://www.elsevier.com/locate/enganaboundhj2022Mechanical and Aeronautical Engineerin

Ecoulement d'un materiau granulaire a travers un orifice. Effet de paroi

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 79838 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc