46 research outputs found

    Numerical modelling of the nonlinear mechanical behavior of multilayer geosynthetic system for piggyback landfill expansions

    Get PDF
    Numerical modelling techniques have been increasingly used to assess the integrity of engineering works, such as landfills, that involve interactions between multiple geosynthetics GSYs). In piggyback landfill expansions (PBLEs), where a new landfill is built over an older one, such interactions are particularly important because multiple GSYs, natural materials, and waste interact with each over. To obtain reliable numerical results, the real mechanical behavior of the GSYs and of the interfaces between GSYs must be considered. Designers, however, often use simplistic assumptions without further analyzing the implications of these assumptions on the results. Such simplifications mainly concern the nonlinear axial stiffness of GSYs, the strain softening at interfaces between GSYs, and the difference between the compressive and tensile behavior of GSYs. By, considering these key aspects, the present study aims to understand the extent to which the results of numerical calculations can be influenced both by the differing compressive and tensile behavior of GSYs and by the assumption of strain softening at interfaces between GSYs. For this purpose, several numerical models are implemented by using the finite-difference code FLAC 2D on a typical PBLE that involves four GSYs and six interfaces. The present work also applies comprehensive, state-of-the-art numerical modelling to study the interactions between multiple layers of GSYs. This study also investigates the nonlinear axial stiffness of GSYs through a series of uniaxial tensile tests. The numerical results show that, if the GSY axial compressive and tensile characteristics are the same, then tensile force is minimized, which induces significant compressive force in the GSYs. The results also indicate that neglecting strain softening at the interface between GSYs affects interface shear stresses, displacements of GSYs at the interface, and the GSY force distribution, potentially rendering the model unrealistic. Including strain softening, however, allows the assessment (location) of unstable areas along the interface where large displacements occur

    Numerical modeling of the nonlinear mechanical behavior of multilayer geosynthetic system for piggyback landfill expansions

    Get PDF
    This paper was accepted for publication in the journal Geotextiles and Geomembranes and the definitive published version is available at http://dx.doi.org/10.1016/j.geotexmem.2016.07.004.Numerical modelling techniques have been increasingly used to assess the integrity of engineering works, such as landfills, that involve interactions between multiple geosynthetics GSYs). In piggyback landfill expansions (PBLEs), where a new landfill is built over an older one, such interactions are particularly important because multiple GSYs, natural materials, and waste interact with each over. To obtain reliable numerical results, the real mechanical behavior of the GSYs and of the interfaces between GSYs must be considered. Designers, however, often use simplistic assumptions without further analyzing the implications of these assumptions on the results. Such simplifications mainly concern the nonlinear axial stiffness of GSYs, the strain softening at interfaces between GSYs, and the difference between the compressive and tensile behavior of GSYs. By, considering these key aspects, the present study aims to understand the extent to which the results of numerical calculations can be influenced both by the differing compressive and tensile behavior of GSYs and by the assumption of strain softening at interfaces between GSYs. For this purpose, several numerical models are implemented by using the finite-difference code FLAC 2D on a typical PBLE that involves four GSYs and six interfaces. The present work also applies comprehensive, state-of-the-art numerical modelling to study the interactions between multiple layers of GSYs. This study also investigates the nonlinear axial stiffness of GSYs through a series of uniaxial tensile tests. The numerical results show that, if the GSY axial compressive and tensile characteristics are the same, then tensile force is minimized, which induces significant compressive force in the GSYs. The results also indicate that neglecting strain softening at the interface between GSYs affects interface shear stresses, displacements of GSYs at the interface, and the GSY force distribution, potentially rendering the model unrealistic. Including strain softening, however, allows the assessment (location) of unstable areas along the interface where large displacements occur

    Vers une durabilité accrue des géomembranes bitumineuses

    No full text
    Depuis une trentaine d'années, les géomembranes sont largement employées dans les ouvrages hydrauliques, notamment pour assurer leur étanchéité. Dans un souci de préservation de l'environnement, il est donc essentiel de mieux connaître la durabilité de ces produits, afin d'optimiser leur conception et leur utilisation. Ici, il est question d'évaluer la performance de deux familles de géomembranes bitumineuses, l’une en bitume élastomère et l’autre en bitume oxydé, installées dans le même bassin depuis quinze ans. Les résultats permettront de fournir des préconisations d'utilisation essentielles pour les producteurs et les exploitants d’ouvrages

    Performance of geosynthetics for environmental protection in landfills

    No full text
    International audienceThe objective of this Keynote Lecture is to give an updated overview of transfer properties of geosynthetic liner materials used in landfills and of parameters that impact them. Some innovative measurement techniques are detailed, especially as regards the measurement of advective flow rates for multicomponent geosynthetic clay liners GCLs. The measurement of advective flow rates through geomembranes and multicomponent GCLs is first described. Then the effect of the mass per unit area of bentonite in GCLs, the nature of the bentonite in GCLs and of hydration without load on the hydraulic conductivity of GCLs are described. A brief presentation of pollutants of concern in landfills and especially of microorganic pollutants is given. The chemical compatibility of GCLs with leachate is discussed in the third section of this Keynote Lecture. Finally, the diffusion of organic and inorganic species in relation with the composition of leachate previously described is given in the last section of this Keynote Lecture

    Avaliação do fluxo através de barreiras. Impermeabilizantes em aterros sanitários brasileiros

    No full text
    National audienceL'article permet une quantification de l'impact de certains paramètres sur les transferts à travers les étanchéités composites de fond d'installations de stockage de déchets. Des calculs ont été effectués à partir des configurations de quatre installations de stockage de déchets brésiliens comportant une étanchéité composite. On observe à travers les résultats des calculs que le flux et la charge hydraulique sont pratiquement proportionnels. On observe également l'intérêt d'utiliser un géosynthétique bentonitique en lieu et place partiels d'une couche d'argile compactée

    Performance issues of barrier systems for landfills: A review

    No full text
    International audienc

    Evaluation de la protection contre l'endommagement des géomembranes en PEHD

    No full text
    International audienceLes géotextiles sont utilisés dans la constitution des étanchéités des Installations de Stockage de Déchets (ISD) pour protéger la géomembrane contre les effets du poinçonnement liés à la mise en oeuvre de la couche de drainage puis, en service, au poids des déchets sus-jacents. On évalue dans cette communication la performance de géotextiles non tissés aiguilletés de masse surfacique moyenne égale à 1000 g/m² à partir d'essais d'endommagement statique dans des cellules de dimensions métriques. Ces essais ont été développés antérieurement par Aufrère et al. (2009). Des préconisations sont données dans la suite en termes de longueur des fibres, module d'élasticité apparent, masse surfacique et épaisseur des géotextiles en fonction de la nature du granulat, roulé ou concassé en contact avec la géomembrane. / Geotextiles are used in the constitution of landfill lining systems in order to protect the geomembrane against puncturing effects during installation of the granular drainage layer, then during the life of the landfill site, in relation with the weight of waste. The objective of this paper is to evaluate the performance of nonwoven needlepunched geotextiles having an average mass per unit area equal to 1000 g/m² in protecting geomembrane, based on static puncture tests performed in 1m diameter cells. These tests were previously developed by Aufrère et al. (2009). Recommendations are given in the following as regards the length of fibres, the elasticity modulus, the mass per unit area and the thickness of the geotextile depending on the nature of the granular material used

    Evaluation de la réduction de capacité de débit à long terme des géocomposites due à l'intrusion du filtre

    No full text
    National audienceWater flow capacity in the plane tests were performed with 4 drainage geocomposites during 7 days with two types of contact area, either with a rigid contact area to apply the load on the geocomposite or with a flexible contact area. These tests were performed under a 200 kPa load. They allowed to evidence the influence of the type of the contact area on the hydraulic performance of the products. Thanks to this work, we could isolate and quantify the intrusion phenomenon of the filter inside the geospacer too. An approach is proposed to take into account this phenomenon on the long term design of drainage capacity in the plane of drainage composites.Des essais de capacité de débit dans le plan ont été effectués sur 4 types de géocomposites de drainage pendant 7 jours avec deux modes d'application de la contrainte : avec une interface rigide entre le géocomposite et la contrainte ou avec une interface souple. Les essais ont été réalisés sous une contrainte normale de 200 kPa. Ils ont permis de montrer l'incidence du type d'interface sur les performances hydrauliques. On a pu également isoler et quantifier le phénomène d'intrusion du filtre dans le géoespaceur. Une démarche est proposée pour traduire ce phénomène dans le dimensionnement à long terme de la capacité de débit dans le plan des géocomposites de drainage

    Influence de la masse surfacique de bentonite sur le flux à travers les géosynthétiques bentonitiques

    No full text
    International audienceLe flux et la conductivité hydraulique de neuf éprouvettes d'un même géosynthétique bentonitique ont été évalués afin de quantifier l'impact de la masse surfacique de bentonite sèche sur ces grandeurs. Les masses surfaciques de bentonite sèche du géosynthétique bentonitique étudié étaient comprises entre 3,9 et 7 kg/m². Les résultats obtenus mettent en évidence une décroissance du flux, puis une croissance, avec un minimum obtenu pour une masse surfacique de bentonite sèche proche de 5,5 kg/m². Aucune évolution significative de la conductivité hydraulique n'est observée pour des masses surfaciques inférieures à 6 kg/m². Ces résultats montrent la nécessité d'assortir la valeur de la conductivité hydraulique d'une valeur d'épaisseur fonctionnelle des géosynthétiques bentonitiques. / Flow and hydraulic conductivity of 9 specimens of a given geosynthetic clay liner were quantified in order to evaluate the effect of the mass per unit area of dry bentonite on these parameters. Masses per unit area of the specimens ranged between 3.9 and 7 kg/m². Results obtained show a decrease in flow rate followed by an increase, with a minimum obtained for a mass per unit area around 5.5 kg/m². No significant evolution of the hydraulic conductivity was noticed for masses per unit area below 6 kg/m². These results highlight the need to give simultaneously a hydraulic conductivity value and a thickness value for the geosynthetic clay liner in order to properly estimate its hydraulic efficiency
    corecore