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

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

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

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

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

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

International audienc

Evaluation du vieillissement de deux géomembranes bitumineuses de différentes natures après 15 ans en service

10èmes Rencontres Géosynthétiques, La Rochelle, FRA, 24-/03/2015 - 26/03/2015International audienceCet article présente les résultats d'une étude expérimentale dont l'objectif est d'évaluer la performance de deux familles chimiques de géomembranes bitumineuses, l'une en bitume élastomère et l'autre en bitume oxydé, installées dans deux parties différentes d'un même bassin, après 15 ans en service. On donne tout d'abord une présentation de la différence entre les bitumes élastomère et oxydé entrant dans la fabrication des géomembranes bitumineuses. Les résultats de l'inspection visuelle des géomembranes, des mesures de flux, et l'essai d'analyse par perméation de gel (GPC) sont présentés. Dans le cas reporté ici, la performance hydraulique de la géomembrane en bitume oxydé est d'un ordre de grandeur inférieur à celle du bitumé élastomère en lien avec la fragilisation du bitume

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

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

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