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

Durability of reinforced PVC-P geomembranes installed in reservoirs in eastern Spain

[EN] The aim of this paper is to study the durability of polyvinyl chloride (PVC-P) geomembranes reinforced with a synthetic fabric in hydraulic works in the Spanish Mediterranean basin. Therefore, a set of six geomembranes installed in irrigation reservoirs for 18¿31 years were analysed. The initial characteristics of the geomembranes were determined to verify fulfilment of the Spanish regulations in force at the time. The characteristics were then assessed, and the results were interpreted with reference to the loss of plasticisers, tensile characteristics, foldability at low temperatures, dynamic impact resistance, puncture resistance, seam strength, reflected optical microscopy (ROM) and scanning electron microscopy (SEM). Additionally, the identification of the plasticisers in the geomembranes involved Fourier transform infrared spectroscopy (FTIR), gas chromatography (GC) and mass spectrometry (MS) tests. For the analysed samples, the loss of plasticisers was significant, ranging from 71.0% to 84.3%. However, the tensile strength results indicated current, regular waterproof working performances in the reservoirs. The results suggest that the durability of PVC-P geomembranes is a function of the loss of plasticisers and the state of the synthetic reinforced fibres.Blanco, M.; Touze-Foltz, N.; Pérez-Sánchez, M.; Redón-Santafé, M.; Sánchez-Romero, F.; Torregrosa Soler, JB.; Zapata Raboso, FA. (2018). Durability of reinforced PVC-P geomembranes installed in reservoirs in eastern Spain. Geosynthetics International. 25(1):85-97. https://doi.org/10.1680/jgein.17.00035S859725

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

Evaluation de l'équivalence avec des géosynthétiques bentonitiques

[Departement_IRSTEA]Eaux [TR1_IRSTEA]RIVAGEL'objectif du rapport est d'évaluer l'équivalence entre la barrière réglementaire pour les installations de stockage de déchets et une variante intégrant une géosynthétique bentonitique. Différentes configurations prenant en compte les transferts diffusifs et advectifs dans les matériaux d'étanchéité que sont géomembranes, géosynthétiques bentonitiques et argil

Géosynthétiques dans les applications minières

National audienceAprès une présentation de différentes structures à base de géosynthétiques rencontrées dans les installations minières (aires de lixiviation, zones de stockage de résidus de lixiviation ainsi que stockages de stériles), ce rapport discute des structures d'étanchéité mises en place dans ces ouvrages. On aborde ensuite la problématique du dimensionnement et de la durabilité des systèmes d'étanchéité sous les fortes contraintes mécaniques typiquement rencontrées dans les installations minières

Géosynthétiques. Un monde durable

National audienceL'objectif de ce numéro est de présenter certaines applications des géosynthétiques au service du développement durable, en évoquant la durabilité des matériaux d'étanchéité dans les ouvrages hydrauliques, dans les ouvrages pour la protection de l'environnement et en infrastructures de transport. Ces différentes études expérimentales, ainsi que l'évaluation des risques permettent de déboucher sur l'élaboration de recommandations pour une meilleure utilisation des géosynthétiques

Avis d'expert relatif à la performance hydraulique des géomembranes en polyéthylène haute densité

L'objectif du rapport d'expetise est de comparer le flux d'une géomembrane non endommagée à celui d'une couche de matériau poreux de faible conductivté hydraulique et de montrer la meilleure performance de la géomembrane tout en mettant en évidence que ce n'est pas un matériau poreux. Des recommandations sont également données en matière d'utilisation de géosynthétiques certifiés ASQUAL et de contrôle de pose

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