Influência da natureza da bentonita na transmissibilidade da interface entre geomembrana e GCL de barreiras compostas

National audienceLes géosynthtéiques bentonitiques (GSB) sont des matériaux géosynthétiques généralement formés par un ou deux géosynthétiques et de la bentonite qui peut être de différentes natures en fonction des cations interfoliaires majoritairement présents. On peut distinguer les calciques naturelles, les sodiques naturelles et les calciques activées. Lorsqu'elles sont confinées et hydratées les bentonites possèdent une très faible conductivité hydraulique . De plus, d'après la littérature, la conductivité hydraulique des GSB dépend justement de la nature de la bentonite qu'ils contiennent.Les GSB contenant de la bentonite sodique ont généralement une conductivité hydraulique plus faible que ceux contenant de la bentonite calcique. C'est pourquoi on a cherché à investiquer l'effet que pouvait avoir la nature de la bentonite sur le comportement hydraulique des étanchéités composites, et sur la transmissivité d'interface géomembrane - GSB en particulier. Différentes conditions de charge hydraulique et de contraintes mécaniques ont été simulées. On a pu vérifier que malgré des différences significatives de conductivité hydraulique des GSB, l'impact sur la transmissivité d'interface est faible

Flux de liquides au travers des étanchéités composites d'installations de stockage de dechets. influence des caractéristiques du GSB

National audienceL'objectif de ce chapitre est de faire le point de l'état de l'art et des dernières connaissances relatives au comportement hydraulique des étanchéités composites géomembrane-GSB, en particulier en fonction de la nature de la bentonite contenue dans les GSB. On tire des préconisations pour le choix des matériaux à utiliser in situ en fonction de résultats d'essais de laboratoire

Influence de la nature de la bentonite dans les GSB sur les transferts advectifs dans les étanchéités composites géomembrane-GSB

International audienceThe flow rates along the interface between damaged geomembranes (GM) and geosynthetic clay liners (GCL) placed on top of a compacted clay liner (CCL) were measured by means of laboratory tests performed with an apparatus especially designed for this purpose. The tests performed aimed at verifying the influence of the structural and material properties of the GCL on the transmissivity along the GM-GCL interface and flow rates through composite liners. Four types of GCLs with two different bonding processes (stitch-bonded or needle-punched) and different bentonites (natural sodium or natural calcium) were tested. The results obtained showed no significant differences among flow rate versus time in most of the tests performed, especially after the steady-state conditions of flow were reached. An analytical solution was employed to estimate the transmissivity of the GM-GCL interfaces. This solution also allowed predictions of flow rates and radius of wetted areas for typical configurations of composite liners in the field. The results obtained showed little influence of the nature of the bentonite and the predominance of the presence of preferential flow paths between the geomembrane and the GCL surface on the transmissivity of GM-GCL interfaces and flow rates through composite liners

Influence of structural and material properties of GCLs on interface flow in composite liners due to geomembrane defects

International audienceThe flow rates along the interface between damaged geomembranes (GM) and geosynthetic clay liners (GCL) placed on top of a compacted clay liner (CCL) were measured by means of laboratory tests performed with an apparatus especially designed for this purpose. The tests performed were aimed at verifying the influence of the structural and material properties of the GCL on the transmissivity along the GM–GCL interface and flow rates through composite liners. Four types of GCLs with two different bonding processes (stitch-bonded or needle-punched) and different bentonites (natural sodium or natural calcium) were tested. The results obtained showed no significant differences among flow rate versus time in most of the tests performed, especially after the steady-state conditions of flow were reached. An analytical solution was employed to estimate the transmissivity of the GM–GCL interfaces. This solution also allowed predictions of flow rates and radius of wetted areas for typical configurations of composite liners in the field. The results obtained showed little influence of the nature of the bentonite and the predominance of the presence of preferential flow paths between the geomembrane and the GCL surface on the transmissivity of GM–GCL interfaces and flow rates through composite liners

Characterisation of permeability to gas of geosynthetic clay liners in unsaturated conditions

International audienceThis paper is a contribution to the characterisation of permeability to gas of unsaturated GCLs, with applications in cover liners of municipal solid waste landfills. Conducting such tests at low gas pressure gradient limits the risk of moisture distribution change in the bentonite, which has been observed under high pressure gradients. However, a consequence of a low pressure gradient is a small gas flow rate that is difficult to measure with good accuracy. Therefore a solution may be the use of transient state tests, such as the falling pressure test adapted to GCL permeability characterisation. This paper shows the influence of the main parameters related to the test, and to the material tested (natural or activated calcium bentonite, moisture content, presence or not of small cracks in the bentonite). The results obtained showed good repeatability for gas differential pressures up to 40 kPa for the test conditions employed in this work. The results showed that the gravimetric moisture content of the GCL necessary to attain a certain permeability value depends on the nature of the bentonite, which was not observed in terms of volumetric moisture content. However, other factors were shown to be more important than the nature of bentonite in GCL permeability to gas: the desiccation due to the gas flow can significantly increase the permeability, which compromises the GCL's performance as a gas barrier