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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

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Wrinkles frequently appear in geomembranes exposed to solar radiation. In 1992, Giroud and Morel established a model to predict the wrinkle geometry according to the temperature and thermal characteristics of the geomembrane. The aim of this paper is to throw some light on the thermal behaviour of geomembranes subjected to thermal radiation. The overall heat exchange coefficient with the surroundings, the absorption coefficient and the coefficient of thermal expansion were measured in different conditions for several geomembranes made of polyethylene and polyvinyl chloride. The results show the effectiveness of a white coating on geomembranes as a protection against solar radiation. A finite-difference model was developed to predict the geomembrane temperature in relation to the overall heat exchange coefficient, the absorption coefficient and the meteorological conditions. Results obtained tally closely with laboratory and in-situ measurements. It appears that the proposed model could be used in conjunction with the one developed by Giroud and Morel, which was also checked on the same experimental site.

To characterize the gas permeability of seamed or non-seamed geomembranes, laboratory tests were carried out using a new permeability test: the gas permeability pouch test. Circular and rectangular “pouches” made of two pieces of high density polyethylene (HDPE) geomembrane were tested. To study the permeability of the geomembrane itself, the pouch was made of two circular geomembrane sheets welded together (the percentage of the seamed area is negligible compared to the non-seamed area). To study the permeability of the HDPE seams, two rectangular pieces of geomembrane were welded together using the thermal-hot dual wedge method (where the percentage of the seamed area is predominant). For this test, specimens are pressurized with a gas (e.g., nitrogen, in this case), and immersed either in air or in water. The flow of gas is indicated by a decrease in the pressure inside the pouch. The test results obtained are in agreement with results reported in the literature and show that the gas permeability pouch test can be used to characterize geomembrane permeability, with the advantages of being easy to carry out and allowing the assessment of the seam quality by quantitative measurement of their permeance.