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International audienceThe objective of this article is to propose an experimental method to compare the gas permeability of all the different materials used as gas barrier, such as compacted clay liners or geomembranes. This method is based on the falling pressure experiment, allowing the determination of a single coefficient whatever the material tested. This coefficient is the time constant τ, which is obtained by analytical solutions of the simplified equations describing the transport of gas through the material. The domain of validity is specified for porous media, thanks to a numerical solution of the complete equations system. Two applications are presented, showing the applicability of the method on compacted clay liners and on high density polyethylene geomembranes

This paper presents the results of an experimental study of various geotextiles used to filter clayey sludge. The use of geotextiles to filter clayey sludge or suspensions of fine particles in water is more complex than that for filtering suspensions of granular soils. In practice, such applications generally use flocculants to postpone the formation of a low-permeability filter cake. The objective of the present study, which does not use flocculants, is to determine how geotextile characteristics affect the capacity of the geotextile to filter clayey sludge. Three key questions are addressed: (1) What are the main differences between vertical and horizontal filtration? (2) How do geotextile characteristics (nature, opening size, permeability, etc.) affect its capacity to filter clayey sludge? (3) How do clayey sludge characteristics (i.e., grain size distribution and concentration) and the type of flow (i.e., constant head or constant flow) affect the filtering capacity of geotextiles? To evaluate the capacity of a geotextile to filter clayey sludge, we propose three relevant criteria and analyse two filtration phases induced by different cake-formation processes (controlled by the geotextile and controlled by the filter cake). To

To quantify the flow rate through multicomponent geosynthetic clay liners (GCLs), three different meter-sized specimens from different manufacturers were characterized in a dedicated experimental column. This study allows quantification of the interface transmissivity of multicomponent GCLs when the coating or attached film is damaged over an area large enough to make edge effects negligible. For all multicomponent GCLs characterized, the coating or attached film was less than 0.7 mm thick. Steady-state results indicated flow rates ranging from 4.61 ×

The objective of the paper is the presentation of a test method to quantify advective flow rates through multicomponent geosynthetic clay liners (GCLs). A procedure was developed, combining measuring devices from EN 14150 for flow rate measurement through geomembranes and a rigid wall permeameter from NF P 84-705 aiming at measuring the flow rates through GCLs. Multicomponent GCLs by structure fall between geomembranes and GCLs. The resulting testing device allows measurement of very small variations of volume with time while applying constant hydraulic pressures. The pressure difference applied on both sides of the multicomponent GCL specimens varied between 25 kPa and 100 kPa, the latter value being equal to that applied across geomembranes in EN 14150, except in one case where the multicomponent liner had a light coating. In this case hydraulic heads of 0.3 and 0.6 m were applied. Four different multicomponent GCLs were tested, from three different manufacturers, in order to determine the ability of the testing equipment to quantify the flow rate through multicomponent GCLs. The flow rate measurement was performed after a hydration phase under a very low hydraulic head and a 10 kPa normal load on the specimens in accordance with NF P 84-705. Details are given of the experimental conditions that might lead to the development of a standard for the measurement of flow rates through multicomponent GCLs. Results obtained tend to show that flow rates are one order of magnitude larger than those usually measured for virgin geomembranes, that is 10–5 m3/(m2 d), except for one of the multicomponent GCLs for which the light coating resulted in larger flow rates, measured with hydraulic heads of 0.3 and 0.6 m. In this case values consistent with previous values from the literature in the range 1.4 × 10–11 m/s to 2.2 × 10–11 m/s were obtained.

This study evaluates how alteration of geosynthetic clay liners (GCLs) affects the hydraulic behaviour of a composite liner when the geomembrane presenting a hole is overlying a GCL. Interface transmissivity experiments were performed on GCL specimens that were exhumed from field sites. The results reveal different trends in the flow rates, which decrease differently to their steady state values. The steady state flow rates obtained and the calculated interface transmissivities are of the same order of magnitude as results obtained with a virgin GCL. The transient flow rate results are discussed in relation with the GCLs parameters. Based on these results, a new equation is derived that links interface transmissivity to the hydraulic conductivity of GCLs that have been altered by the environment. Considering large transient flow rates in calculations result in a greater leakage volume penetrating the liner when compared to calculations of infiltrated volumes considering only steady state leakage volume for a period of time of 1, 10 or 30 years. From a practical point of view, this suggests the introduction of a factor of safety of 1.67 when calculating the flow rate in composite liners in order to take into account the alteration by the environment of GCLs.

In closed hazardous waste landfills, impermeable layered covers mainly composed of clays, geosynthetic clay liner (GCL) or geomembrane, etc. are used to seal in the waste to minimize water infiltration and accumulation of leachate inside the waste. An experimental site of landfill cap was realized with sodium-activated calcium bentonite GCL at a depth of 0.45 m covered by gravels and top soil. The monitoring of this site was performed during 32 months with measurements of weather conditions, and electrical resistivity tomography (ERT) and geotechnical measurements at the end of the monitoring. The two different methods underlined that the GCL’s electrical resistivity decreased after 22 months subsequent to its installation; moreover, it was possible to detect the defects that had been made in the GCL prior to closure, to simulate factors affecting GCL performance. Thereby the analyses made on the GCL samples taken at two locations in the vicinity of the ERT profile highlighted changes in the intrinsic properties of the material. Changes in the proportion of sodium and calcium cations occurred and its hydraulic conductivity increased from 5 × 10−11 to 3 × 10−6 m/s. Thus, this study shows that electrical resistivity is suitable to characterize the ageing of a GCL.

This paper presents experimental results of a study of the diffusion of phenolic compounds through two High density polyethylene geomembranes (1 and 1.5 mm thick) with a coextruded ethylene vinyl-alcohol (EVOH) inner core. The partition and diffusion coefficients were quantified for 2,4,6-tricholophenol (2,4,6-TCP), 2,3,5,6-tetrachlorophenol (2,3,5,6 TeCP), and pentachlorophenol, which are known to be toxic even at very low concentrations. The concentration dynamics in the source and receptor chambers of the diffusion cells was interpreted with the help of the numerical code POLLUTE. For partition coefficients greater than those obtained under the same conditions for a high-density polyethylene (HDPE) geomembrane, the diffusion coefficients are smaller than those for the same HDPE geomembrane. As a result, the permeation coefficient of the two coextruded geomembranes is the same order of magnitude as that of a 2-mm-thick HDPE geomembrane. Therefore, in contrast to the case for volatile organic compounds, the EVOH inner core brings no significant improvement. These results are compared to those previously obtained with volatile organic compounds for HDPE geomembranes and coextruded geomembranes.