A “Pouch Test” for Characterizing Gas Permeability of Geomembranes

Abstract

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.

Characterizing the Gas Permeability of Natural and Synthetic Materials

“…Since the permeant concentration c mi (z, t) in the material m is much more difficult to measure than the permeant concentration c f i (t) in adjacent fluids f , Eq.2 is also often approached by considering the quantity of permeant q mi (t) which migrates from one side of the material to the other side, as a function of the difference in the concentration c f i (t) of the permeant in the adjacent fluids (Sangam and Rowe 2001;Pierson and Barroso 2002):…”

“…The relative humidity difference between both sides of the specimen is controlled and is here the driving force for water vapor migration across the specimen, resulting in a weight loss of the dish assembly. (v) The gas permeation pouch test (Pierson and Barroso 2002) consists in recording the decrease in the gas pressure inside a geomembrane pouch. It is observed that this decrease in pressure can be approached by a simple exponential law, characterized by one time constant (Barroso et al 2006), suggesting that a simplified solution of the Eq.…”

“…2 allows the characterization of non-flexible geomembranes (Pierson and Barroso 2002) and geomembrane seams (Barroso et al 2006).…”

“…A perfect circular shape cannot be obtained by the seam: the important issue is the determination of the pouch area in contact with the ambient air, which must be as precise as possible. One must also pay attention to the connection of the pouch inside to the gas supply, where the geomembrane is sandwiched and compressed between two washers through which the gas tube goes (Pierson and Barroso 2002). Figure 9 shows the linear variation over time (during the first 40 days of the test) of the quantity:…”

“…The calculation of the Peclet number (Eq. 6) with the (Lambert 1994) b Result obtained from the gas permeability pouch test, considering a pseudo steady state (Pierson and Barroso 2002) characteristics of the geomembrane specimen, the pouch geometry, and considering a maximum porosity of the geomembrane equal to 0.01, gives Pe = 5 × 10 −5 which represents the diffusive regime. Once again, this analysis highlights the advantage of using the time constant τ to compare the gas permeability of different materials instead of using permeability coefficients.…”