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Effect of interface transmissivity and hydraulic conductivity on contaminant migration through composite liners with wrinkles or failed seams

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Canadian Geotechnical Journal
Authors:
Ronald Kerry Rowe at Queen's University
Ronald Kerry Rowe
Ahmed Youssef Abdel Razek at Queen's University
Ahmed Youssef Abdel Razek
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Abstract and Figures

The leakage and the peak chloride concentration in an aquifer for a single composite liner facility is modelled for (i) a hole in a geomembrane wrinkle and (ii) a failed seam. A method using a closed-form solution to calculate leakage together with a l½-dimensional (l½D) semi-analytic contaminant transport model is proposed, and the results compared with those obtained from two-dimensional (2D) finite element modelling (FEM). Leakage is shown to be highly dependent on the interaction between the interface transmissivity (θ) and hydraulic conductivity beneath the wrinkle (kb). Similar leakages arising from different combinations of transmissivity and hydraulic conductivity are shown to have significantly different impacts on an underlying aquifer. Contaminant transport modelling is needed to assess this effect for the likely range of uncertainty regarding interface transmissivity (θ) and hydraulic conductivity. The 2D FEM is conceptually more comprehensive; however, using conventional software only a very limited size of problem could be accurately modeled given the greatly different scales that must be modelled. In contrast, the semi-analytic 1½D approach readily allowed consideration of the highly variable scales, and gave results at the down-gradient edge sufficiently similar to the 2D approach.
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ARTICLE
Effect of interface transmissivity and hydraulic conductivity
on contaminant migration through composite liners with
wrinkles or failed seams
R. Kerry Rowe and A.Y. AbdelRazek
Abstract: The leakage and the peak chloride concentration in an aquifer for a single composite liner facility is modelled for (i)a
hole in a geomembrane wrinkle and (ii) a failed seam. A method using a closed-form solution to calculate leakage together with
a l½-dimensional (l½D) semi-analytic contaminant transport model is proposed, and the results compared with those obtained
from two-dimensional (2D) finite element modelling (FEM). Leakage is shown to be highly dependent on the interaction between
the interface transmissivity (
␪
) and hydraulic conductivity beneath the wrinkle (k
b
). Similar leakages arising from different
combinations of transmissivity and hydraulic conductivity are shown to have significantly different impacts on an underlying
aquifer. Contaminant transport modelling is needed to assess this effect for the likely range of uncertainty regarding interface
transmissivity (
␪
) and hydraulic conductivity. The 2D FEM is conceptually more comprehensive; however, using conventional
software only a very limited size of problem could be accurately modeled given the greatly different scales that must be
modelled. In contrast, the semi-analytic 1½D approach readily allowed consideration of the highly variable scales, and gave
results at the down-gradient edge sufficiently similar to the 2D approach.
Key words: geosynthetics, contaminant migration, landfill, interface transmissivity, composite liner.
Résumé : La fuite et le pic de concentration de chlorure dans un aquifère pour une seule installation de revêtement composite
sont modélisés pour (i) un trou dans une ride de géomembrane, et (ii) un joint défectueux. Une méthode utilisant une solution
sous forme fermée pour calculer les fuites avec un modèle de transport de contaminants semi-analytique en l½ dimensions (l½D)
est proposée, et les résultats sont comparés à ceux obtenus par la modélisation par éléments finis (FEM) en deux dimensions (2D).
Il a été démontré que les fuites dépendent fortement de l’interaction entre la transmissivité de l’interface (
␪
) et la conductivité
hydraulique sous la ride (k
b
). Des fuites similaires résultant de différentes combinaisons de transmissivité et de conductivité
hydraulique ont des impacts significativement différents sur un aquifère sous-jacent. Une modélisation du transport des
contaminants est nécessaire pour évaluer cet effet dans l’intervalle d’incertitude probable concernant la transmissivité de
l’interface (
␪
) et la conductivité hydraulique. Le modèle FEM 2D est conceptuellement plus complet, mais avec un logiciel
conventionnel, seule une taille très limitée de problème pourrait être modélisée avec précision, étant donné les très différentes
échelles à modéliser. En revanche, l’approche semi-analytique l½D permettait aisément de prendre en compte les échelles très
variables et donnait des résultats au niveau du bord descendant suffisamment similaire à l’approche 2D. [Traduit par la
Rédaction]
Mots-clés : géosynthétiques, migration des contaminants, décharge, transmissivité d’interface, doublure composite.
1. Introduction
Geomembranes (GMBs) are often used in conjunction with a
geosynthetic clay liner (GCL), a compacted clay liner (CCL) or both
to form a composite liner for a wide range of hydraulic contain-
ment applications (Shackelford et al. 2010;Rowe 1998,2005,
2012a;Rowe et al. 2004,Bouazza 2010). When a GMB is exposed to
heating due to solar exposure, it experiences wrinkling (e.g.,
Giroud and Peggs 1990;Giroud and Morel 1992;Pelte et al. 1994;
Giroud 1995;Rowe 1998;Koerner et al. 1991;Touze-Foltz et al.
2013;Chappel et al. 2012a,2012b;Rowe et al. 2012). Wrinkles can
vary in length; smaller wrinkles can also interconnect with larger
ones forming a continuous network of wrinkles. If a hole develops
in, or adjacent to, a wrinkle in a GMB, it becomes a major conduit
for leakage through a composite liner (e.g., Brachman et al. 2007;
Rowe 2012a). GMB panels are welded together, often using the
dual wedge technique. These welds, or the heat-affected zone im-
mediately adjacent to the weld, represent a particularly vulnera-
ble point due to a combination of magnified tensile strains at this
location (relative to the sheet away from the weld; e.g., Giroud
2005;Peggs et al. 2014;Kavazanjian et al. 2017) and due to accel-
erated aging of some welds relative to the sheet (Rowe and Shoaib
2017,2018). As there is likely to be more than 1500 m/ha of welds
between panels, a failure in the seams can be an important source
of longer-term leakage through composite liners.
In a composite liner with a GMB over a GCL, the hydraulic
conductivity (k) of GCL and interface transmissivity (
␪
) of GCL–
GMB are the two key hydraulic parameters required for calculat-
ing leakage through the liner system and hence the contaminant
impact on an underlying aquifer (e.g., Rowe 2012a). The hydraulic
conductivity (k) is affected by confining stress, hydration before
Received 20 September 2018. Accepted 1 December 2018.
R.K. Rowe* and A.Y. AbdelRazek. GeoEngineering Centre at Queen’s–RMC, Queen’s University, Kingston, ON K7L 3N6, Canada.
Corresponding author: R. Kerry Rowe (email: kerry.rowe@queensu.ca).
*R.K. Rowe currently serves as an Associate Editor; peer review and editorial decisions regarding this manuscript were handled by C. Lake.
Copyright remains with the author(s) or their institution(s). Permission for reuse (free in most cases) can be obtained from RightsLink.
1650
Can. Geotech. J. 56: 1650–1667 (2019) dx.doi.org/10.1139/cgj-2018-0660 Published at www.nrcresearchpress.com/cgj on 3 December 2018.
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