Geosynthetics June/July 2020 - 11

Assessment of condition
of an uncovered
geosynthetic landfill
bottom liner system
By James L. Hanson and Nazlı Yeşiller

C

omposite liner systems consisting of geomembranes (GMs) placed over
geosynthetic clay liners (GCLs) commonly are used for containment
applications. Such systems are used in base liners for ponds, reservoirs,
basins and canals, and bottom and cover liner systems for landfill facilities.
Even though the use of GCL-GM composites has become commonplace in
containment systems, the long-term field performance of these systems is
not well documented or understood (e.g., NRC 2007, Benson et al. 2011).
Timely cover of the geosynthetics is critical for performance of liner
systems (Koerner 2012). Multiple problems have been identified for geosynthetic liner components under exposed conditions in the field. For
GMs, thermal stresses resulting from cyclic temperature variations cause
development of wrinkles, and UV exposure and oxidation cause aging and
degradation of the materials (e.g., Rowe 2005, Koerner 2012). Specifically,
for high-density polyethylene (HDPE) geomembranes, the service life
of the materials was estimated to decrease significantly with increasing
temperature ranging from up to 900 years at 68°F (20°C) to less than 20
years at 140°F (60°C) (Rowe 2005). For GCLs, shrinkage of GCL panels
and separation of GCL panels underneath exposed geomembrane liners
have been reported from landfills (e.g., Koerner and Koerner 2005a and b,
Thiel and Rowe 2010). Panel separations of 2 to 47 inches (50 to 1,200 mm)
corresponding to 5%-28% strain were reported for GCLs that were originally overlapped over a distance of 6 to 12 inches (150 to 300 mm) under
geomembranes along slopes with 2°-34° angles (Gassner 2009, Thiel and
Rowe 2010). The composite barriers in these cases were left exposed without
placement of overlying layers for durations between 2 and 60 months. In
addition, in a test plot with an exposed GM-GCL, migration of bentonite in
the GCL from locations near the top of slopes toward the toe of slopes was

James L. Hanson, Ph.D., P.E.,
is a professor in the Civil and
Environmental Engineering
Department at California
Polytechnic State University
in San Luis Obispo, Calif.
Nazlı Yeşiller, Ph.D., is director
of the Global Waste Research
Institute at California Polytechnic
State University in San Luis
Obispo, Calif.
All figures courtesy of the authors

www.GeosyntheticsMagazine.com

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Geosynthetics June/July 2020

Table of Contents for the Digital Edition of Geosynthetics June/July 2020

Geosynthetics June/July 2020 - Cover1
Geosynthetics June/July 2020 - Cover2
Geosynthetics June/July 2020 - 1
Geosynthetics June/July 2020 - 2
Geosynthetics June/July 2020 - 3
Geosynthetics June/July 2020 - 4
Geosynthetics June/July 2020 - 5
Geosynthetics June/July 2020 - 6
Geosynthetics June/July 2020 - 7
Geosynthetics June/July 2020 - 8
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Geosynthetics June/July 2020 - 10
Geosynthetics June/July 2020 - 11
Geosynthetics June/July 2020 - 12
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Geosynthetics June/July 2020 - 16
Geosynthetics June/July 2020 - 17
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Geosynthetics June/July 2020 - 20
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Geosynthetics June/July 2020 - Cover3
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