Geosynthetics April/May 2023 - 32

Geosynthetic clay liners: An effective and efficient solution
GCLs are also much quicker and
easier to install, which reduces labor
costs and speeds up the time to get the
facility operational. The same 35-acre
(14-h) area would have taken almost a
whole construction season to install a
compacted clay liner in 6-inch (15.2-cm)
lifts. The installation of the GCL took
two to three months with a standard
nine-member liner installation crew.
This timeline also included the installation
of the HDPE, which took place
simultaneously, as the GCL had to be
covered every day by the geomembrane.
Process
To expedite the heap leach pad installation,
Haley & Aldrich prepared an engiA
crew deploys geomembrane on top of GCL on a heap leach pad.
GCLs have a total thickness of less
Lixiviant addition
Liner
system
Lixiviant
Pond
GM GCL
Berm
Ore
heap
Foundation
soil
Schematic depicting a cross section of a
typical composite liner heap leach pad. A
lixiviant solution is applied to the ore heap
dissolving the desired metal. The pregnant
leachate solution is then captured in a
collection pond and refined.
than 1 inch (2.5 cm) and provide better
hydraulic performance than several
feet of compacted clay. A fully hydrated
GCL typically has a permeability approximately
20 times lower than a standard
compacted clay liner.
Resistant to varying weather conditions,
GCLs are less likely to be affected
by freeze-thaw or desiccation-rewetting
cycles. Freeze-thaw cycles frequently
cause compacted clay liners to crack and
lead to leakage. Unlike compacted clay
liners, a geosynthetic clay liner provides
consistent performance and is not subject
to performance decreases resulting
from varying moisture content, density
or clay content.
GCLs are an ideal alternative to clay
liners because they require significantly
less installation effort than a compacted
clay liner. One truckload of GCL is equivalent
to 150 truckloads of compacted clay,
thereby using up fewer natural resources.
32
Geosynthetics | April May 2023
neering design change (EDC)-that is, a
" minor change " requiring state regulatory
review and approval. The firm proposed
use of the GCL in select areas so
that the EDC was uncomplicated. It also
had to modify project details since the
GCL was 11.8 inches (30 cm) less thick
than the original proposal of 12 inches
(30.5 cm) of low permeability soil.
The largest regulatory hurdle was the
slope stability analysis. The heap leach
pad was mostly flat with a slight slope on
the sides. Haley & Aldrich, armed with
its library of previous projects documenting
slope stability, was able to provide
a slope stability analysis for the owner
readily and concisely, speeding up agency
regulatory review. Project-specific testing
was performed concurrently with the
EDC submission to confirm the design
calculations. Approval from the state was
granted within approximately one week.
Another advantage in the switch to
GCL was the availability of an experienced
installation crew that had the ability
to install both the GLC and the more
technically challenging HDPE membrane.
International Lining Technologies
of Reno, Nev., has an outstanding
Geosynthetics April/May 2023

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