Geosynthetics February/March 2023 - 9

TRANSITIONING FROM 30 MIL PVC
GEOMEMBRANE TO 60 MIL HDPE
Q: I have a client that operates a Subtitle C
landfill that utilizes a double-liner system
of 30 mil (0.76mm) PVC geomembrane for
the base liner. They are wanting to evaluate
the possibility to transition from 30 mil (0.76
mm) PVC to 60 mil (1.52 mm) high-density
polyethylene (HDPE) geomembrane for the
base liner system. In your opinion, what is the
best way to transition from 30 mil (0.76 mm)
PVC geomembrane to 60 mil (1.52 mm) HDPE
geomembrane? Is there a way to seam or
mechanically attach 30 mil (0.76 mm) PVC
to 60 mil (1.52 mm) HDPE?
A: We are asked this question often. Most
county landfills in the United States switched
from PVC to HDPE liners in the early 1990s.
They are often faced with joining dissimilar
materials at the longitudinal edge of an old
to new cell. We have seen this done with twosided
tape, adhesives and geosynthetic clay
liner (GCL) between the PVC and the HDPE.
The area to be bonded is generally oversized
100 mm to 300 mm and is usually on the
flat top of an intermittent berm. However,
there are several regulators who do not like
this marginal type of seaming. They want
positive fixity and load transfer. This can be
accomplished by circa 1970 interlocking pipe
section buried in anchor trench technique,
pioneered by Clifford Gundle in South Africa
as seen in the picture below. It is onerous,
expensive and time consuming but still
works well. Be careful ... if the PVC is brittle
and has lost its flexibility, do not attempt this
method. You will do more harm than good.
Sieracke, " M. " and Peggs, " I. " (2013). " Thermal Seaming
of Polyethylene Geomembranes. " Page 65-81
Proceedings from. GRI-25 Conf., Long Beach, Calif.
GEOMEMBRANES WITH
BETTER PERFORMANCE
STRENGTH REDUCTION
OF GEOGRIDS USED IN
REINFORCED WALLS
Q: We are researching liner alternatives
for an industrial client that will have lined
impoundments subject to high temperature
influent (>140 degrees F), low pH (1 SU+/-),
and may have organic contaminants. Are
there any polyethylene geomembranes that
meet these requirements?
A: Thank you for your question about
geomembranes with better performance
than GRI GM13 GMB materials. There are
several geomembranes that meet these
requirements, which are regularly discussed.
They are all produced with bimodal
polyethylene resins.
1. Solmax's High-Temperature HDPE
geomembranes are engineered to provide
exceptional quality, chemical resistance
and service life in prolonged exposure
to temperatures up to 212°F (100°C).
2. Layfield's HeatGard product, which
is a new high-temperature HDPE
geomembrane produced from bimodal
polyethylene resins.
3. Naue's Carbofol HDPE geomembranes.
Manufactured using high quality
polyethylene resins. Carbofol is
manufactured in various thicknesses
and up to 7.50 m width.
4. ATARFIL'S HD is a geomembrane (GMB)
manufactured from verified top-quality
high-density polyethylene (HDPE) resins
to meet the most stringent usage.
These materials were commercialized in late
2018. They have had good success in hot
brine containment, secondary liner under
heated tanks, leachate recirculation landfills,
hot potable water containment, mining heap
leach, ponds and long-term chlorinated
water immersion. These geomembranes
feature long life at high temperatures,
superior halogen and hydrocarbon
resistance, and excellent chemical resistance
to low pH solutions. I recommend that you
consult Mills and Beaumier (2017) for specific
details about geomembranes made from a
bimodal resin.
Mills, A., and Beaumier, D. (2017). " Long-term
performance of HDPE geomembranes exposed to high
service temperature. " ASCE Geotechnical Frontiers,
Orlando, Florida.
FIGURE 1 First Polyethylene Seam (Courtesy
Clifford Gundle) ref. Sieracke and Peggs
Q: At the moment there are two issues
that create uncertainty with the use of PET
fabrics and geogrids in the Netherlands.
First, for many years we built pile-supported
geosynthetic reinforced embankments (socalled
piled mattresses to reduce settlements
under embankments on soft soils). The fill is
supported by a geosynthetic mat, which rests
on top of the pile (caps). The fill on top of the
PET geosynthetics is mostly made of crushed
concrete and stone granulate. This fill can
have very high pH values due to the crushed
concrete part. This high pH value could have
a negative impact on the long-term strength
of the PET due to hydrolysis. Do you have a
recommendation for this issue? The second
point is about the reduction in strength of
geogrids that are used in reinforced walls.
In our case, the front of such a wall is made
of concrete panels. The space between
the panels of some concrete units is wide
and left open. In this space there is no UV
protection, which means that the strength of
the geogrid will reduce in time. The geogrid is
a PET geogrid with coating. Do you have any
information from GSI's mechanically stabilized
earth (MSE) wall database that indicates if and
how quickly reduction of strength due to UV
could develop in such a case?
A: Nice to hear from you. I would recommend
the following reference, Soleimanbeigi, A.,
Tanyu, B. F. Aydilek, A. H. and Florio, P. (2019),
" Evaluation of recycled concrete aggregate
as backfill for geosynthetic-reinforced MSE
walls, " Geosynthetics International 26(4):1-50,
DOI:10.1680/jgein.19.00025. The story is not
good when the pH gets near 11, particularly
when you are dealing with poor-quality
(uncoated, low molecular weight) polyester.
Regarding your second question, we have
not seen this failure mechanism (near face
UV degradation) in any of our 403 MSE
failures that we have investigated for the
GSI database, which dates back to 1987. If
it is a possible failure mechanism, however,
it is new to us and we have not deemed it a
trigger in any of our case histories. This might
be an area for future investigation. G
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Geosynthetics February/March 2023

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