Geosynthetics February/March 2020 - 11

GEOTEXTILE FILTERS AND
RECYCLED CONTENT
Q: The final version of the ICOLD Bulletin 55
on Geotextiles as Filters in Dams is receiving
one last check for editing before being
sent for translation and publication. In that
document, your Geosynthetic Research
Institute (GRI) Report has been referenced as
a design method for estimating geotextile
service life in particular. (Thousands of
people owe you thanks.)
Two comments from the Technical
Committee on Embankment Dams were
about nomenclature and recycled materials.
The first comment on nomenclature
questioned the use of "geotextile filters"
versus "geofilters," and it is resolved to
use the former to align with International
Geosynthetics Society considerations
(but your opinion is also welcome). The
second issue is on durability and questions
to what extent the use of postconsumer
recycled polymer (polypropylene or other)
influences the durability estimate compared
to virgin material used in manufacture. Your
guidance on any quantitative response
would be highly appreciated. I have been
unable to find an appropriate reference in
the member section and apologize if I am
overlooking the obvious.
A: Regarding your questions:
1. "Geofilters" is a trademark of a commercial
manufacturer, so do use "geotextile filters,"
which is completely generic.
2. The second question is more difficult to
answer, and I take our past geomembrane
discussions to give insight. We feel that
a certain percentage of "rework" is okay
in a formulation, providing it is of the
exact same formulation and is "clean." We
ended up specifying a maximum of 10%,
although even 50% did not significantly
affect properties. Regarding "postconsumer
plastics," the variability is so great that we
decided to eliminate even a very small
percentage of this very variable material.
Hope this helps but do ask if anything is
needed at any time.

GROOVE IN THE GEOMEMBRANE
Q: We have encountered a matter that we
have not experienced before, and we are not
sure how to proceed.
We are currently building an industrial waste
facility designed with a double composite
barrier system. The barrier consists of a 60-mil
(1.5-mm) secondary double textured highdensity polyethylene (HDPE) geomembrane
and an 80-mil (2.0-mm) primary double
textured HDPE geomembrane.
During the installation of the primary
geomembrane, we noted a groove being
created during the seaming process by the
wedge welder. The installer stated that the
groove is created by the "drag bar" of the
wedge welding machine. Upon cutting open
one of the seams we see the groove is created
in both the bottom geomembrane, which
forms the base of the air channel that is later
air pressure tested, and the top geomembrane,
which forms the air channel's cover. The groove
created is approximately 0.3 to 0.5 mm deep.
The installer states that the seams pass
according to our specification because they
pass the shear and peel tests.
We are concerned because we have specified
a GRI-GM13 specification geomembrane that
calls for 80-mil (2.0-mm) thick geomembrane.
The effect of this groove, although located
within the air channel of the seam, reduced
the thickness locally to 60 mil (1.5 mm).
Unfortunately, we have picked up that this
is occurring after several panels have been
installed, and we have to make a call on
whether those seams should be cut out
and repaired or not. We have instructed the
installer to stop installation until other wedge
welding devices are brought to site that won't
cause the groove.
Have you encountered this before?
A: Most dual track wedge welders have a
follower (sometimes called drag bar or toggle)
within the recessed central portion of the
wedge. This is to be sure that the air channel is
kept open for the subsequent air pressure test.
In your case, we agree with your installer and
feel that the follower is rubbing against the
upper and lower sheet, thereby abrading the
inside air channel. Since the sheets are hot, it
doesn't take much friction to do so, and we feel
that you are seeing the resulting outcome. It is
not acceptable as you state the situation and
certainly must be remedied accordingly.

REACTION OF NEOPRENE
TO LOW-PH ACIDIC WATER
Q: Although we have numerous
geomembrane-lined lagoons containing
polluted water in the mining industry, there
are a few that contain acidic water of pH at 3.5
to as low as 2.0. In a couple of these facilities,
there is a drainage pipe penetration through
the liner system that has a make-off between
liner and pipe. Two systems of make-off are
used-either a bolted stainless steel baton
holding down the HDPE geomembrane to a
concrete make-off with a neoprene gasket
on either side of the geomembrane, or the
geomembrane is welded to a factory-formed
boot that is clamped to the pipe with a
stainless steel circular clamp. The first option
is preferred, especially for large facilities.
Are you aware of any research results that
define the durability of neoprene rubber
when exposed to low pH acidic water
(varying from arsenic acid to sulfuric acid
and occasionally hydrochloric acid)?
The follow-up question is whether it is
appropriate to provide buffer protection
by covering the exposed gasket with a
bitumastic material?
I hope to hear from you at your earliest
convenience but hope even more that we
will meet again in the not-too-distant future.
A: Regarding your question on acid reaction
of neoprene to very low pH liquids, the
closest we have to neoprene insofar as actual
data is ethylene propylene diene monomer
(EPDM) to both organic and inorganic acids
in temperatures of 100˚F (38°C) and 158˚F
(70°C). Both are thermoset plastics and the
EPDM has excellent resistance in all cases. As
a result, I think you are clear, but it is a slightly
different material.
Lastly, covering with a bituminous might
look comforting, but I don't think it's very
permanent. Otherwise, very best regards. G

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