Geosynthetics October/November 2022 - 24

Evaluating new technologies to limit geomembrane destructive testing
pressure tolerances set in the welding
machine were adjusted to account for the
set-to-welding seaming pressure change.
Where DAW reports indicated seaming
parameters outside of the defined tolerances,
CQA personnel located and observed
the seam quality. Acceptable seam quality
was based on observing consistent welding
machine track indentations, straight alignment,
consistent geomembrane surface
appearance and cleanliness.
DAW reports at Site 1 and obserHigh
pressure
records at tee seams
were attributed
to the welding
machine passing
over three layers
of geomembrane.
vations indicated that the majority of
out-of-tolerance data were low pressures
recorded at anchor trenches, seam
ends and wrinkles; and high pressures
recorded at geomembrane tee seams.
The geosynthetic installer and CQA personnel
attributed low pressures to technicians
holding the welding machine
by its handle and lifting, guiding or
directing the machine across anchor
trenches and wrinkles. High pressure
records at tee seams were attributed to
the welding machine passing over three
layers of geomembrane.
Seam weld reports at Site 2 revealed
that pressures were constant with the
Demtech machines; however, ESI needed
more flexibility in the specified speed tolerance
window to account for increasing
sheet temperatures as the day progressed.
The project specifications were adjusted
following additional trial seam testing to
±2.5 feet/min (0.76 m/min).
Finally, both sites experienced some
difficulties with welding parameters
being set in the welding machines as a
percentage of the specified value, instead
of an absolute value. This resulted in
approximate ranges and tolerances for the
project. Trial welds showed that often the
specified tolerances could be exceeded
up to three times the project value before
seam strengths were affected. This factor
of safety built into the welding process
diminished the need for absolute tolerances
on the welding parameters.
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Geosynthetics | October November 2022
Conclusions and
recommendations
Some have questioned the need for
and value of long-established industry
standard geomembrane design and
installation CQA practices requiring
geomembrane destructive seam sampling
and testing at a frequency of one
sample per 500 feet (152 m). Practice
consistently shows that the vast majority
of destructive test results pass project
requirements.
The authors had the opportunity to
evaluate two new approaches to liner
installation through these pilot projects.
These projects aimed for destructive
testing only as the data indicates a need
by using taped geomembrane edges to
reduce seam failures due to contamination,
and by using automated welding
technology to measure and record seaming
parameters.
Based on the pilot project results, the
authors make the following conclusions
and recommendations:
* DAW seaming specifications can be
identified before the project begins;
however, field trial seams should be
conducted to affirm the actual welding
window for parameters prior
to production seaming. This gives
the installer the reasonable latitude
to adjust installation techniques to
match the site environmental and
material conditions while also providing
the engineer confidence that
the parameter ranges still satisfy the
project requirements.
* Up-front coordination is required to
make sure variable tolerances, report
setup and dissemination are coordinated.
Beginning the welding process
after these details are resolved can
prevent delays during installation
and result in higher confidence interpreting
the data results.
* The installer must be aware of and
plan for the direction of geomembrane
Geosynthetics October/November 2022

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