Geosynthetics October/November 2020 - 24

CCR landfill final cover test pad-Part 2

in the underlying geomembrane, indicating that both geosynthetics may have
been accidentally cut through during
the exhumation. The rock beneath the
ruptured geomembrane protruded more
than 1 inch (2.5 cm) (Figure 7), exceeding specification allowance.
Subarea D excavation
Exhumation of an additional portion of
the test pad bench was performed and
observed. The geotextile and geomembrane over a subgrade protrusion were
removed and examined. Although a significant subgrade protrusion was found,
no geomembrane or geotextile damage
was observed.
FIGURE 5 Subarea F-Top of ruptured geomembrane alongside geotextile tear

FIGURE 6 Subarea F-Impression of large
rock on underside of geomembrane

material at the Subarea B excavation. The
exposed geotextile appeared to have been
previously cut to examine the underlying
geomembrane, as would be expected from
the 2016 test pad study, but the geotextile
in the area over the subgrade rocks also
had two small tears (Figure 5) that had
not been recorded during the 2016 exhumation. The remaining area of geotextile
showed no sign of damage.
After the top surface of the geotextile was examined, the geotextile was
removed. The upper surface of the IDS
geomembrane was examined, and the
IDS geomembrane was removed. The
impressions of the underlying No. 57
aggregate and one larger rock were easily
visible on the underside of the geomembrane (Figure 6). The two small ruptures
completely penetrated the geomembrane,
but there was no other detected damage
to the geomembrane, not even scratches.
Closer examination of the geomembrane ruptures indicated they may have
been cut from the topside, as evidenced
by slight scratching and burring along
the topside of the geomembrane. Also,
the geotextile tears mirrored the ruptures

2018 conclusions
and recommendations
The 2018 exhumation of the geosynthetics
further confirmed the 2016 findings. The
following conclusions were made based
on 2018 field activities:
Subgrade protrusions from scattered
No. 57 angular, crushed aggregate did not
damage the geomembrane on the slope or
on the bench with the specified installation procedures.
A subrounded stone protruding
approximately 1 inch (2.5 cm) did not
damage the geomembrane on the slope
with the specified installation procedures.
Geomembrane spikes were well
embedded into the subgrade side slope.
It is inconclusive whether the small
ruptures in the Subarea F bench geomembrane were caused by the angular subgrade rock or were from damage
caused by twice removing the overlying
materials; however, the subgrade rock
beneath the ruptures protruded more
than 1 inch (2.5 cm).
Although there were angular rocks as
large as 9 inches (22.9 cm) in dimension
in the cover soil, they generally were not
in contact with the geotextile because they

Geosynthetics | October November 2020

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Geosynthetics October/November 2020

Table of Contents for the Digital Edition of Geosynthetics October/November 2020