Geosynthetics February/March 2022 - 24

Geosynthetics for solar farm development
Geogrids provide confinement and
reinforcement when properly sized aggregate
is placed above the product to develop
interlock and tensile strength. Typically,
the graded aggregate needs to be 0.5-1.5
inches (13-38 mm) to work with most
standard subgrade reinforcement geogrids.
Due to the large apertures, a geogrid does
not provide separation or filtration.
Geotextiles are permeable planar
materials that can provide reinforcement,
confinement, separation, filtration and
drainage, and they are either woven or
nonwoven (Figure 1 on pages 22-23).
Geotextiles are sometimes considered to
be weaker products; however, newer engineered
geotextiles can provide the same or
even higher tensile strengths than geogrids.
There are many different types of both
FIGURE 2 Common geogrid shapes
woven and nonwoven geotextiles, which
vary in their performance based on their
physical properties and how they interact
with the project soils (Figures 3a and 3b).
Typically, nonwoven products are weaker
and primarily used for separation and
filtration, where woven products provide
separation and filtration as well as confinement
and reinforcement.
3a
3b
FIGURES 3a and 3b Common geotextiles:
(a) nonwoven and (b) woven
Project considerations: Soil
strength analysis; extent of
geosynthetic coverage
Geosynthetic systems are installation sensitive.
The successful constructability of
the section is as important as the required
long-term capacity. For solar farms, loads
during site construction are commonly the
heaviest loads the section will experience
during its design life. Successful installation
for constructability is inherently
dependent on the soil conditions present
at the time of site-stabilization activities.
The strength of the subgrade input
to the design is an influential parameter
directly related to the required aggregate
thickness, calculated in various design
methods. Consider an analysis using the
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Geosynthetics | February March 2022
subgrade strength in terms of California
bearing ratio (CBR). Designers must
address the difference between a CBR
and a soaked CBR in their design. For
example, if the subgrade strength was
quantified by a dynamic cone penetrometer
(DCP) during a dry state, the soils
could be weaker when saturated. When
available, a soaked CBR following ASTM
D1883 (D18.05 2018) will provide designers
with a high level of confidence that the
design subgrade strength accounts for the
weak condition. Soil strength can decrease
rapidly during the first 24 hours of wetting
and will continue to decrease at a reduced
rate following the initial wetting period
(Figure 4) (Pandey and Agarwal 2019).
One possible solution to balance out a
conservative or nonconservative analysis
based on soils, which could lose strength
due to added moisture, is to provide a
" wet-weather " and " dry-weather " section
to optimize the required sections,
which would address constructability
concerns for each case (both cases would
meet long-term requirements). Having
the available method to push through
a wet-weather installation could save
money compared to that lost on potential
downtime causing project delays.
In the same effort to produce economical
site-stabilization designs, contamination
of the stabilized sections is commonly
overlooked. For most sites, it is quickly
identified that stabilization of the access
roads is required. While access roads,
parking areas or construction entrances
receive reinforcement treatment, it is common
that other areas are left untreated. On
solar farms, segmented rows of adjacent
solar panels are typically called " cells, " and
it is uncommon that there would be any
geosynthetic installed in these areas, which
would most likely return to vegetated
land following site development. During
site development, construction vehicles
(i.e., tracked equipment driving the panel
frame supports) will cause fines from the
Geosynthetics February/March 2022

Table of Contents for the Digital Edition of Geosynthetics February/March 2022
