Geosynthetics October/November 2020 - 44

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FIGURES 4a and 4b Schematic showing flag (4a) and awning (4b) configuration coupon dimensions

FIGURES 5a and 5b Coupon in (5a) flag configuration and (5b) awning configuration

FIGURE 6a, 6b and 6c Coupon after wind
whip exposure illustrating (6a) fraying, (6b)
cracking (with scrim exposure) and (6c)
wrinkling of the geosynthetic
44

the speed of sound (761.2 mph [1,225
km/h]). The rationale for this selection
is that Category 4 hurricane and F2 tornado wind speeds are approximately 100
mph (160 km/h). There is no reason to
surpass these extreme velocities when
testing geosynthetics.
Before performing any tests with the
benchtop wind tunnel, it is extremely
important to verify the performance
of the entire tunnel system, as well as
the precision and accuracy of the digital manometer; therefore, a three-part
process is to be used: 1) verification of
a calibration equation, which converts
motor voltage to wind tunnel air velocity;
2) velocity-drop and pressure-drop verification tests using a standardized flowrestrictive orifice plate; and 3) testing
of a known internal reference material
(IRM). All of these are described in detail
in GRI-GS24 "Detecting the Wind Whip
Resistance of Geosynthetics."

The wind tunnel can be set up in either
a flag (Figures 4a and 5a) or an awning
(Figures 4b and 5b) configuration.
The wind tunnel is programmed to
achieve 100 mph (160 km/h) for 1, 2,
4, 8, 16, 24 and 48 hours unless otherwise specified. The operational fluctuation should not be greater than ±5
mph (±8 km/h) over the duration of
the exposure. The coupon is removed
from the apparatus after the appropriate
number of hours of wind exposure time
for material evaluation. It is prudent
to make observations and photograph
the coupon before and after the periodic exposure times. Examples of windrelated geosynthetic damage are shown
in Figures 6a, 6b and 6c.
Test methods to be utilized for a
quantitative evaluation process for both
unexposed and exposed coupons include
ASTM D5035 Strip Tensile, ASTM D5199
Thickness and ASTM D5261 Mass Per
Unit Area. The percent retained values
for these properties can be calculated
for each exposure time and contrasted
over time.
In summary, there now exists a new
tool to evaluate index geosynthetics'
wind resistance. It allows exploration
of the new paradigm of geosynthetics
in exposed applications on a very basic
level. It does not purport to simulate
wind whip experienced by full-scale geosynthetic panels. It is likely that there
may be some significant differences in
the dynamics of full-scale experiments,
such as larger inertial forces and potentially much higher drag forces disproportional in scale to the index test being
conducted; however, this method is a
first step in conformance testing to a
specification or establishment of saturated process control (SPC) database for
materials used in such applications. G

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Geosynthetics | October November 2020

1020GS_p36-cv4.indd 44

9/22/20 1:45 AM

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Geosynthetics October/November 2020

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