Geosynthetics February/March 2021 - 26

Comparative analysis of the flow and filtration capabilities of sediment retention devices

by combining water and soil in the
upstream mixing tank and agitating for
one minute prior to initiation of the test.
In the test method, it is prescribed that
13.3 gallons (50 L) of water and 0.33
pound (0.15 kg) of the prescribed soil
should be mixed and introduced to the
upstream face of the SRD. The soil can
be either site-specific or a default silty
clay. The silty clay soil prescribed in the
standard test method shall conform to
the target gradation shown in Figure 3
and shall have a plasticity index (PI) ≤
15. During the test, the sediment-laden
flow passing through the installed SRD
is collected, and the total time required
for the entire influent volume to pass
through the SRD is recorded. After the
completion of the test, vacuum-assisted
filtration of the collected effluent seepage is used to obtain the mass of the
sediment that was able to pass through
the SRD. Vacuum-filtered sediments
FIGURE 3 ASTM D5141 prescribed target soil gradation

Percent Passing

Sieve Size (opening size, mm)

100

No. 10 (2.0 mm)

80-100

No. 40 (0.420 mm)

70-90

No. 100 (0.149 mm)

50-70

No. 200 (0.075 mm)

FIGURE 4 ASTM D7351 apparatus schematic

Geosynthetics | February March 2021

are dried and weighed, and the weight
of collected sediment is compared to
the initial influent amount of sediment
put into suspension to determine the
filtering efficiency. In addition, the
total time required for the entire influent volume to pass through the SRD
is used to calculate a flow rate, represented in gallons per minute per square
foot (m3/min/m2).
Summary of test method
ASTM D7351
ASTM D7351 is a standard full-scale
performance test commonly used to
characterize installed SRD system performance, including sediment and flow
retention, and structural behavior under
hydraulic loading. Sediment-laden water
is allowed to flow up to and through
an installed SRD. At a minimum, the
amount of sediment-laden flow and
associated sediment passing through
the SRD is measured. The measurement of flow (seepage) and sediment
that passes through the SRD subtracted
from the amount in the upstream flow,
and then divided by the amount in the
upstream flow, is used to quantify the
water-retention percentage and filtration-effectiveness percentage of the SRD
under full-scale conditions.
This test method may also assist
in identifying physical attributes of
the SRD system that contribute to its
sediment control performance, and it is
useful for comparison of different SRDs
and their unique installation requirements. In contrast to ASTM D5141,
D7351 evaluates the " as installed " SRD
system performance. This is an important difference in the test methods. As
an example, a silt fence system with
a low-flow, high-sediment-retention
filtration component would require
robust post size and frequent post spacing, as the filtration component will
retain a high volume and, consequently,

Geosynthetics February/March 2021

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