evaluation of belted strand retention fabric and ... · pdf filestudied silt fence using...
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Evaluation of Belted Strand RetentionFabric and Conventional Type C Silt
Fence using ASTM standards
Dr. Mark RisseDr. Sidney Thompson
Xianben ZhuKeith Harris
Department of Biological and Agricultural Engineering
Introduction
Users of erosion and sediment control (ESC)products have difficulty of comparing theperformance of different products and techniques.Few methods available for evaluating differentproducts for approval by State agencies.Different test procedures make it hard to compareresults
Literature reviewSome standard tests available
WisDOT (Several Categories)ECTC and North American Stormwater andErosion Control Association are working onproviding test procedures and standards. Labsapproved for testing of erosion mats:
– Colorado State University– San Diego State University– E-Lab, American Exclesior Inc.– Texas Transportation Institute's Hydraulics, Sedimentation, and
Erosion Control Laboratory
• Not Many Procedures for testing Silt Fence
• Wyant(1980) conducted a comprehensive study onsilt fence, which led to development of ASTMD5141 (Filtering Efficiency and flow through)
• Both Kouwen(1990) and Barrett et al. (1995)studied silt fence using different procedures, bothconcluded that deposition from the large pondedvolume created by the fence was the mainmechanism for sediment removal.
• Thiesen(1992) suggested that the Apparent OpeningSize of the fabric determines the amount of storagecapacity of the fence.
• Thomas Carpenter and Joel Sprague creatednew procedures for testing the effectivenessof sediment retention device. Primarilylooking at installation practices.
• Most State agencies look at materialproperties including strength of fabric,opening size, and
flow rate.
Objective
• To test the filtering efficiency and flow rate ofBelted Strand Retention Fencing (SiltSaver) andType C silt fence using ASTM standard D5141
• To evaluate the effectiveness of this new fencematerial.
• Not approved in Georgia due to low flow rate andnot meeting strength specifications.
Procedure 1
• Flume constructed
according to ASTM
standard. (85x125 cm)
• Flume set at a 8% slope
• 50 L of mixture added to
top.
• Collect all effluent.
Procedure• The first run sediment free water
• Second run was a 2890 ppm (standard) concentration ofsediment laden water.
• A 3rd run with a 5780 ppm (Double) concentration wasrun on the same fence.
• Total time of flow was recorded to 20 minutes.
• Subsamples of the sediment laden water and the filtratewere taken for analysis.
• Procedure was replicated three times for each fence.
• Three different soils, Sand, Clay, Silt Loam
Results: Flow Rate
• Equations in Standard report flow rate inm3/m2/min.
• Errors in equations which are beingcorrected by ASTM.
• We report both the standard measurementand simply L/min.
Clear Water Flow RateAverage Blank Flow
0.5120
0.4235
0.0000
0.1000
0.2000
0.3000
0.4000
0.5000
0.6000
BSRF Type C
Fence Type
F2
0 (
m3/m
2/m
in)
No significant difference
Flow Rate
Standard Concentration
4.20
1.37
9.58
1.93 2.001.19
0.00
2.00
4.00
6.00
8.00
10.00
12.00
Sand Silt Loam Clay Loam
Soil Type
Av
g fl
ow
ra
te (L
/min
)
BSRF
Type C
Standard Concentration
0.0022 0.0023
0.0470
0.0014 0.0016
0.1072
0.0000
0.0200
0.0400
0.0600
0.0800
0.1000
0.1200
Sand Silt Loam Clay Loam
Soil Type
F2
0 (
m3/m
2/m
in)
BSRF
Type C
Type C had higher flow rate with sediment.
Flow rate much lower on siltand clay.
Flow RateDouble Concentration
0.0015 0.0005 0.00050.00210.00150.0098
0.0000
0.0200
0.0400
0.0600
0.0800
0.1000
0.1200
Sand Silt Loam Clay Loam
Soil Type
F2
0 (m
3/m
2/m
in)
BSRF
Type C
Double Concentration
0.47 0.45
2.08
1.33 1.31
1.78
0.00
0.50
1.00
1.50
2.00
2.50
Sand Silt Loam Clay Loam
Soil Type
Av
g f
low
ra
te (
L/m
in)
BSRF
Type C
Flow rates lower at double conc.
Less difference betweensoil types.
Flow Rate Conclusions• The type C silt fence had higher average flow rates
for all soil types in both the standard (2890 ppm)and double (5780 ppm) concentrations but not theclear.
• BSRF had a more than 60% reduction in flow ratewhen running a double concentration after thestandard concentration for finer textured soilswhile the type C had less than 35% reduction.
• Sediment on the fence appeared to influence flowrate.
Suspended Solids (Ss) and FilterEfficiency (Fe)
• Standard states that only Filtering Efficiency should
be reported.
• We report Efficiency and Suspended Solids
concentration and Turbidity of effluent.
• With low slope, considerable amounts of sediment
settled out prior to even reaching the silt fence.
Suspended Solids in Effluent
Double Concentration
73.3
166.7163.0
608.7
509.3
139.3
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
Sand Silt Loam Clay Loam
Soil Type
Av
g.
Su
sp
en
de
d S
oli
ds
(p
pm
)
BSRF
Type C
Standard Concentration
76.792.3
300.7
161.3
46.0
365.7
0.0
100.0
200.0
300.0
400.0
500.0
600.0
700.0
Sand Silt Loam Clay Loam
Soil Type
Av
g.
Su
sp
en
de
d S
oli
ds
(p
pm
)
BSRF
Type C
Standard Concentration
94.4
97.396.8
87.3
89.6
98.4
75.0
80.0
85.0
90.0
95.0
100.0
Sand Silt Loam Clay Loam
Soil Type
Fil
ter
eff
icie
nc
y
BSRF
Type C
Double Concentration
97.5
94.295.294.4
78.9
82.4
75.0
80.0
85.0
90.0
95.0
100.0
Sand Silt Loam Clay Loam
Soil Type
Fil
ter
eff
icie
nc
y
BSRF
Type C
Filter Efficiency
Turbidity
Double Concentration
43.3
92.7
138.3
77.0
452.7
359.3
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0
450.0
500.0
Sand Silt Loam Clay Loam
Soil Type
Av
g.
turb
idit
y (
NT
U's
)
BSRF
Type C
Standard Concentration
43.3
167.0
220.7
77.7 83.2
25.5
0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0
450.0
500.0
Sand Silt Loam Clay Loam
Soil Type
Av
g.
turb
idit
y (
NT
U's
)
BSRF
Type C
Results for Filtering Efficiency• The BSRF proved more efficient at removing
suspended solids and turbidity for all soil types atboth the standard and double concentration runs.
• BSRF reduced suspended solids values 2 to 3 timeslower than the type C fence.
• BSRF retained its filtering efficiency for the doubleconcentration while the
type C lost 12 to 15% of
its efficiency on the finer
textured soils.
• Turbidity results mirrored
the Suspended Solids data.
• Both fence materials had
high filtering efficiencies.
Modifications to Standard• Since Filtering efficiency was high and significant
settling occurred prior to the fence, an additional test
was conducted with the flume set at a 58% slope.
• We also wanted to examine the influence of higher
hydraulic heads on the various fence materials since
this would be important to field applications.
• Same procedures were used.
• Three replicates of the silt loam soil were conducted
for each fence material.
1.941.95
3.59
1.57
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
Standard Double
Concentration
BSRF
Type C
Flow Rate @ 58% slope
• The higher relief resulted in a greater flow rates for bothfence materials. The BSRF fence under high reliefconditions exhibited higher flow rates at both the standardand double concentrations.
447.40474.23
289.87
860.07
0.00
100.00
200.00
300.00
400.00
500.00
600.00
700.00
800.00
900.00
1000.00
Standard Double
Concentration
BSRF
Type C
84.5283.59
89.97
70.24
60.00
65.00
70.00
75.00
80.00
85.00
90.00
95.00
Standard Double
Concentration
BSRF
Type C
BSRF was more efficientthan the type C though thedifferences were lesspronounced then 8 % slope.
Performance @ 58%
Suspended solidswere higher and efficiencies lower for both fences.
One additional test of effectiveness
• Flume is expensive toconstruct.
• We tested a new apparatusthat could be used to testsimilar properties.
• 5L of water with samesediment conc.
Results
• Flow rates were similar between BSRF (0.27L/min) and Type C (0.22 L/min) although theType C had a slightly higher clear water flowrate (22 to 19 L/min).
• BSRF had a higher filtering efficiency (95%to 88%) and percent reduction in turbidity(82% to 60%) than type C fence materials.
• These results were comparable to the flumetest results at 8%.
30 degree sidewalls, 4 ft post spacing
Hydrostatic load of 8 inches
Finite Element grid: 2 inches
Modeling of Loads on fence
Strength Conclusions• BSRF fence withstood loads that would normally
be encountered in the field.
• While the fabric did not meet GA DOT specs fortensile strength or deflection, the design appearsadequate.
• Biodegradable design offers environmental andsafety benefits that should be considered.
• Modeling led to design improvements.