Table 2. Summary of Part I results.
Standard
Standard
Flow rate
Average
deviation
Average FE
deviation
(m3m2 min1)
Test no.
Material
flow rate
flow rate
FE (%)
FE (%)
FE
1
A
0.026
71.40
5
A
0.026
0.026
3.9E6
66.69
69.6
2.5
9
A
0.026
70.56
6
B
0.026
76.11
11
B
0.026
0.026
2.8E4
73.38
72.8
3.7
12
B
0.026
68.82
4
C
0.026
54.38
7
C
0.026
0.026
8.0E5
61.08
58.7
3.7
8
C
0.026
60.52
2
D
0.026
39.19
3
D
0.026
0.026
2.9E5
48.33
45.5
5.5
10
D
0.026
48.89
Note: FE = filtering efficiency
Table 3. Summary of Part II results.
Flow rate
Final TSS
FE of system
Percent retained
(m3m2 min1)
Test no.
Geotextile?
(mg/L)
(%)
on #200 sieve
1
No
9249
95.3
did not measure
3
No
6360
96.8
1
7
No
14466
92.7
3
2
Yes
0.063
654
99.7
< 0.1
4
Yes
0.024
1185
99.4
< 0.1
6
Yes
0.120
1465
99.3
did not measure
practice of not mixing the soil and water in a
the instantaneous flow rate of water through the
blender for each test in Part II did not signifi-
geotextile--thought to be due to the destruction
cantly influence the TSS measurements of the soil
of the filter cake--was noted. The lower filtering
water mixture.
efficiency of this test compared to the other tests
with the same geotextile suggests that scraping
the downstream side of the geotextile during the
DISCUSSION
test increased the amount of soil that passed
through it. The Part II test procedure incorporated
Overview of test results
scraping the downstream side of the geotextile
In all tests using geotextiles, the water flow
because similar techniques will be used in the field
rate through the material slowed with time. This
to promote increased water flow rate across it.
probably happened because the sediment-laden
For the Part II tests, the TSS values from tests
water flowing through the geotextile formed a
without geotextiles were used to estimate the TSS
filter cake of soil particles on the upstream side
content of water that reached the geotextile. This
(LaFleur 1994, personal communication*). In test
TSS value was approximately 3.5 times that of the
2 of Part I, the downstream side of the geotextile
TSS of the water used in the Part I tests (10,025
was scraped with a spoon about 15 minutes after
mg/L vs. 2880 mg/L). However, the flow rates of
the test was begun and a significant increase in
the Part I and Part II tests with geotextiles were
similar. This most likely resulted from the prac-
tice of scraping the geotextile in Part II.
* J. LaFleur, Professor of Civil Engineering, cole
Part II test results clearly show the importance
Polytechnique, Montreal, Quebec, Canada.
6
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