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Flow per Area, cm/s
40
30
20
10
0
y = 22.322x 0.457
R 2 = 0.9981
0 0.1 0.2 0.3 0.4 0.5 0.6
Level, m
Figure 5.9 Flow vs. Head for Belton Woven Fabric (not vacuumed)
root of the head. The data observed for the permeameter tests show that the actual
drainage behavior lies somewhere between these two cases. At the low heads used in
ASTM D 4491, 10-75 mm, the relationship between flow rate and head could be
approximated by a linear function.
The velocity through the fabric during the permeameter test was calculated using
the Amoco 2125 (3.3% open area), the fabric specimen area, and the permeameter flow
rate. This velocity and a pore diameter (AOS = 850 µm), were used to calculate the
Reynolds numbers shown in Table 5.8.
Table 5.8 Velocities and Reynolds Number for Flow Through Amoco Woven Fabric
Head, m Q/A, cm/s Velocity, m/s Re
0.05 1.8 0.54 459
0.1 3.2 1.0 825
0.2 4.8 1.4 1,230
0.3 5.2 1.9 1,610
0.4 7.2 2.2 1,860
0.5 8.0 2.4 2,060
0.6 8.7 2.6 2,230
The transition from laminar flow occurs in subsurface flow when the Reynolds
number exceeds 10 and in pipe flow when the Reynolds number exceeds 2,000.
Turbulent flow through a geotextile will occur when the Reynolds number is between
51