discharge capacity of prefabricated vertical drains confined in clay

MIURA AND CHAI D Discharge Capacity of Prefabricated Vertical Drains Confined in Clay
(Miura et al. 1998). Furthermore, no air bubbles were forced out when the hydraulic
shocks were applied for the tests on PVDs A and C.
The filter opening size and geometry of the drainage channels may have an effect
on the clogging phenomenon. The apparent opening size (O 95 , the filter opening diameter
such that 95% of the openings are smaller that that size) of the four filter types was
measured using glass beads according to ASTM D 4751. The apparent opening size distributions
of the four filters are given in Figure 9, and the O 95 values are listed in Table
2. Even though it is not generally agreed upon to use O 95 values to represent the opening
size of nonwoven geotextiles, i.e. filters (Giroud 1996), it is believed that O 95 values
are a useful index for comparing the relative size of the 5%-larger geotextile openings.
Table 2.
The O 95 values of the PVD filters and the geometry of a unit drainage channel.
Test
no.
PVD
O 95 of
filter (µm)
Geometry of unit
drainage channel
Cross-sectional
area (mm 2 )
Shape
factor (mm)
t filt d f ti C
Q C
Area reduction due
to filter deformation
(%)
Q R
3months
1 PVD A 52 2.70 0.41 3.1 0.108
2 PVD B 78 2.86 0.41 15.4 0.117
3 PVD C 52 2.57 (3.91) 0.41 (0.48) 4.6 0.105*
4 PVD D 213 3.98 0.47 21.5 0.230
Notes: The number outside the parentheses is the average value of larger and smaller channels, and the
number in parentheses is for the larger channel only (Figure 2). *Extrapolated value.
Percent passing by weight (%)
100
80
60
40
20
PVDs A and C
PVD B
PVD D
0
0 100 200 300
Apparent opening size (µm)
Figure 9.
Apparent opening size distribution of the PVD filters.
130 GEOSYNTHETICS INTERNATIONAL S 2000, VOL. 7, NO. 2