Environmental Engineering Reference
In-Depth Information
Table 4.13 Equilibration Times When Using Filter
Paper Method
....
1,000,000
Drying
Wetting
100,000
Equilibrium
Filter Paper
10,000
References
Time
Method
1,000
Fawcett and
Collis-George
(1967)
6-7 days
Contact
100
10
McQueen and
Miller (1968a)
7 days
Contact
1
Al-Khafaf and
Hanks (1974)
2 days
Contact and
uncertain
contact
0
10
20
30
40
50
60
Filter paper water content, %
(a)
1,000,000
Hamblin (1981)
Minutes-
36 days
Contact
Drying
Wetting
100,000
Chandler and
Gutierrez (1986)
5 days
Contact
10,000
Duran (1986)
7 days
No contact
Greacen et al.,
(1987)
7 days
Contact
1,000
Sibley and Williams
(1990)
3 days
10 days
Contact
Noncontact
100
Lee and Wray
(1992)
14 days
Contact and no
contact
10
Houston et al.,
(1994)
7 days
Contact and no
contact
1
0
10
20
30
40
50
60
Filter paper water content, %
Harisson and Blight
(1998)
7-10 days
Wetting and no
contact
Drying and no
contact
Wetting and no
contact
Drying and no
contact
(b)
Figure 4.81
Wetting and drying responses of filter paper over
different concentrations of salt solutions in desiccators at 24
o
C
(from Rahardjo and Leong, 2006): (a) calibration for Whatman
No. 42 filter paper; (b) calibration for Schleicher and Schuell No.
589 filter paper.
21 days
10 days
25-30 days
Filter papers absorb water from the soil specimen when
the wetting method is used to measure soil suction. The soil
specimen becomes slightly drier and exhibits a higher suc-
tion. Figures 4.82a and 4.82b show the equilibration times
for Whatman No. 42 and Schleicher and Schuell No. 589
filter papers, respectively. The wetting method was used in
conjunction with (i) a pressure plate apparatus, (ii) equilibra-
tion over salt solutions, and (iii) equilibration over distilled
water. Equilibration times when using a 500-mL container
were between 2 and 5 days. The longest equilibration time
was 14 days which was required for filter paper placed over
distilled water (Fig. 4.82).
filter papers over salt solutions of various concentrations
in vacuum desiccators. Matric suction data for initially dry
filter papers were obtained using the pressure plate appara-
tus. The calibration data are shown in Fig. 4.83. The results
indicate that the filter paper responses are different for total
and matric suctions calibration curves. This behavior was
also observed by Houston et al., (1994) and Harrison and
Blight (1998).
The suction data indicate that for suctions less than
1000 kPa the water content of the filter paper has a lower
and different response to total suction than to matric suction.
Above 1000 kPa, the total and matric suction calibration
curves appear to converge. Houston et al. (1994) found that
filter paper buried in a soil had essentially the same water
content as filter papers suspended above the soil for suction
values of about 98,100 kPa. Fredlund (1992) and Al-Khafaf
4.3.3.4 Total Suction and Matric Suction Calibration
Curves
Leong et al. (2002a) and Rahardjo and Leong (2006) devel-
oped total and matric suction calibration curves for What-
man No. 42 and Schleicher and Schuell No. 589 filter paper.
Total suction data were obtained by calibrating initially dry
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