Measurement and Estimation of State Variables - Unsaturated Soil Mechanics in Engineering Practice - page 159

Table 4.12 Suction Control Procedure for Filter Paper Calibration

Suction Generation Method Suction Range References

Suction plate, pressure membrane
extractor, pressure plate

0-1500 kPa Fawcett and Collis-George (1967)

McQueen and Miller (1968a)
Al-Khafaf and Hanks (1974)
McKeen (1980)
Hamblin (1981)
Greacen et al. (1987)
Sibley and Williams (1990)
Sibley et al. (1990)
Houston et al. (1994)
Harrison and Blight (1998)

Salt solutions 0-340,000 kPa Gardner (1937)

Fawcett and Collis-George (1967)
McQueen and Miller (1968a)
Al-Khafaf and Hanks (1974)
McKeen (1980)
Hamblin (1981)
Chandler and Gutierrez (1986)
El-Ehwany and Houston (1990)
Sibley and Williams (1990)
Sibley et al. (1990)
Houston et al. (1994)
Harrison and Blight (1998)

Field soil samples 0-2000 kPa McQueen and Miller (1968a)

Al-Khafaf and Hanks (1974)

Oedometer and triaxial samples 100-2000 kPa Gutierrez (1985)

Duran (1986)
Chandler and Gutierrez (1986)
Chandler et al. (1992)

Centrifuge 100-3100 kPa Gardner (1937)

was observed. Houston et al. (1994) reported no measurable
differences between the wetting and drying calibration curves
for matric suctions between 8 and 2500 kPa. Leong et al.
(2002a) conducted drying and wetting calibrations of the
Whatman No. 42 and Schleicher and Schuell No. 589 fil-
ter papers. Wetting and drying calibration data from Leong
et al., (2002a) along with other data from the research litera-
ture are plotted in Figs. 4.79a and 4.79b for Whatman No. 42
and Schleicher and Schuell No. 589 filter paper, respectively.
The data were obtained by either suspending the filter paper
above salt solutions (i.e., no contact) or placing the filter paper
on a suction plate, a pressure plate, or a pressure membrane
apparatus (i.e., contact).
No-contact hysteresis (i.e., total suction) of Whatman No.
42 and Schleicher and Schuell No. 589 filter papers on
drying and wetting was investigated using three methods:
(i) distilled water in a vacuum desiccator (i.e., suction of
0 kPa), (ii) salt solution in a vacuum desiccator (i.e., total

suction equal to 9700 kPa), and (iii) air environment with a
relative humidity of 60% (i.e., total suction equal to 70,000
kPa). The changes in the water content of the filter paper,
w f , with time under the three conditions are shown in Figs.
4.80a and 4.80b for Whatman No. 42 and Schleicher and
Shuell No. 589, respectively. Hysteresis can be observed in
the filter paper responses. Both types of filter paper show
12% differences in water content for distilled water equi-
libration; 1% differences in water content for salt solution
equilibration; and 0.5% differences in water content for the
air environment equilibration. The equilibration times when
using the drying mode were longer than the equilibration
times required when using the wetting mode. The equili-
bration time was about 28 days for drying and 14 days for
wetting when using the distilled water method. The results
showed that inadequate equilibration times can produce the
appearance of significant hysteresis between the wetting and
drying equilibrium conditions for the filter paper.