Environmental Engineering Reference
In-Depth Information
80
1,000,000
Pressure plate - 20 kPa
Pressure plae - 40 kPa
Pressure plate - 60 kPa
Pressure plate - 100 kPa
Pressure plate - 1000 kPa
Pressure plate - 1500 kPa
Salt solution - 910 kPa
Salt solution - 1810 kPa
Salt solution - 3190 kPa
Salt solution - 9700 kPa
Distilled water - 0 kPa
Matric suction test data
Equations 4.15 & 4.16
Total suction test data
Equations 4.17 & 4.18
70
100,000
60
10,000
50
1,000
40
Matric suction
30
100
20
Total suction
10
10
1
0 2 4 6 8 101214161820222426
Duration, days
0
20
40
60
80
100
Filter paper water content, %
(a)
(a)
80
Pressure plate - 1000 kPa
Pressure plate - 1500 kPa
Salt solution - 910 kPa
Salt solution - 1810 kPa
Salt solution - 3190 kPa
Salt solution - 9700 kPa
Distilled water - 0 kPa
1,000,000
Matric suction test data
Equations 4.19 & 4.20
Total suction test data
Equations 4.21 & 4.22
70
100,000
60
50
10,000
40
1,000
30
Matric suction
100
20
Total suction
10
10
0 2 4 6 8 101214161820222426
Duration, days
1
0
20
40
60
80
100
Filter paper water content, %
(b)
(b)
Figure 4.82 Equilibration of filter papers placed in pressure plate
apparatus over salt solution or distilled water (from Rahardjo and
Leong, 2006): (a) response of Whatman No. 42 filter paper; (b)
response of Schleicher and Schuell No. 589 filter paper.
Figure 4.83 Proposed total and matric suction calibration curves
(from Rahardjo and Leong, 2006): (a) calibration of Whatman No.
42 filter paper; (b) calibration of Schleicher and Schuell No. 589
filter paper.
and Hanks (1974) also reported that matric suction curves
were essentially the same as total suction curves in the
high-suction range.
Field measurements of soil suction using filter paper by
van der Raadt et al. (1987) showed that filter paper placed
in contact and no contact were similar for suctions greater
than 1000 kPa. It was suggested that at suctions greater
than 1000 kPa most moisture movement occurred through
vapor transfer rather than capillary transfer. It was suggested
that the contact filter paper method can be used to reliably
measure matric suction as long as the suctions were less
than 1000 kPa. It was suggested that the no-contact method
would tend to measure total suctions when the suction values
were greater than 1000 kPa.
Calibration Equations. A number of equations have
been suggested for Whatman No. 42 and Schleicher and
Schuell No. 589 filter paper calibration curves over the
years (Table 4.10). Hamblin (1981) suggested that the
calibration equation obtained by other researchers can be
used for Whatman No. 42 filter paper unless particular
accuracy demands recalibration. The filter paper method is
particularly attractive for the measurement of soil suction
when the calibration of the filter paper can be avoided. The
calibration results presented in Fig. 4.76 indicate that the
performance of the Whatman No. 42 filter paper may be
slightly more consistent than the Schleicher and Shuell No.
589 filter paper.
The overall calibration curve is usually represented by
two equations that represent different sensitivity of the filter
paper response in the higher and lower suction range. All the
equations presented in Table 4.10, except that of Hamblin
(1981), are of the form
log ψ = a b w f
(4.14)
where:
log ψ =
logarithm of suction (kPa) to base 10,
a, b
=
fitting constants for the calibration curve, and
w f
=
filter paper water content, %.
 
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