Environmental Engineering Reference
In-Depth Information
10
−
08
10
−
09
van Genuchten SWCC +
k
a
(
S
w
);
S
r
= 38.9%
Test data from Moldrup et al.
(2003)
Fredlund and Xing SWCC +
k
a
(
S
w
);
S
r
= 38.9%
van Genuchten SWCC +
k
a
(
S
e
);
S
r
= 38.9%
Fredlund and Xing SWCC +
k
a
(
S
e
);
S
r
= 38.9%
10
−
10
10
−
11
10
−
12
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction (kPa)
Figure 9.28
Calculated and measured air coefficient-of-permeability functions for soil tested
by Moldrup et al., (2003).
(e.g.,
<
50 kPa). A zero coefficient of air permeability
should not occur because there is still the diffusion of air
through water. There should be a limiting value of coeffi-
cient of air permeability where the coefficient of air perme-
ability tends toward the diffusion of air through water.
At high soil suction values (e.g., over
ψ
r
), the volumetric
water content should extend to be less than the residual value
(
θ<θ
r
). However, when using the van Genuchten (1980)
SWCC equation, the volumetric water content is asymptotic
to
θ
r
. The volumetric water content must therefore be held
larger than residual water content.
Four air permeability equations were best fit to the
data from Samingan et al. (2003) in order to determine
the coefficients of air permeability
k
a
that were closest
to the dry soil permeability
k
d
in the high-suction range
when using van Genuchten's SWCC equation (Ba-Te et
al., 2005). Different values for residual volumetric water
content were also selected. Figure 9.29 shows that when
the residual water content
θ
r
was 0.035, the combination of
Eqs. 9.82 and 9.84 produced results that were close to the
dry soil permeability. Similar trends were found regarding
the best fit for the air permeability equations applied to the
Moldrup et al. (2003) data, as shown in Fig. 9.30. Setting
the residual water content to zero brings the predicted air
permeability
k
a
closer to the dry air permeability
k
d
for
the combination of Eqs. 9.85 and 9.86. It appears that
10
−
05
10
−
06
10
−
07
10
−
08
10
−
09
van Genuchten SWCC +
k
a
(
S
w
);
S
r
= 6.8%
Test data from Samingan
et al. (2003)
van Genuchten SWCC +
k
a
(
S
w
);
S
r
= 6.8%
van Genuchten SWCC +
k
a
(
S
w
or
S
e
);
S
r
= 0%
10
−
10
10
−
11
10
−
12
10
−
13
10
−
14
10
6
0.1
1
10
100
1000
10,000
100,000
Soil suction (kPa)
Figure 9.29
Calculated and measured air coefficient-of-permeability functions for soil tested
by Samingan et al. (2003) using van Genuchten (1980) SWCC model.
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