Environmental Engineering Reference
In-Depth Information
Besides the SWCCs, gas diffusivity and void ratio were tab-
ulated (i.e., e
The permeability data from Moldrup et al. (2003)
were presented in terms of the relative air coefficient of
permeability. An arbitrary value of 2
3.0). Results from the test labeled “Miura
4 Andisol” were analyzed by Ba-Te et al., (2005).
The Fredlund and Xing (1994) equation and the van
Genuchten (1980) equation were fit to the experimental
results using a least-squares method. The residual volu-
metric water content was estimated at 29.2 % and the
residual suction was estimated at 1554 kPa for the Moldrup
sample. The SWCC for the Moldrup sample is shown
in Fig. 9.27.
The best-fit soil parameters for both soils are listed in
Table 9.2. The fitting parameters for the SWCC data are
shown for the case where the observed residual conditions
were used as well as the case where the minimum degree
of saturation was set to zero. The coefficients of air per-
meability for the dry soil, k d , are also presented along with
estimated values for the q parameter.
=
10 9 m/s was
assigned for the dry coefficient of air permeability k d .
The generated air permeability equations are plotted
together with the experimental data for the Moldrup soil in
Fig. 9.28. The parameters for the air permeability functions
are shown in Table 9.2. Reasonable agreement was found
over the range of soil suction applied to the soil (i.e.,
50-300 kPa). It appears that leaving the dry permeability
k d as a fixed value in Eq. 9.85 yields a closer fit to the data
than Eq. 9.84, as shown in Fig. 9.28.
×
9.9.4.3 Comparison of Samingan et al., (2003)
and Moldrup et al., (2003) Analysis
The coefficient air permeability equations tend to asymp-
totically approach a zero value when soil suction was low
0.8
van Genuchten SWCC
(1980); S r = 38.9%
Test data from Moldrup et al.
(2003)
Fredlund and Xing SWCC
(1994); S r = 38.9% or 0%
van Genuchten SWCC
(1980); S r = 0%
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
10 6
0.01
0.1
1
10
100
1000
10,000
100,000
Soil suction (kPa)
Figure 9.27 SWCCs best fit to test data from Moldrup et al. (2003).
Table 9.2 Parameters for Fitting Test Data from Moldrup et al., (2003)
θ r ( S res )
(decimal)
Model
a
n
m
ψ r (kPa)
k d (m/s)
q
10 9
Fredlund and Xing
+
k a (S)
2
×
1.126
0.47
0.37
1.26
1554
10 9
0.292
Fredlund and Xing
+
k a (S e )
2
×
1.606
10 9
(0.068)
van Genuchten
+
k a (S)
2
×
1.126
1.19
0.96
0.43
10 9
van Genuchten
+
k a (S e )
2
×
1.604
10 9
Fredlund and Xing
+
k a (S)
2
×
1.126
0.47
0.37
1.26
1544
10 9
Fredlund and Xing
+
k a (S e )
2
×
1.126
0(0)
10 9
van Genuchten
+
k a (S)
2
×
1.132
6.70
3.05
0.04
10 9
van Genuchten
+
k a (S e )
2
×
1.132
 
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