Environmental Engineering Reference
In-Depth Information
35
Experimental
n
p
= 0.4
n
p
= 0.53
n
p
= 0.7
30
25
20
15
10
5
0
10
6
0.01
0.1
1
10
100
1000
10,000
100,000
Soil suction, kPa
Figure 5.108
Effect of varying packing factor
n
p
for sand (data from Mualem, 1984).
30
Experimental
n
p
= 0.36
n
p
= 0.40
n
p
= 0.435
n
p
= 0.50
25
20
15
10
5
0
0.01
0.1
1
10
100
1000
10,000
100,000
10
6
Soil suction, kPa
Figure 5.109
Effect of varying packing factor
n
p
for silt (data from Schuh et al., 1991).
showed that the
α
value varied among textural classes and
ranged from 1.1 for fine-textured soils to 2.5 for coarse-
textured soils. The
α
value was estimated in accordance
with the values shown in Table 5.10. The Arya and Paris
(1981) method requires a well-defined grain-size distribution
curve. Several estimations performed using the Arya and
Paris (1981) pedo-transfer function are shown in Fig. 5.110.
Scheinost et al., (1997).
The Scheinost et al., (1997)
pedo-transfer function uses a linear regression analysis to esti-
mate the parameters for a vanGenuchten (1980) equation. The
Scheinost pedo-transfer functionwas developed to account for
extreme variations in the soil parameters, with textures vary-
ing from gravels to clays, organic contents over a wide range,
and bulk densities from 0.80 to 1.85 mg/m
3
. The parameters
for the pedo-transfer function were obtained using a soil data
set from Germany. The Scheinost et al. (1997) pedo-transfer
function was able to estimate the desaturation rate of most
soils with reasonable accuracy.
Rawls and Brakensiek (1985).
The Rawls and Brak-
ensiek (1985) pedo-transfer function is based on a regres-
sion analysis that estimates parameters for the Brooks and
Corey (1964) equation. While the estimation of the air-entry
value for most soils seems reasonable, the desaturation rate
appears to generally be overestimated.
Vereecken et al., (1989).
The Vereecken et al. (1989)
pedo-transfer function uses a statistical regression analysis
to estimate the parameters for the van Genuchten (1980)
equation. The Vereecken et al. (1989) pedo-transfer func-
tion has been applied to a wide range of soils and has
the ability to account for high-organic-matter contents. In
Search WWH ::
Custom Search