Environmental Engineering Reference
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Figure 8.9 Subdivision of SWCC for calculation of water coefficient of permeability from
SWCC (after Marshall, 1958; Kunze et al., 1968).
6
5
4
Measured k w (from Gonzales
and Adams, 1980)
Computed k w
Drying curve
3
2
1
0
0
10
15
20
25
30
35
40
45
5
Matric suction ( u a - u w ), kPa
Figure 8.10 Comparisons between the computed and measured coefficients of permeability
(after Gonzalez and Adams, 1980).
permeability models based on the physical model suggested
by Childs and Collis-George are the Burdine (1953) and
Mualem (1976a) permeability models. The saturated coeffi-
cient of permeability and the SWCCs are used to solve the
integral form of the statistical models and thereby compute
a water permeability function.
Statistical models can be used to calculate the permeability
function when the saturated coefficient of permeability k s
and the SWCC are known. This approach assumes that the
permeability function and the SWCC are both closely related
to the pore-size distribution of the soil. Figure 8.12 shows
a typical SWCC for a silt soil along with its permeability
function. Burdine (1953) proposed the following equation
for the relative coefficient of permeability based on pore-size
distribution:
θ r
θ
dθ/ [ ψ 2 (θ) ]
k s n
k w (θ)
=
(8.11)
θ r
θ s
dθ/ [ ψ 2 (θ) ]
 
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