Air Flow through Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 476

0.8

Test data from Samingan et al., (2003)
Best-fit SACC for data from Samingan et al. (2003)
Test data from Moldrup et al., (2003)
Best-fit SACC for data from Moldrup et al. (2003)

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 9.25 SACCs best fit with Fredlund and Xing (1994) SWCC equation for test data from
Samingan et al., (2003) and Moldrup et al., (2003).

above equations. In total, four air permeability functions
were computed. The variable q can be determined using a
least-squares technique for each of the four equations. The
coefficient of air permeability under dry conditions was not
independently measured for the soil tested by Samingan
et al., (2003). Therefore, the dry soil coefficient of air
permeability was considered as an independent variable and
obtained using a least-squares method. The air permeability
functions were then computed.
The estimated air permeability results were plotted
together with the experimental data for the Samingan soil in

Fig. 9.26. The parameters for the air permeability functions
are shown in Table 9.1. Reasonable agreement between the
measured and estimated air coefficient of permeability was
found in the range over which the tests were performed
(i.e., 50 - 300 kPa).

9.9.4.2 Moldrup et al. (2003) Results
Moldrup et al. (2003) presented data on SWCCs and gas
diffusion coefficients as a function of water content for 22
soils from Japan. The measurements were originally con-
ducted to evaluate factors that influence plant performance.

10 − 04

10 − 05

10 − 06

10 − 07

10 − 08

van Genuchten SWCC +
k a ( S w ); S r = 6.8%
Test data from Samingan
et al. (2003)
Fredlund and Xing SWCC +
k a ( S w ); S r = 6.8%
van Genuchten SWCC +
k a ( S e ); S r = 6.8%
Fredlund and Xing SWCC +
k a ( S e ); S r = 6.8%

10 − 09

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 9.26 Calculated and measured air coefficient of permeability functions for soil tested
by Samingan et al., (2003).