Soil-Water Characteristic Curves for Unsaturated Soils - Unsaturated Soil Mechanics in Engineering Practice - page 211

100

Gravimetric water content (experimental data)

80

Volumetric water content (experimental data)

Degree of saturation (experimental data)

60

Void ratio: 0.756
Initial water content: 43.5%
Total density: 2.60 mg/m 3

40

20

0

0 50 100 150 200 250 300 350

Soil suction, kPa

Figure 5.28 Best-fit curves fitted to experimental data of silt soil using three representations of
water content (i.e., degree of saturation, volumetric water content, and gravimetric water content)
(data from Brooks and Corey, 1964).

water content. An upper limit of 10 6 kPa can be built into
Eq. 5.48; however, it should be noted that it is also pos-
sible to use a different maximum value for soil suction.
Equation 5.48 can have a correction factor C(ψ) applied that
can control the shape of the SWCC in the high-soil-suction
range:

where:

ψ r =

soil suction corresponding to the residual water
content θ r .

Equation 5.54 shows that the correction factor C(ψ) is
equal to zero when soil suction is 10 6 kPa. A sample SWCC
plot using Eq. 5.54 is shown in Fig. 5.29. The curve in the
low-suction range is not significantly affected since the cor-
rection function is approximately equal to 1.0 in this region.
Figure 5.30 shows a best-fit curve to the experimental
data obtained for glacial till without using the correction
function C(ψ) (i.e., Eq. 5.48). A best-fit curve to the
same experimental data when using the correction function

θ s

θ(ψ,a f ,n f ,m f ) = C(ψ) (5.53)

(ψ/a f ) n f ]

m f

{ ln[ e + }

The correction factor C(ψ) can be written as follows:

ln ( 1

+ ψ/ψ r )

C(ψ) = −

1 (5.54)

+ ( 10 6 /ψ r ) ]

ln[1

1.0

0.8

a = 10.0
n = 2.0
m = 1.0
ψ r = 3000

0.6

0.4

0.2

0

10 6

0.1 1 10 100 1000 10,000 100,000

Soil suction, kPa

Figure 5.29 Fredlund and Xing (1994) SWCC equation with the correction factor C(ψ) applied
for 10 6 kPa at zero water content.