Hydro-Mechanical Properties of an Unsaturated Frictional Material

42 CHAPTER 2. STATE OF THE ART
Volumetric water content (-)
Volumetric water content (-)
50
40
30
20
10
0
50
40
30
20
10
0
Volumetric water content (-)
50
40
30
20
10
results Brooks and Corey (1964) Van Genuchten (1980) a, n, m=1/(1-n) Experimental
0
Best fit Air-entry value
Residual suction zone Residual
(1980) Genuchten Van 0 1 10
Suction (kPa)
100
50
0 1 10
Suction (kPa)
100
40
Volumetric water content (-)
0 1 10 100
Suction (kPa)
30
20
10
0
a, n, m Fredlund and Xing (1994)
0 1 10 100
Suction (kPa)
Figure 2.15: Experimental results for Hostun sand from drainage: soil-water characteristic
curve and fitted results using empirical models
(see Chapter 6) are fitted using the above mentioned equations. In general good agreement
between observed and calculated values was found for all used models. An disadvantage of
the equation proposed by Brooks and Corey is, that the calculated results in the region of
the air-entry value are not proper conform to the experimental results. The calculated results
fit well to the experimental results in the saturated zone, transition zone and residual zone.
Comparing the experimental and calculated results using van Genuchten’s equations it can be
observed that the calculated results in the region of the residual suction as well as the residual
zone are in better agreement to the experimental results when using the flexible parameter
m. Good fit was found when using Fredlund and Xing’s equation. Whereas van Genuchten’s
equation does not tend to 0 in the residual zone, Fredlund and Xing’s equation even considers
the water content to be 0 at a suction of 10 6 kPa.
The influence of the parameters α and λ on the shape of the curve is given in Fig. 2.16
for Brooks and Corey’s equation. The parameter α is changing while the parameter λ is kept
constant in Fig. 2.16 on the left hand side. With decreasing α the curve is shifting to larger
values of suction and the air-entry value is increasing. When λ is decreasing the slope of the
curve is decreasing.