Hydro-Mechanical Properties of an Unsaturated Frictional Material

2.5. CONSTITUTIVE MODELS FOR HYDRAULIC FUNCTIONS 43
Volumetric water content (-)
50
40
30
20
10
0
Volumetric water content (-)
alpha = 0.3
0 1 10 100
Suction (kPa)
= 0.7 alpha = 0.5 alpha
50
40
30
20
10
0
0 1 10 100
Suction (kPa)
= 2.5 lambda = 1.5 lambda = 0.5 lambda
Figure 2.16: Influence of Brooks and Corey parameters α and λ on the shape of the soil-water
characteristic curve
Volumetric water content (-)
50
40
30
20
10
0
= 0.55 alpha = 0.35 alpha = 0.15 alpha
0 1 10 100
Suction (kPa)
50
40
30
20
10
0
0 1 10 100
Suction (kPa)
= 6.0 n = 4.0 n = 2.0 n
Genuchten (1980)
Figure 2.17: Influence of van Genuchten parameters α and n on the shape of the soil-water
characteristic curve (in case m is a function of n)
Van
The influence of the parameters α and n on the shape of the curve is presented in Fig. 2.17
using van Genuchten’s equation. In this case the parameter m is fixed to m = 1−1/n. Similar
to Brooks and Corey with decreasing α the curve is moving to larger values of suction. A
change of α influences the air-entry value. When n is changing while α is kept constant
the curve is rotating around its inflection point. With decreasing n the transition zone is
increasing and the value of the residual suction is also increasing. The slope of the curve
becomes lower when the parameter m is decreasing as shown in Fig. 2.18. Here m is a flexible
parameter.
The influence of the parameters α, n and m on the shape of the curve for Fredlund and
Xing’s equation shows Fig. 2.19. An increase in the parameter α causes a shift of the curve to