Hydro-Mechanical Properties of an Unsaturated Frictional Material

48 CHAPTER 2. STATE OF THE ART
Saturation (-)
1.0
0.8
0.6
0.4
0.2
0.0
0.1 1 10
specimen Experimental results dense specimen Experimental results loose specimen
100
Suction (kPa)
dense specimen Prediction loose Prediction
Figure 2.21: Estimated drainage soil-water characteristic curve for Hostun sand using the
model by Aubertin et al. (2003) in comparison with experimental results (loose and dense
specimen)
To predict the boundary hysteresis curves and the scanning curves of unsaturated soils
a physical model was proposed by Zou (2003, 2004) and tested on Hostun sand (Lins
et al. 2007). Because the equations are not trivial it is explained in more detail in
Appendix A. In this model, pores in an unsaturated soil are considered to be composed
of the contact regions between two tangent soil particles and the irregular frustum-
shaped pores among several adjacent particles (Fig. 2.22 a)). It is also assumed that
all particles in the soil are sphere-shaped and have the same sphere radius rs and that
all frustum-shaped pores are regular symmetrical frustum-shaped pores which have the
same height rs, the same lower radius r1 and the same upper radius r1 + ξ · rs (Fig. 2.22
b)). The average number of the contact points of a particle with its neighbors is termed
as contact number nc. The average number of the frustum-shaped pores per particle is
called as frustum number nf0.
The model includes 7 parameters. To determine the influence of the parameters on the
shape of the curves an analysis was performed. While the influence of the parameter
nc is negligible the parameters αmax, nf0, ξ, ζ, µ and Sr0 are influencing the shape of
the soil-water characteristic curve. To clarify the influence of the parameters on the
shape of the soil-water characteristic curve, it is classified into three sections, namely
the saturated zone, the unsaturated zone as well as the residual zone. Additionally
typical parameters for the air-entry value ψaev, the saturated volumetric water content
θs, and the residual volumetric water content θr, with the corresponding residual suction
ψr, and the water-entry value ψwev are used (see also Fig 2.8). The parameter ξ is