Hydro-Mechanical Properties of an Unsaturated Frictional Material

2.5. CONSTITUTIVE MODELS FOR HYDRAULIC FUNCTIONS 47
developed do not consider hysteresis the models by Zou (2003, 2004), Rojas & Rojas (2005)
take hysteresis into account.
Following are physical models that have been adopted in the present investigation. The
models by Aubertin et al. (2003) and Zou (2003, 2004) were chosen to predict the soil-water
characteristic curve of Hostun sand.
- Kovacs (1981), Aubertin (2003)
Kovacs (1981) proposed a model, that was extended by Aubertin et al. (2003) for a
general application to porous media. The model makes use of a reference parameter
defined as the equivalent capillary rise of water in a porous medium to define the rela-
tionship between saturation and matric suction. The equivalent capillary rise is derived
from the expression for the rise of water in a capillarity with certain diameter. Two
components of saturation are considered: i) the saturation held by capillary forces, the
component that is obtained from cumulative pore-size distribution function and ii) the
saturation held by adhesive forces at higher suction values, that is the van der Waals
attraction between grain surface and water dipoles. Following Aubertin et al. (2003),
where the coefficient of uniformity Cu, the diameter corresponding to 10% passing the
grain-size distribution curve D10, the void ratio e and a shape factor α are used, the
drainage suction-saturation relationship was preliminary estimated for loose as well as
dense Hostun sand specimens as given in Fig. 2.21. Estimated results are compared to
experimental results carried out for Hostun sand specimens (see Chapter 6). Parameters
used for the prediction are given in Tab. 2.3. The soil classification parameter D10 is
estimated from the grain-size distribution curve (see Fig. 5.1) and Cu is calculated using
the following relation:
Cu = D60
D10
(2.16)
where: D60 and D10 are the diameters corresponding to 10% as well as 60% passing the
grain-size distribution curve. According to loose and dense packed specimen the void
ratio is taken. The shape factor α is chosen following Kovacs (1981), who suggested
α = 10.
- Zou (2003, 2004)
Table 2.3: Parameters used for prediction of soil-water characteristic curve (Aubertin et al.
(2003)
D10 Cu e α
Loose specimen 0.21 1.72 0.89 10
Dense specimen 0.21 1.72 0.66 10