A Microstructural Model for Soils and Granular Materials - Multiscale Geomechanics: From Soil to Engineering Projects - page 205

For the numerical simulations, the following parameters had to be determined:
- the parameters of the elastic non-linear law: k n0 , k t0 and n ;
- the parameters of the capillary forces equation: f 0 and S 0 .

k n0 and n were determined from the values of G obtained at dry (or saturated
states). A ratio of k t0 / k n0 = 0.35 was assumed, leading to a Poisson's ratio v = 0.25,
which corresponds to a standard value for this type of material [HIC 96].

The value of N/V was determined by using the chart in Figure 7.4. For a material
with U c >5, a void ratio e = 0.58 corresponded to N/V = 0.31.

S 0 was considered to be equal to ()

r op S in equation [7.21] for d 10 = 0.0024 mm.
f 0 was computed to fit the maximum value of G for the confining pressure of 100
kPa. The material parameters for Glacier Way silt are summarized in Table 7.5.

k n0 n N/V S 0 f 0 (N)

α

2,200 0.35 0.50 0.31 0.175 0.02

Table 7.5. Model parameters for Glacier Way silt

The numerical results are presented in Figure 7.16, together with the
experimental ones [HIC 08]. A good overall agreement was obtained for the two
confining pressures. Starting from the fully saturated state, the shear modulus values
increased slowly, at first, for degrees of saturation varying between 100% and 70%
and then faster up to the maximum values obtained for S r = S 0 . The computed peak
value of G was close to the experimental one for the confining pressure of 50 kPa,
showing a more significant effect of the capillary forces at low confining pressure.
For degrees of saturation below S 0 , the shear modulus values decreased toward the
values obtained for dry states.

Well-documented experimental results on a loose decomposed granitic soil have
been presented by Ng and Chiu [NG 03]. The soil can be described as a silty, clayey,
gravelly sand. Triaxial samples were prepared by the wet tamping method,
compacted with a water content of 19% and dry densities ranging from 74 to 84% of
the Proctor maximum, which corresponded to a void ratio ranging from 0.85 to 1.10
and degrees of saturation ranging from 45 to 58%. Undrained triaxial tests on
saturated samples were performed at different confining pressures and initial void
ratios. They allowed us to determine the model parameters. Table 7.6 summarizes
the set of parameters used for the modeling of the saturated sample behavior.