A Microstructural Model for Soils and Granular Materials - Multiscale Geomechanics: From Soil to Engineering Projects - page 204

The first example concerns the results obtained by Wu et al . [WU 84] on a silty
material called Glacier Way silt compacted in dry condition in a mould and then
saturated. The samples are then dried to various degrees of saturation for the
different specimens tested in the resonant column in order to obtain their elastic
properties as a function of the degree of saturation. Figure 7.16 presents the results
obtained for the Glacier Way silt for two different confining pressures. The value of
G was the same for S r = 0% and S r = 100%. A well-marked peak for the two
confining pressures could be observed, which occurred for a value of S r around 17%.
The maximum value of G was 1.8 times its value for dry and saturated states, at a
confining pressure of 50 kPa and 1.6 times at a confining pressure of 100 kPa. The
capillary effect appeared to be more pronounced at lower confining pressures.

Figure 7.16. Shear modulus function of the degree of saturation for Glacier Way silt

The general trend showing the evolution of the shear modulus with the degree of
saturation is in agreement with the model's concepts. This implies an identical value
of G at dry and fully saturated states in the absence of capillary forces and a
maximum influence of these forces at an optimum degree of saturation, as given by
equation [7.20], in which S 0 corresponds to ()
r

S

in equation [7.21].

opt

To determine the capillary forces, equation [7.19] includes two material
parameters, c and d . Very little information could be gathered on these two
parameters by simply using the test results. We therefore decided to take a constant
value c = 8 and a value d function of the mean grain size d 50 : d = 1.1 d 50 . These
values gave a standard evolution for the capillary forces, function of the distance
between particles, as well as an initial isotropic distribution of these forces.