A Microstructural Model for Soils and Granular Materials - Multiscale Geomechanics: From Soil to Engineering Projects - page 207

A stabilization of the volume change was observed at large deformations. This
contractive behavior led to an increase in the degree of saturation for all samples,
since the water content was kept constant. The initial degree of saturation was equal
to 43% for the three specimens and the final degree of saturation reached 48 to 61%,
according to the amount of volume change during the tests. Measured suctions
showed a decrease of 8 to 15 kPa for the most contractive specimen (Figure 7.18).
Figure 7.18. Evolution of suction during triaxial tests at constant water content
For numerical simulations, determining the material parameters S 0 and f 0 was the
necessary first step [HIC 07]. S 0 was determined by using equation [7.21],
considering that the mode of preparation by compaction was similar to the one used
by Wu et al. [WU 84]. f 0 was determined from the test result at the confining stress
of 100 kPa in order to obtain a computed strength identical to the experimental one.
From this analysis, we retained that S 0 = 0.2 and f 0 = 0.01 N. The other parameters
were kept identical to those used in the modeling of the saturated samples. The
results of the numerical simulations are presented together with the experimental
ones in Figure 7.17. The stress−strain relationship shows a good agreement between
experimental and numerical results for the three confining pressures. In particular,
the values of the maximum strength at large deformations are computed with good
accuracy. The computed volume changes also correspond to a contractive behavior
of the three specimens. The comparison with experimental results shows that the
amplitudes of volume change given by the model are less dependent on the
confining pressure than those measured, but experimental and numerical results
remain reasonably close.