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7.3. Results of numerical simulation on Hostun sand
7.3.1.
Drained triaxial tests
A series of drained triaxial tests on coarse Hostun sand performed by Bouvard
[BOU 82] were reported and analyzed by Biarez and Hicher [BIA 94]. The tests
were performed at different confining pressures on samples prepared at different
initial void ratios. Typical results are presented in Figure 7.3, which shows the
triaxial testing results for both dense and loose specimens made of Hostun sand. The
stress−strain curves are plotted for three different confining stresses in Figure 7.3a.
The void ratio change with respect to strain is plotted in Figure 7.3b.
3
0.8
Loose
Dense
Loose
Dense
0.1MPa
0.7
0.3MPa
0.8 MPa
2
0.8MPa
0.3MPa
0.6
0.1MPa
0.8MPa
0.3 MPa
1
0.5
0.1 MPa
0.4
0
0
5
10
15
20
0
5
10
15
20
ε
1
(%)
ε
1
(%)
Figure 7.3.
Drained triaxial tests on Hostun sand [BOU 92]
We can see the combined influence of the initial void ratio and the mean
effective stress on the stress−strain curves and the volumetric change. The
stress−strain curve presents a peak corresponding to the dilatancy of the sample,
which increases with its initial relative density. For dilative materials, the deviatoric
stress reduces after the peak and moves towards a constant state of stress for a
constant void ratio corresponding to the critical state. In practice, it is difficult to
reach this state because of strain localization, especially in dense materials. It is
possible, however, to limit the effect of the localization by reducing the thickness of
the specimen and taking measures to minimize the friction between the rigid end
plates and the specimen. This was done in the tests presented here, which allowed
the strain localization to be delayed at large deformations. The critical state could,
therefore, be determined with sufficient accuracy [BIA 94]. If this were not the case,
Biarez showed that the position of the critical state line could be obtained by using
the following correlations:
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