1506
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
Figure 6. Strains Changes variation through the first and fifteenth cycle
Figure 7.Shear modulus ratio changes with shear strain
Figure 8. Damping ratio changes with shear strain
In all tests the direction of the major principal stress and
intermediate principal stress varies for various tests, but kept
constant during each specific test. The response of samples has
been investigated under constant loading direction and deviator
stress. Results showed that stress anisotropy has significant
effect on soil response and the excess pore water presure
generation. At triaxial compression (α=10
o
) and triaxial
extension (α=80
o
) tests the specimens resist over excess pore
water pressure build up.
Test results show that the sand anisotropic behavior will be
magnified by changing the principal stress direction. In a test
under a constant condition of α, b and loading magnitude, the
shear strength could be higher in a direction than in its opposite
direction. This difference in directional strength of the sand is
maximum in some loading directions (α=10
o
and 80
o
) and
minimum in α=45
o
. These differences are result of the direction
dependent interlock of the sand particles and come from the
sedimentary condition.
By changing α, the loading condition of the specimens will
be changed. These changes in loading condition by affecting on
the specimens strain pattern would cause different responses. As
for the α=10
o
and 80
o
tests, the main part of the specimens
deformation result from axial or radial strains and the shear
strain is the major part of strain in specimen tested at α=45
o
.
This type of stress anisotropy had not significant effect on
shear modulus and damping ratio of the specimens.
This kind of anisotropy come from the induced stress status
(induced anisotropy) and will be magnified by the directional
dependent properties of sand interlocks (inherent anisotropy).
So the separation of inherent and induced anisotropy effects
may have not been simply possible.
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