Effects of Initial and Induced Anisotropy on Initial Stiffness of Sand by Triaxial and Bender Elements Tests

Abstract

In this study, to examine the effects of the fabric anisotropy of sand specimen and the anisotropic consolidation stress on the small strain stiffness, the bender elements test and the cyclic and monotonic triaxial tests were performed on several kinds of reconstituted and undisturbed sand samples. These laboratory test results were compared to the results of in-situ seismic surveys. Test results showed that the shear wave velocity estimated from the Young's modulus on triaxial test is lower than those from bender elements and in-situ tests. In particular, it was remarkably recognized in the sample including coarse materials. Therefore, in the case of a comparison of initial stiffness between the laboratory and in-situ tests, the shear wave velocity should be measured in the laboratory test in the same way as the in-situ test.

Anisotropic Stress-Strain Behavior at Small Strains of Clay by Triaxial and Bender Element Tests

“…It can be seen that G hh * is higher than G vh * with an average value of G hh */(G vh * = G hv *) = 1.9. This difference of stiffness between G hh and G vh (G hv ) is much larger than the results from sand specimens (Yamashita et al 2005). It would seem that this is because the difference of clay content and mineralogy of soil.…”

“…The plate was glued to the internal surface of the membrane with buttonholes (rectangular-hole). The BE was glued on a metal plate through a buttonhole on the membrane using quick-drying glue, after the complete preparation of the specimen (Yamashita et al 2005). This method does not disturb the specimen, because the BE does not penetrate into the specimen.…”

Anisotropic small-strain stiffness of calcareous sand affected by sample preparation, particle characteristic and gradation

“…11(a). Based on the conclusion of Yamashita et al (2005) that shear waves propagate faster in the plane parallel to the bedding plane than in the normal one, combined with equation (1), the highest stiffness anisotropy of the air pluviation sample in this study can be explained. Although the pluviation technique is carried out in the water pluviation method, it is deemed that the deposited particles are not aligned horizontally ideally compared with the grains in the air pluviation sample.…”

“…Considering the double peaks of CC and the objectivity, the PP method is finally selected for the signal interpretation. For the signal excitation frequency, Yamashita et al (2005) used the averaged value from the estimated travelling times of 10, 15 and 20 kHz. In this study, it was found that the travel times decrease slightly with an increase in the frequency for the HH and VH waves.…”

Small-strain stiffness of sand subjected to stress anisotropy

“…On the other hand, Rampello et al [17] reported notably higher values of G max for reconstituted clayey samples compressed anisotropically compared to those compressed isotropically at the same mean effective stress (p′). Using the results of tests performed in the true triaxial apparatus equipped with bender elements, it has also been shown that the small-strain shear modulus of sands is mainly influenced by the principal stresses in the direction of wave propagation and particle motion and is nearly independent of the out of plane stress component ( [1,5,13,15,18,19,24,26,27,28]). Accordingly, the small-strain shear modulus model, Eq.…”