Urayama Shohei

Effects of inherent anisotropy on deformation characteristics in mica-mixed sand

Hirofumi Toyota

In order to design and construct the underground structures rationally, it is necessary to conduct seismic response analysis in detail. For that purpose, accurate elastic shear modulus of soils is an important parameter. Moreover, although the real ground has usually anisotropic behavior, the effects of anisotropy on deformation modulus under small strain level have not been deeply understood. An isotropy can be classified as an inherent anisotropy and an induced anisotropy, and the former anisotropy is treated in this study. Specimens are made with changing the angle of sedimentation direction using Toyoura sand and mica. Using those specimens, local small strain (LSS) tests, by which deformation modulus can be measured, and bender element (BE) tests, by which shear wave velocity can be measured, were simultaneously conducted in the same specimens to examine the influences of inherent anisotropy on elastic shear modulus.

The knowledge obtained from this study is shown as follows:

1.The elastic shear modulus increases with increasing angle of the sedimentation direction from the horizontal direction in all mica-mixing rate tested (up to 10%).
2.The influence degree of inherent anisotropy on shear modulus increases with increasing of mica-mixing rate.
3.Toyoura sand shows an elastic shear modulus of approximately constant (linear elastic behavior) up to the level of strain 10-5. However, when mica is mixed into the sand, linear elastic behavior is only shown at the level of smaller strain.
4.Shear wave will propagate faster in mica than Toyoura sand.
5.Although overall mean shear modulus of the specimen is measured in the LSS test, shear wave will propagate in mica selectively in BE test.