Kousuke Fujikawa

Effects of inherent anisotropy on deformation and strength characteristics of sands

Hirohumi 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 behaviour, under the present circumstances, 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 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 were simultaneously conducted in the same specimens to examine the influences of inherent anisotropy on strength and elastic shear modulus.
The knowledge obtained by this study is shown as follows:
1) From the results of different sedimentation methods, it was found that orientation of sand particles had close relation with shear strength and shear modulus of the sands.
2) When the angle of the sedimentation direction, which possess particle orientation, becomes large, drained shear strength, qmax, decreases, on the contrary elastic shear modulus, G0, increases.
3) On the samples containing extremely flat particles (mica), although the deformation modulus was very sensitive to the inherent anisotropy, the shear strength was unaffected to the inherent anisotropy. It can be considered that the inherent anisotropy would vanish during shearing because of breakage of mica particles.