Name: Yukihiro Yonekawa

Thesis title: Research on deformation and strength anisotropy of mica mixture sands

Supervisor: 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 behavior, 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 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 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.Toyoura sand shows an elastic shear modulus of approximately constant (linear elastic behavior) up to the level of strain 10-5. However, mica is mixed into the@sand, linear elastic behavior is shown at the level of smaller strain.
2.All mica mixing ratio, the elastic shear modulus increases with increasing angle of the sedimentation direction from the horizontal direction.
3.Enough to contain many flat soil particles, the elastic shear modulus of small strain region is greatly affected by the inherent anisotropy. In other words, in small strain region, a large flat nature of the mica affects the inherent anisotropy.
4.In the samples containing mica, the drained 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.
5.When the angle of the sedimentation direction, which possesses particle orientation, becomes large, drained shear strength decreases, on the contrary elastic shear modulus increases.