Anisotropic Dynamic Loading Effects on Unsaturated Sand Shear Modulus Prepared at Different Compaction Water Contents

Dynamic properties of soil, such as shear modulus and damping ratio, are necessary for analyzing the dynamic response of the soil in geostructures. This study investigates the effects of partially inherent anisotropy and stress-induced anisotropy on the shear stiffness of unsaturated soil through a series of dynamic hollow cylinder tests at medium strain levels. The different inherent anisotropy in tested sand specimens was introduced through different compaction water contents in the sample preparation stage while keeping the void ratio nearly constant. Moreover, the influences of the angle of maximum principal stress, α, and intermediate principal stress parameter, b = (σ₂ − σ₃)/(σ₁ − σ₃), as stress-induced anisotropy parameters are examined at the dynamic loading stage. The experimental results suggested that the b-parameter has no noticeable influence on shear modulus. On the contrary, shear modulus values showed a peak by changing the value of α from 15° to 75°, with symmetric trends with respect to α = 45°. The impact of compaction water content on the stiffness-α trend was negligible, whereas it affected the stiffness-b to some extent.