Characterization of soil stiffness anisotropy at small strains based on phase velocities of shear waves measured by novel testing apparatus

¹ Department of Civil Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8654, Japan
² Public Works Research Institute, 1-6 Minamihara, Tsukub, Ibaraki-ken, 305-8516, Japan
³ Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan

^* Corresponding author: j-liu@iis.u-tokyo.ac.jp

Abstract

For the characterization of soil stiffness anisotropy at small strains and the calculation of soil elastic constants derived from the cross-anisotropic model, it is important to obtain stress wave phase velocities of soils in both principal and oblique directions. This study developed an original eight-prismatic shape apparatus equipped with disk-shaped shear plates to measure shear (S-) wave phase velocities (V_phase) in multiple directions, and four granular materials of various shapes were tested by this apparatus under isotropic confinement. Experimental results confirm the capability of the new apparatus and reveal that both S-wave propagation and oscillation directions are sensitive to soil inner fabric, i.e., V_s changes with the variation of either S-wave propagation or oscillation direction. Based on the experimental observations, it is suggested to keep the same S-wave oscillation direction when measuring V_s in multiple propagation directions so that the corresponding shape of the S-wave surface (polar plots of V_s in arbitrary propagation directions) is more precise to reflect the small-strain stiffness anisotropy of soils.