Development of vertical and horizontal disk transducers for wave velocity measurements in a large rectangular specimen

Institute of Industrial Science, The University of Tokyo, Japan

^* Corresponding author: t-dutta@iis.u-tokyo.ac.jp

Abstract

For the accurate design of structures subjected to both static and dynamic loadings, elastic wave velocity and small strain stiffness are essential parameters. Numerous techniques have been developed to estimate wave velocities of geomaterials. Bender elements which are widely adopted for wave velocity measurements are invasive in nature and are not suitable for coarse-grained materials. In the present study, new design configuration of disk transducer has been introduced to measure both vertical and horizontal wave velocities for coarse granular soils considering multidirectional oscillation of propagating waves. An innovative arrangement of both compression and shear type elements has been installed in a large-sized triaxial apparatus having rectangular specimens of size 236×236×500 mm to assess the wave velocities. The materials described are Toyoura sand (D₅₀ = 0.24 mm) and Oiso gravel (D₅₀ = 11.8 mm). This arrangement enables measurements of nine types of wave velocities, and thus the stiffness anisotropy to be quantified. For Oiso gravel, horizontal wave velocities are greater than vertical wave velocities for both shear and compression waves. For Toyoura sand, shear wave velocities are higher in horizontal direction of propagation, whereas similar compression wave velocities are observed from both horizontal and vertical directions.