Small strain stiffness of coarse granular materials measured by wave propagation

Elastic wave velocities transmitted vertically in triaxial specimens of sand, gravel and glass beads were measured by Bender Elements and Trigger-Accelerometers. For the bender element testing, the tested specimens included different size and slenderness, examining effects of specimen shape on the received waveforms. A standard triaxial cylindrical specimen, 5 cm in diameter and 10 cm in height, appeared to be subjected to both near field effects and the reflection of P-waves, which made the determination of S-wave arrival difficult. Effects of wave frequency, reflecting relative wave length compared to grain size, were also investigated. It was found that dynamically obtained stiffness decreased systematically as the relative wave length to grain size increased.