Assessment of Conventional Interpretation Methods of RC Results Based on 3D Numerical Simulations

Abstract

Resonant column (RC) testing is a widely used laboratory technique to determine the stiffness characteristics of soils under small- to medium-strain perturbations. Solid or hollow cylindrical soil specimens are set into motion in either torsional or longitudinal modes of vibration by an electromagnetic loading system whose frequency is changing until the first-mode resonant condition is reached, and then the shear modulus of soil is back-calculated from the fundamental frequency, the geometry of the specimen, and the end-restraint conditions. However, the outcomes of this test are largely affected by both the driving apparatus used for the specimen vibration and the motion-monitoring instruments lumped into a mass that oscillates with the specimen. This study presents the results pertaining to three-dimensional (3D) finite-differences (FD) simulations of RC tests on soil samples undergoing both torsional and longitudinal modes of vibration. The prime objective of the study was to examine the influence of the driving mass, the geometry of the specimen, the mode of vibration, and the boundary conditions on the RC test results. The numerical results show that the attachment of the instrumentation on the sample is the driving factor contributing to the error in the estimation of the soil dynamic characteristics, and typical equations for the calculation of the shear modulus from the resonant frequency in the longitudinal mode of vibration cannot be directly applied to their torsional-mode counterparts.