Novel evaluation of mass polar moment of inertia of the drive plate in resonant column

Abstract

Resonant column (RC) is a standard laboratory test for the dynamic characterization of soils. Mass polar moment of inertia (MPMI) of the drive plate of RC is required for the solution of equation of motion for a specimen-mass system in RC. In standard procedure, the MPMI is evaluated by testing of calibration probes. Studies have shown that torsional stiffness of the probes have significant effect on the evaluation of MPMI of drive plate due to contribution from base of RC. The extent of contribution increases with increase in torsional stiffness of probes and consequently error in MPMI increases. This study presents a new calibration method that does not use probes. The MPMI of the drive plate is evaluated by suspension of drive plate with polyamide wire of negligible torsional stiffness and damping. The modified equation of motion is used to evaluate the MPMI of drive plate. Results show that the variation of MPMI with frequency is very small compared to its variation from conventional procedure. The apparent values of MPMI from conventional procedure are found to be higher than its inferred true-value, which results in overestimation of shear wave velocity of soil specimen.