A modified linear-elastic model for calibration of resonant column devices accommodating drive system compliance

Abstract

Measurements of small-strain shear modulus of soils and rocks using the resonant column apparatus are highly dependent on accurate physical characterisation of the apparatus's drive components. This is typically achieved via a calibration exercise, yet it is widely reported that existing interpretation methods yield physical properties which vary with frequency, complicating subsequent interpretation of test data. Previous research has indicated that much of this apparent frequency dependency occurs due to compliance of the drive system. In this study the linear elastic model of the resonant column apparatus is adapted to include a new drive stiffness parameter, supported by finite element analysis of the drive system. A novel calibration method is presented based on this drive compliance model. Thirteen calibration bars and three added masses are used to conduct an extensive calibration exercise for both a Hardin- and Stokoe-type resonant column apparatus. The novel calibration method is compared with three existing methods in the literature. Limitations of the four methods are identified and discussed. The drive compliance model and its associated calibration method is shown to be a robust means of characterising the apparatus behaviour whilst successfully eliminating frequency-dependency of the calibration parameters. The model is valid where total system damping is small and is particularly valuable when testing stiff specimens where common apparatus assumptions may not apply.