GTC attended  the 1st Vietnam Symposium on Advances in Offshore Engineering (VSOE) in Nov 2018, and  presented A New Calibration Technique to Improve Data Reduction for Stokoe Resonant Column Test:

 

When testing of stiff soil specimens using a Stokoe resonant column apparatus (RCA) the compliance of the apparatus significantly influences the derived stiffness of the soil. In this paper, we present a simple mathematical model that takes into account equipment compliance, and therefore improving the accuracy in derivation of the small strain shear modulus of soils tested using a Stokoe RCA. The model utilizes the simple harmonic motion of two springs in series to derive the equations of motion; one spring represents the equipment torsional stiffness, while the other spring represents the unknown soil stiffness. The apparatus torsional stiffness can be determined experimentally with a series of aluminium calibration bars. A finite element model was developed to validate the ‘two-spring’ model, confirming that the ‘two-spring’ model was able to significantly mitigate equipment compliance when determining specimen stiffness.”