The Stokoe resonant column apparatus: effects of stiffness, mass and specimen fixity

This paper reports the results of a series of analyses, and physical and numerical experiments, carried out in order to investigate the effects of apparatus stiffness and mass, and specimen fixity, on the results obtained from fixed–free resonant column testing. It is shown that the stiffness of the drive head and the mass of the apparatus base can both have a significant effect on the results obtained from tests on stiffer geomaterials. Connectivity between the specimen, the apparatus base and the top cap is also an issue. Methods of recognising and determining the magnitudes of these effects are described, and recommendations are made for their evaluation and control.