Effect of Hammer Shape on Energy Transfer Measurement in the Standard Penetration Test

Abstract

The shape of the hammer used for the Standard Penetration Test is not specified in most existing standards, yet the literature suggests that it does affect the amount of energy transfer. Three cylindrical hammers and a safety hammer in different geometrical configurations are adopted in laboratory experiments to investigate the effect of hammer shape on energy delivered to a drill rod. In the experiments, true free-fall blows are employed. Energy transfer during each blow is measured using a strain-gauged drill rod and a force transducer mounted atop the drill rod. Energy transfer between the hammer and the drill rod is calculated by the stress-wave force integration of the force-time history measured in each hammer impact. Measurement data are all corrected to an infinite rod length condition. With a total of 80 controlled blows for the four hammers, the measured energy transfer ratios are all nearly 99%. The tests performed in this study are fairly repeatable and the measurement data of the two different devices are correlated very well on the basis of wave mechanics. The measurement test results indicate that the effect of hammer shape on the energy transfer of the standard penetration tests presented herein are negligible.