Comments on the Current and Future Use of Pile Dynamic Testing

ABSTRACT: Impact driving of piles is a complex process which depends on the interaction of the stress wave progressing down the pile and on the dynamic soil resistance along the shaft and at the toe. Pile driving vibrations can adversely affect adjacent structures, and the intensity of ground vibrations depends on the dynamic resistance along the pile rather than on the energy applied to the pile. The viscous damping factor, Jc, is one of the fundamental parameters when the static pile resistance is determined from dynamic tests. Theoretical analyses and field observations show that the Jc-factor is not solely a soil parameter, but a function of the ratio of pile impedance and soil impedance at the pile toe. Consequently, the pile toe damping factor for an open-toe pipe pile would be different when no plug develops in the pile and when the pile toe is fully plugged. Moreover, the mentioned aspect needs to be considered when the results of a test pile of one pile type are applied to a construction pile of a different type. Viscous damping along the pile shaft and at the pile toe is the source of ground vibrations. The vibration magnitude is governed by the interactive nature of dynamic pile-soil resistance, which is a function of the ratio between the pile impedance and the soil impedance for P-waves. It is shown that the vibration transmission efficacy and the dynamic resistance are inversely linearly proportional to the pile impedance, and that energy transmission efficacy correctly reflects the vibration emission from the pile t