Load Transfers During Vibratory Driving

The vibratory driving technique consists in applying a vibratory load onto a profile to reduce the ground resistance and allow penetration of the profile under its own weight. The vibratory action is produced by counter-rotating eccentric masses actuated within the exciter block. A proper definition of this mechanical action is fundamental for vibratory driving analyses. The vibratory force transferred from the vibrator onto the pile during vibratory driving is however generally neither well defined nor understood, in particular when using simplified closed form solutions for the analysis of pile driving. Few authors have pointed out the very low ratio observed between the force measured in the pile and the nominal inertial force developed by the eccentrics, but without offering a theoretical framework to explain and predict this low ratio. The objective of this paper is to develop a better understanding of the so-called ‘efficiency factor’ of the vibratory driving process. Analytical solutions are presented, along with more advanced numerical simulations. Theoretical solutions are illustrated with reference to field measurements collected at different test sites.