Energy flux analysis for quantification of vibratory pile driving efficiency

In this paper, the energy flux in a pile modeled as an elastic shell, is studied theoretically and experimentally. Based on this analysis, a new procedure is proposed to quantify the pile installation efficiency. This procedure is of importance for vibratory installation of the foundations of offshore wind turbines and it is believed to be the first procedure that relies directly on the energy propagating down the pile rather than the energy supplied by the vibratory shaker. The proposed approach is tested on piles installed by two distinct vibratory techniques, i.e. the axial vibratory driving and the recently developed Gentle Driving of Pile (GDP) method. The field data obtained during an experimental campaign were analyzed with the proposed energy flux approach. The cumulative energy flux in the pile normalized by the energy input of the shaker is found to be the best measure for quantification of the installation efficiency. Correspondingly, the main proposition of this paper is that the installation efficiency will be maximized provided that the normalized cumulative energy flux is at its maximum.