Ground motion reduction in vibratory pile driving via axial and torsional vibrations

In this paper, the characteristics of the induced ground motion are studied for two pile installation methods. Specifically, the classical axial vibratory driving is compared with the Gentle Driving of Piles (GDP) method, to investigate the effect of high-frequency torsional excitation in the soil response. For that purpose, a non-linear 3-D axisymmetric pile-soil interaction model - benchmarked against field data for both methods - is used to perform the numerical study. The friction redirection mechanism, that is mobilized due to the torsional excitation in GDP, leads to a different wavefield in the soil medium compared to axial vibro-driving. In the latter only SV-P wave motions are elicited, whereas torsion introduces SH wave motions as well. For the numerical study, the model is comprised by a thin cylindrical shell coupled with a linear elastic layered half-space through a history-dependent frictional interface. The Thin-Layer Method (TLM) coupled with Perfectly Matched Layers (PMLs) is employed to accurately describe the wave motion in the soil medium. Comparisons in terms of the peak particle velocities (PPVs) and soil particle trajectories showcase significant motion reduction due to redirection of the soil friction forces, which elicits high-frequency SH waves and reduces the SV-P wave motion.