Consideration of the influence of pile surface geometry on underwater noise attenuation during pile driving

Abstract This study aims to develop methods for minimizing underwater noise generated by impact pile driving, with a specific emphasis on pile designs less prone to producing such noise. The underwater noise originates from the expansion of the pile due to the Poisson effect as the longitudinal wave propagates through the pile while driving. It was hypothesized that an irregular surface profile of the pile could effectively induce longitudinal wave diffraction and attenuation. Both experimental trials and numerical simulations were conducted to explore how the surface profile of the pile influences underwater noise. During the experiments, driving simulations were performed using test rods, and comparisons were drawn between configurations with and without convex sections. Visual observations revealed the occurrence of oblique shock waves immediately following impact, along with arc-shaped compression waves emanating from the convex sections of the shape, subsequently leading to the formation of bubbles, thus producing compression waves. Simulation findings demonstrated that thicker test rods exhibit greater damping effects, aligning with the experimental outcomes. In the presence of convex sections, the pressure decayed more rapidly, with the pressure value after decay also being smaller compared to conditions lacking convex sections. In conclusion, it is proposed that the shape of the pile could effectively mitigate pressure waves, leading to a significant reduction in underwater noise by generating expansion waves that counteract compressive waves.