Frequency domain response of the lateral vibration of offshore defective pipe piles considering pile–soil–water coupling effects

To investigate the lateral dynamic characteristics of defective pipe piles in offshore environments, this study develops a new framework to obtain a frequency-domain analytical solution for the lateral coupled vibration of defective pile–soil–water systems considering vertical static loading. The soil resistance inside and outside the pile calculated via Biot’s theory and the dynamic water pressure is calculated using of radiation wave theory. The pipe pile is modeled as an Euler beam, with the lateral dynamic impedance at the pile head determined using continuity conditions applied at the pile–soil and pile–water interfaces. The accuracy of the analytical solution is validated, and the study delves into the effects of pile defects, soil layers, water, and vertical loads on the lateral dynamic impedance of piles. The results indicate that external diameter necking defects and modulus reduction defects have the most significant impact on lateral dynamic impedance. Defects located in shallow soil layers at a certain depth from the water–soil interface have the greatest influence on pile head lateral dynamic stiffness (PHLDS), with longer defects having a greater impact. Reinforcing weak shallow soil layers can enhance the pile’s resistance to lateral deformation. The influence of water and vertical static loading on the pile foundation’s dynamic impedance exhibits a synergistic effect. In pile foundation design, defects in pile sections near the water–soil interface should be strictly avoided.