Set-up effect of large-diameter open-ended thin-walled pipe piles driven in clay

A finite element method (FEM) model was developed to investigate the distribution and dissipation of the soil excess pore water pressure (EPWP) around large-diameter open-ended thin-wall steel pipe piles (LOTPs) driven by impact loads into saturated clay, in addition to the set-up effect of LOTPs. The initial pore water pressure (PWP) distribution and vertical bearing capacity of LOTPs after EPWP dissipation were analyzed through this numerical model. The EPWP mapped onto the FEM model was compared with previously reported distribution curves, revealing that the numerical results were generally similar to those of previous theoretical models. Following dissipation for 28 days, the load-settlement curves of LOTPs were compared with the results of several specifications; this indicated that the larger the LOTP diameter, the greater the similarity between axial bearing capacities calculated via the FEM model and the specifications. This FEM model could generally satisfy the re-quirements for analyzing the set-up effect of LOTPs. It was also found that the LOTP capacities were over-estimated when the EPWP was neglected. Beyond 28 days, the pile bearing capacity did not increase because the dissipation of the EPWP was almost fully developed. An equation for predicting the set-up effect of LOTPs installed using impact hammers is also presented.