Dynamic response of super-large-diameter steel casing under axial impact load

With the increasing diameter of deep-water bored piles, the risk of buckling deformation of super-large-diameter steel casings (SLDSC) during the dynamic impact driving process has increased dramatically. However, the risk factors involved in this process are yet to be ascertained. This study is based on the Xihoumen Rail-Road Bridge project, in which the steel casing used in the pile foundation has a design diameter of 6.8 m. LS-DYNA simulation software was used for numerical modelling. The influences of factors such as the casing wall thickness, hammering output energy, and the initial defect ovality were considered. The stress response, displacement depth (z-displacement), and buckling characteristics of SLDSC under axial impact load were studied. The reliability of the numerical modelling was also verified. The results show that for thin walls, the generated axial stress is great, and it is likely that buckling deformation can occur, thereby making it more difficult to drive the SLDSC to the designed depth. Relatively small hammering energy is insufficient to drive the SLDSC to the desired depth. As the hammering energy continues to increase, the increasing rate of z-displacement drops, and it is more likely to trigger non-axisymmetric buckling and curling of the SLDSC. For great initial defect ovality, the non-axisymmetric axial critical stress is small and is likely to trigger deformation accidents of the SLDSC, in which the buckling characteristics develops along the initial defect. Finally, for SLDSC used in relevant projects, it is recommended to have a wall thickness of 74–76 mm and hammering output energy of 1800–2000 KJ to control the ovality below 30 mm during manufacturing and transportation. The research results can provide a theoretical basis for the reasonable determination of wall thicknesses for SLDSC, the usage and debugging of special hammering equipment, and the control of defects during the manufacturing and transportation processes, thereby reducing the risks of buckling and deformation accidents during the axial impact driving process. • LS-DYNA was used to analyse the stress response, displacement, and buckling of SLDSC in the dynamic impact driving process. • For small wall thickness, the generated axial stress is great, and it is likely that buckling deformation can occur. • When the hammering energy increases to a certain level, the increasing rate of z-displacement drops. • For great ovality, the non-axisymmetric critical stress is small, and it is likely to trigger the deformation accident.