Numerical Study on Buckling of End-Bearing Piles in Soft Soil Subjected to Axial Loads

End bearing piles are commonly used as an efficient foundation system for supporting structures built on soft soils. Although, soft soils can provide some confinement to the pile not to be treated as an Euler column, the excessive large lateral movement may cause the soil to fail under axial loads before reaching the buckling load. Moreover, the buckling resistance of end bearing piles under loading-unloading conditions may be influenced since residual stresses in the structural elements of the piles and the surrounding soil exist even after removing the load. In addition, buckling of end bearing piles under extreme loading conditions of loading-unloading nature may result in residual stresses in the structural elements of the piles and the surrounding soil even after removing the load. In this paper, a 3-D numerical model utilizing the finite difference method was developed to study buckling behavior of end bearing piles. First the model's calculated buckling load was verified against the theoretical solution for an idealized Euler's case. Then, a comprehensive parametric study was performed to understand the effect of both the soil stiffness and the flexural stiffness of the pile on the behavior of buckled end bearing piles under both loading and unloading conditions. The results showed that both the lateral stiffness of the supporting soil as well as the flexural stiffness of the pile have a significant impact on the buckling length and hence the buckling load. The flexural stiffness of the pile should match (be relatively close) the stiffness of the soil in order to avoid high values of lateral displacement of the pile's axis.