Finite element analysis of pile installation using large-slip frictional contact

This paper presents some observations on stress and displacement characteristics during the installation and loading of pushed-in piles. A commercial finite element code with the capability of simulating large-strain frictional contact between two or more solid bodies is used to simulate the pile installation and pile loading. The soil is treated as a modified Cam clay material, whereas the pile is treated as a rigid body. The computed total resistance and shaft resistance during pile installation are first compared with measured values from centrifuge tests, which indicates that the total resistance is well predicted by the finite element model, but not the shaft resistance. The difference between the computed shaft resistances and the measured values is mainly due to the cone effects introduced in the finite element model. The computed stress paths indicate that both the mean and deviator stresses first increase when the pile cone is above or at the level of the observation point in the soil, and then decreases once the pile cone has moved below the observation point. When the soil is represented by the modified Cam clay model, a thin layer of soil of one pile radius immediately around the pile, extending from the ground surface to a distance of one pile radius above the pile cone, is under elasto-plastic expansion. Just outside this expansion (softening) zone, a compression zone of a 'U' form is observed. The characteristics of the stress paths and volumetric behaviour are not significantly affected by the initial OCR of the soil. The volumetric behaviour is however strongly affected by the constitutive model used for the soil. The so-called h/R effect is also well captured by the finite element model.