Numerical Analysis of a Jacked-In Pile Installation in Clay

In this paper, a small strain numerical procedure, the press-replace method (PRM), is adopted to model the monotonic, quasi-static installation of a jacked-in pile under an undrained condition. Numerical simulations are carried out using the small-strain geotechnical finite-element software PLAXIS 2D (version 20.03.00.60). The PRM implementation for modeling jacked-in pile installation is described. This paper aims to demonstrate and assess the prediction potential and limitations of the PRM for modeling the pile installation process followed by the subsequent load testing, using published information from two well-known field case studies. It is shown that the combination of the PRM with the modified Cam-clay constitutive model can not only capture the penetration resistance experienced by the pile during jacking but also simulate realistic stress and pore-pressure changes around the pile caused by the jacking process. The pore-pressure response during postinstallation consolidation, which leads to the pile setup phenomenon, can also be reasonably captured. Subsequently, the importance of incorporating installation effects in the numerical simulations of pile load tests is demonstrated, using a wished-in-place (WIP) pile model and another with the installation process simulated via the PRM. The PRM model predicts a significantly higher pile capacity than the WIP model. The different load-settlement behavior of the two piles can be attributed to the different soil states present in the two models at the start of the load test, in which the WIP model does not capture the changes occurring in the stresses, overconsolidation ratios, and void ratios of the surrounding soil caused by the pile jacking process.