Time-dependent bearing capacity of a jacked pile: An analytical approach based on effective stress method

Abstract

Complex stress changes occur in the soil adjacent to a jacked pile during pile installation, equalization and loading, but the corresponding effects on the bearing performance of the jacked pile are not well understood at present. This paper performs a theoretical study on the time-dependent bearing capacity of a jacked pile by considering the entire stress history of the surrounding soil. The pile installation process is modeled by the undrained expansion of a spherical cavity at the pile tip and a cylindrical cavity around the pile shaft, respectively. A K0-based anisotropic modified Cam-clay (K0-AMCC) model is employed in the cavity expansion solution to evaluate the stress state of the surrounding soil immediately after pile installation. The dissipation of the jacking-induced excess pore water pressure is modeled by the governing equation of radial consolidation theory. The change of the effective stress in the surrounding soil is obtained by solving the governing equation and taking the soil relaxation effects into consideration. A time-dependent empirical reduction factor is introduced to incorporate the thixotropic effect on the friction angle between the soil and pile interface. An analytical approach, based on the effective stress method, is presented to predict the time-dependent bearing capacity of published centrifuge model pile tests and field pile tests. The predicted results agree well with the measured data. It demonstrates that the present approach can be applied to capture the time-dependent bearing capacity of a jacked pile in clay effectively.