Numerical investigation of the time dependence of shaft capacity of jacked piles in clay

This paper presents a numerical study of jacked piles in clay using the Press-Replace Method (PRM) in finite-element (FE) simulations. The numerical approach allows simulation of pile installation, equalisation and load testing phases in a single analysis. The clay is modelled using a rate-dependent elasto-plastic constitutive model, Creep-SCLAY1S, which can capture destructuration of the clay adjacent to the pile shaft (due to large strains imposed during installation) as well as the coupled non-linear time dependence of effective stress changes during equalisation prior to load testing. Results from laboratory pressure chamber experiments using model piles installed in saturated reconstituted clay samples are first presented and used to verify the adopted numerical approach. Parametric analyses are subsequently performed to investigate the effects of clay sensitivity (structure) and creep on the time dependence of shaft friction. The results show that the rate of gain in shaft capacity with time is greater for sensitive clays and clays with a higher tendency to creep. It is also found that, although the more sensitive clays generate lower shaft frictions when installation-induced excess pore pressures are not fully dissipated, their long-term (aged) shaft capacities can be higher than those for less sensitive clays.