Negative skin friction on single piles and pile groups

Abstract

In the present study, centrifuge model tests have been conducted to investigate the combined effects of NSF, dead load as well as transient live load on an end-bearing pile. An elaborate test control scheme has been developed to seamlessly incorporate 7 sequential test stages into each model test to induce NSF on the instrumented pile through 3 typical means, namely re-consolidation of remolded clay after pile installation, ground water drawdown as well as surcharge loading. The centrifuge model study was subsequently extended to pile groups comprising 3, 5, 9 and 16 piles connected by a rigid pile cap. The subtle difference in the induced dragload among piles in a group as well as the group effects of NSF were qualitatively explored in a consistent and rigorous manner. Numerical analyses on single piles and pile groups subjected to NSF using both axisymmetric and 3D Finite Element Method (FEM) have also been conducted. The axisymmetric and 3D numerical tools, carefully calibrated using centrifuge data, were subsequently applied to the further in-depth investigation of some important issues revealed by the present centrifuge model tests.