Fully Coupled Consolidation Analysis of Shear Strength Mobilization and Dragload of a Pile Subject to Negative Skin Friction

Abstract

Mobilization of negative skin friction (NSF) along a pile shaft increases the axial load (dragload) and pile head settlement (downdrag) of the pile, which may exceed the structural capacity of the pile and violate its serviceability performance, respectively. Therefore, the dragload estimation is essential for a pile embedded into a settling ground, where NSF is very likely to occur. This paper presents the results of a series of fully coupled consolidation numerical parametric studies of a pile embedded into a consolidating ground. The investigation focuses on the influences of pile geometry, ground compressibility, and loading condition on pile responses. The soil compressibility and time to apply the pile head load are found to have little influence on the degree of skin-friction mobilization in the long term. The long-term neutral plane (NP) lies within the 60–70% range of the pile embedded length when the pile head load is absent. The presence of a head load shifts NP upward, and the amount of upshift increases with decreasing pile diameter and length. A simple design chart is proposed to estimate the skin-friction distribution in the long term in cases where the pile head load is absent. Finally, an illustrative example is provided to demonstrate how the chart is used and performs. The study offers practicing engineers a simple and quick approach to estimating the dragload of a pile subject to NSF.