Comparison of Downdrag Analyses of Bridge Pile Foundations due to Settlements of Approach Embankment Using Analytical and Finite Element Methods

Highway bridges are critical structures with little tolerance to movement. Consequently, bridges are typically supported on pile foundations to limit the settlement. Approach embankments are prone to settle more than the bridge, especially when embankment is founded on cohesive soil layers. Such consolidation induced settlement generates negative skin friction on the pile foundation—a phenomenon known as downdrag. Downdrag reduces pile capacity and diminishes its ability to limit vertical movement. This paper presents a comparison of two methods available to design for practitioners, the analytical method and the finite element method, in estimating settlements of deep foundations subjected to the downdrag phenomenon. The behavior of soil layers is modeled in a two-dimensional nonlinear finite element analysis using commercial software package PLAXIS2D. A sensitivity analysis is performed on selected input parameters to determine their significance and impact on the convergence. This paper is expected to be of benefit to researchers and practitioners in the field of geotechnical engineering by presenting a correction to the plain strain assumption.