Prediction of drag force on piles subjected to negative skin friction induced by bridge embankment construction based on measured field data

Abstract

Piles are structural elements, transferring the superstructure’s loads to competent layers, through skin friction and end-bearing. Surcharge loads application and following consolidation induce downward movement in the soil adjacent to piles installed in a compressible layer. This movement generates negative skin friction (NSF) that acts downward at the pile-soil interface, resulting in an additional axial force added to the shaft and excessive pile settlement known as drag force (DF) and downdrag (DD), respectively. This study aims to evaluate the mobilized DF on a driven H-pile installed in clay till using three-dimensional (3D) nonlinear finite element (FE) analysis. The numerical model was validated against field data from an instrumented H-pile as part of a two-span bridge (Daly Overpass) on PTH10 in Manitoba, Canada. The calculated axial force and water total head indicated good agreement with the measured field data. Parametric analyses examined the effects of pile cross-sectional area, length, material, and applied pile head load magnitude on DF. Results showed that DF and DD values differ for piles within the cap, depending on the geometry and direction of the load application on the piles. For this project’s geometry, the maximum axial force (MAF) applied on the pile due to the embankment construction and following consolidation for the most critical pile location can reach approximately 27 % of the pile total capacity measured at the end of initial driving. Additionally, the DF and DD at the most critical pile location were 25 % and 37.5 % higher than the least critical pile scenario, respectively. Increasing the pile’s cross-sectional area and length led to an increase in DF and a downward shift of the neutral plane (NP). However, increasing the applied dead load on the pile reduced the DF and caused the NP to shift upward toward the pile head. Additionally, more DF was generated along the steel pile compared to the concrete pile.