Comparative Analysis of Analytical and Computational Methods for Axially Loaded Piles in Stratified Soils Subjected to Downdrag (#2751)

Authors

Ruiz, Matías

Santiago, Yrene

Araujo, William

Abstract

The Downdrag or negative skin friction phenomenon constitutes a critical aspect in the design of deep foundations, particularly for piles installed in soft or stratified soils, where settlement of the surrounding soil generates a relative downward displacement that induces negative shear stresses along the pile shaft. This mechanism mobilizes an additional load that adds to the applied structural loads and may reduce the available axial capacity of the pile while increasing settlements. Despite its relevance in infrastructure projects founded on compressible soils, the evaluation of Downdrag still presents challenges associated with the complexity of soil–pile interaction and the influence of geometric and stratigraphic variables. The objective of this research is to evaluate the load-bearing capacity and settlements of piles constructed in stratified soils affected by Downdrag through a comparative analysis between traditional analytical methods and computational analysis. For this purpose, 45 case studies representing different stratigraphic configurations and thicknesses of critical cohesive soil layers were analyzed, also considering variations in pile diameter. The computational analysis was performed using the pile module of the GEO5 software, which is based on analytical formulations of soil–pile interaction. The results show that increasing the thickness of the critical cohesive soil layer has a significant influence on pile behavior. Analytical calculations and computational analysis showed high agreement in the estimation of shaft and tip bearing capacity (differences lower than 2.5%). However, settlement predictions exhibited larger discrepancies, highlighting the influence of soil stratigraphy, the thickness of cohesive layers susceptible to settlement, and pile diameter on the development of Downdrag.