Mechanism-based Interpretation of Soil Arching in Piled Embankments Based on Compression–Extension Zoning

Abstract

The behavior and design of piled embankments constructed on soft soils are governed largely by soil arching, defined as the redistribution of stresses from yielding zones to adjacent non-yielding regions resulting from stiffness contrasts between pile-supported and unsupported areas. Lateral spreading also constitutes a significant component of the load redistribution within the embankment. Arching is characterized by the spatial distribution of the lateral earth pressure coefficient (K). K-contours delineate the compression (K > K₀) and extension (K < K₀) zones, while the K₀ isoline defines the interface between these regions and thereby represents arch geometry. This study employs full-scale finite element modelling to investigate arching development while accounting for lateral spreading in both high- and low embankments. Results show a transition from shear-plane arching at low fill heights to partial and ultimately full arching beyond a critical height, after which further increases in fill height have limited influence on arch geometry. Extraction of K-fields from FEM highlights the governing role of system deformation in stress redistribution. A parametric comparison between FEM and analytical design methods across varying pile spacings and embankment heights reveals stage-dependent arching evolution, characterized by an initial sharp decrease in stress reduction ratio followed by gradual stabilization as embankment height increases. Among the analytical methods, Hewlett and Randolph and BS8006-1 show the closest agreement with FEM trends. The commonly accepted equal settlement plane concept is shown to be valid primarily for closely spaced piles, whereas for wider spacings, differential settlements persist well above the critical embankment height.