ASSESSMENT OF NEGATIVE FRICTION AND OF NEUTRAL POINT IN PILES BY 3D NUMERICAL ANALYSES

Abstract

Negative skin friction (NSF), caused by greater settlement of compressible soil relative to the pile, generates downward shaft shear and dragload. At pile-supported viaduct abutments, this vertical interaction may be accompanied by embankment-induced lateral soil movement, leading to pile bending and horizontal group displacement. This study investigates the combined axial and lateral pile response associated with this mechanism using a floating 5 × 5 pile group subjected to one-sided surcharge in PLAXIS 3D. Piles are represented by embedded beam elements, and NSF development is simulated through consolidation. Dragload, neutral-plane depth, bending moment and lateral displacement are evaluated for each pile from the same analyses. The parametric study examines surcharge magnitude, pile spacing and length, clay thickness, embankment distance to piles, interface strength and pile-head load, with a four-sided surcharge case analyzed as a symmetric reference. Results show pronounced front-to-back differences in dragload and neutral-plane position. Under one-sided loading, bending in the loading direction may govern the structural response while the group translates away from the fill. Thus, pile-supported abutments on soft ground should be assessed as three-dimensional soil–pile–cap systems rather than by considering NSF only as an axial load-transfer problem.