Behavior of Pile in Cohesive Soil Subjected to Combined Vertical and Lateral Load Considering P-? Effect-Paper

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The study examines piles embedded in homogeneous clay and subjected to combined axial and lateral loads. It uses a Beam on Nonlinear Winkler Foundation model, solved with a finite-element approach. Soil nonlinearity is represented by depth-dependent p–y curves, and P–Δ effects are included to capture additional moments caused by pile deflection under axial load. The analysis is implemented in MATLAB and validated against published field-test results, with satisfactory agreement.<br /><br />The results show that axial compression increases pile-head deflection and, when P–Δ effects are considered, reduces lateral load-carrying capacity. The reduction is particularly pronounced for piles with larger slenderness ratios. Greater soil cohesion increases lateral capacity, while increasing pile slenderness generally reduces pile-head deflection and shifts behavior from rigid to flexible. Piles with L/D ≤ 20 behave as rigid piles, those with L/D ≥ 30 as flexible piles, and intermediate ratios produce transitional behavior. For rigid piles, the rotation point is approximately 0.7 times the pile length, largely independent of pile stiffness. For flexible piles, the depth of fixity increases with the pile-to-soil stiffness ratio.<br /><br />The findings provide a numerical framework for assessing pile response in clay under combined loading and emphasize the importance of accounting for P–Δ effects in design.

Keywords

pile response

combined loading

homogeneous clay

beam on nonlinear Winkler foundation

finite element analysis

p-y curves

P-Delta effects

lateral load capacity

pile slenderness ratio

MATLAB modeling