P-Y Lateral Pile Analyses Accounting for Arbitrary Loading Directions and Calibration Uncertainty-Article

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The paper presents a bounding-surface plasticity p-y model for analyzing laterally loaded piles under monotonic, cyclic, and multidirectional loading. Extending the traditional API method, it represents resistance in two orthogonal directions with a single spring at each pile node, enabling three-dimensional loading analyses while accounting for hysteresis, accumulated plastic deformation, and energy dissipation without artificial damping.<br /><br />The model is calibrated to the API monotonic p-y response using familiar soil inputs. Its performance is assessed through back-analyses of nine full-scale piles at the Cowden site, covering three pile diameters and a range of embedment ratios. Monte Carlo simulations explore uncertainty in soil strength and stiffness profiles and help identify a common strength profile for the different test piles. The resulting analyses generally reproduce observed monotonic and cyclic pile responses. They also show that predictions are strongly influenced by soil-strength assumptions, while some observed behavior—particularly stiffness changes associated with pile-soil gapping—is not captured.<br /><br />For hypothetical biaxial loading, the model predicts asymmetric responses, stress-induced anisotropy, plastic displacement accumulation, and energy dissipation. These responses compare favorably with plane-strain continuum finite-element analyses and available small-scale physical tests.<br /><br />The author concludes that the method is computationally efficient, practical for engineers familiar with p-y analysis, and suitable for complex loading histories. Its validation is strongest for the Cowden site and relies partly on illustrative biaxial analyses, so further experimental data would help confirm its performance under multidirectional loading.

Keywords

bounding-surface plasticity

p-y model

laterally loaded piles

cyclic loading

multidirectional loading

biaxial loading

API method

hysteresis

Monte Carlo simulation

pile-soil interaction