Cyclic p-y Plasticity Model Applied to Pile Foundations in Sand

The lateral response of pile foundations in sand is commonly analyzed using the beam on nonlinear Winkler foundation (BNWF) assumption, with load transfer behavior often characterized by the API sand p-y relationship (where p is lateral resistance, and y is relative displacement between the soil and pile). This relationship was developed for static loading conditions, with cyclic correction factors intended to represent degradation due to many slow loading cycles. However, the model is often applied for dynamic loading conditions (e.g., earthquake shaking) because suitable alternatives have not been formulated. This paper demonstrates that the API sand functional form is not ideal for dynamic analysis of piles, and presents a new functional form that better captures the nonlinear p-y behavior of piles in sand during earthquake loading. The new functional form is developed using bounding surface plasticity theory and implemented in an open-source finite-element modeling platform that is freely available to users. The proposed p-y model is shown to capture the experimental response of a pile from a centrifuge test program using calibrated model parameters.