Analytical Quantification of Ultimate Resistance for Sand Flowing Horizontally around Monopile: New p-y Curve Formulation

Driven by the need to enhance the performances of the Winkler model when dealing with large-diameter monopiles, the primary objective of this paper is to propose a new p-y formulation that has the ability to realistically model the stiff behavior of monopiles. At first, works revolving about the determination of the ultimate resistance of piles in sands were examined. It was found that the American Petroleum Institute's ultimate resistance for a shallow depth was found suitable to model the soil reaction near the monopile head. However, all proposed methods for the ultimate resistance at large depths were empirical and significantly overestimate the sand stiffness with depth. Taking advantage of the monopile problem geometry that is axisymmetric subjected to nonaxisymmetric loading, an expression giving the soil reaction against a rigid moving disc was established using the semianalytical finite element approach. By extending the obtained formula to failure using some fundamental notions of basic soil mechanics, the ultimate resistance for depths greater than one diameter was rigorously quantified. A totally new p-y formulation encompassing a new p-y shape and a new initial stiffness was proposed and encoded in an existing Winkler computer program. The results of the new formulation were validated by the study of three case histories from the literature.