Load transfer model for vertically loaded non-circular piles

Abstract

The load-transfer (LT) method, involving a series of ‘t-z’ springs to represent pile shaft-soil interaction and a ‘q-z’ spring to represent pile tip-soil interaction, is widely used to model the load–displacement behaviour of vertically loaded piles. While a plethora of LT models have been proposed for piles with circular cross sections, they are not directly applicable to non-circular (NC) cross sections. Therefore, there is a lack of tailored solutions for rectangular, H-shaped and X-shaped piles even though they are common in geotechnical practice. The aim of this paper is to develop a general theoretical framework for the construction of LT curves for NC piles. This framework allows NC piles with any cross section to be considered. The LT curves for NC piles are formulated using a two-parameter hyperbolic model which requires input of (a) the initial elastic LT stiffness and (b) the unit ultimate shaft friction. The elastic stiffness for vertically loaded NC piles with arbitrary cross sections is described using a rigorous semi-analytical (SA) solution involving variational principles. A nonlinear numerical solution for the pile governing equation with the incorporated t-z and q-z curves is achieved using the Runge-Kutta (RK) method. The proposed LT curves are used to construct the pile governing equation and a numerical solution using the Runge-Kutta (RK) method is proposed to predict the responses of NC piles in drained sand. The proposed theoretical LT predictions of pile response are validated through comparisons to elastic–plastic finite element calculations.