Numerical modelling of laterally loaded piles in clay

The rapid expansion of the offshore wind industry in recent decades has led to an increased scrutiny of methods traditionally used to design piles in the offshore environment. Investigations by the industry have been performed using a multitude of methods including finite element analysis (FEA), centrifuge testing, and large scale field testing. In this thesis, a novel numerical technique termed finite element limit analysis (FELA) is used to investigate the limiting capacity of laterally loaded piles in clay and the mechanisms that contribute to this resistance. Finite element limit analysis is a modelling technique that permits rapid optimization-based analysis of plastic collapse mechanisms of boundary value problems with complex loading, structural geometry and soil parameter profiles. Unlike traditional FEA where the accuracy of a given solution is unknown, FELA provides lower and upper bound solutions between which the exact solution must lie within a known bracketing error. An additional benefit of FELA is that runtimes are significantly shorter than equivalent FEA models allowing large parametric studies to be performed in a fraction of the time. Methods previously used for predicting ultimate resistance are revisited and compared to FELA; such as the moment equilibrium method used by Broms (1964) to calculate total capacity and the widely used Matlock (1970) methodology for determining p-y curves in clay. Relationships between key dimensionless groups of geometry and soil parameters are explored and recommendations about pile capacity are provided. Soil strength profiles including homogeneous conditions, strength gradients and abrupt changes in strength are considered, with recommendations provided on predicting the profile of limiting resistance in each case. An update to the traditional moment equilibrium approach for calculating pile capacity is proposed incorporating additional resistance mechanisms such as shear and moment resistance at the pile base, and a distributed moment resistance acting on the shaft of the pile. Finally, some case studies demonstrating use of the recommendations are presented with a comparison to some of the recently performed pile tests in the PISA joint industry project as a check on the validity of the proposed approach.