This thesis presents numerical, and semi-analytical approaches for the analysis of laterally loaded piles based on the Matlock p–y formulation for soft clay, following the recommendations of the Swedish Pile Commission.

A comparative analysis was first conducted, benchmarking three solution approaches: Numerical p-y formulations in RFEM 6 integrated with a Python-based application programming interface (API), the finite element (FE) toolbox CALFEM and a semi-analytical solution. The different approaches adopts different level of complexity, and produced stable results. The semi-analytical solution provides a practical and conservative solution for small load levels where linear elastic soil behaviour can be assumed, but is not recommended for larger loads where the soil response enters the nonlinear range. The iterative secant solution procedure implemented in CALFEM, captures both nonlinear soil behaviour and second-order effects, proved to be computationally efficient, providing stable results while maintaining good agreement with the RFEM 6 results across various loading levels .

An automated numerical framework has been developed in Python using the RFEM 6 API for the analysis of laterally loaded piles. The framework implements the p–y method and accounts for nonlinear soil behaviour through lateral springs, second-order effects, and geometric imperfections derived from the first buckling mode of the interacting pile–soil system. Using the framework, a parametric study was conducted to investigate the influence of soil conditions, axial and lateral loading, and pile-head boundary conditions on second-order effects and the load-carrying capacity of a standard concrete and steel pile section. The resulting bending moments were assessed using normal force–bending moment (N–M) interaction diagrams based on Eurocode provisions. The results demonstrate that second-order effects on the bending moment distribution and section load-bearing capacity for both pile types are strongly affected by pile and soil strength and stiffness characteristics, pile-head boundary conditions, the magnitude of the applied lateral load, and the level of axial compression. In particular, free pile-head conditions, weak soil conditions, and high lateral loads increase pile deflections and amplify second-order bending moments, leading to reduced mobilized soil resistance and a subsequent decrease in the overall load-bearing capacity of the pile–soil system. Once the limiting lateral soil resistance is reached, further pile movement occurs with limited additional soil support, resulting in increasing displacements until structural failure, either through the formation of a mechanism or through loss of equilibrium of the system.

The pile–soil interaction problem is highly complex, and careful evaluation of the actual soil conditions, pile-head rotational restraint, and applied load levels is essential for reliable assessment. Furthermore, nonlinear soil behaviour, second-order effects, and initial imperfections should be explicitly considered when analysing slender piles subjected to lateral loading. These factors can significantly influence the predicted analysis outcome compared with simplified approaches that neglect their effects.