Finite Element Study of Vertical Load Transfer for Settlement Analysis of Suction Piles

Abstract

An important part of the caisson foundation design is the determination of long term settlements. As the caisson foundation usually supports subsea structures, such as gas pipes, manifolds, etc., it is crucial to determine the final displacement. Understanding the mechanism of transferring the vertical load of a caisson foundation to the soil is an essential task in order to evaluate the con-solidation settlements.

In this report, the stress distribution mechanism were analysed by using the finite element meth-od. The numerical analysis was performed using the finite element method code Plaxis 2D. The soil parameters were based on laboratory tests. Three different soil models have been evaluated; The Soft Soil-, the Hardening Soil- and the Hardening Soil Small-Strain model. All these models were used as material models to analyse the soil behaviour, except for the interface zones where the Mohr-Coulomb soil model was utilized. In an attempt to estimate the long term settlements, this thesis presents results of numerical consolidation analysis, in which the remoulded zones adjacent to the caisson skirt wall has been taken account for.

The set-up effect has been accounted for, by adequate modelling of time dependent increase of shear strength. As a consequence of the highly mobilized skirt wall friction, the final settlements strongly relate to the interface shear strength. The modelled undrained shear strength has a great effect on the numerical results, due to the mobilization of the surrounding soil. Comprehensive evaluation of the soil- structure interaction is important in order to validate the FEM-model.