The use of laboratory and site tests data in the finite element modelling of offshore piles subjected to tensile loading

The thesis investigate the response of pile foundations subjected to axial load, with application to offshore wind turbines supported by multi-pod steel jackets. Wind turbines are relatively light weight structures as compared to other offshore structures and this results on the foundation in high tensile loadings. For this reason, the thesis focus is the response of a open ended steel pile subjected to pull out. The study develops on the results of a large-scale testing campaign recently conducted at the Test Centre of Support Structures of the Universität Hannover. The model piles encompassed various lenghts, diameters and thicknesses. In the thesis, different design methods (ICP-05, UWA-05, NGI-05 and Fugro-05) have been used to back analyse the experimental results and were compared to each others. Results of site and laboratory tests on the soil used in the experiments were also used to identify the soil parameters required to implement finite element models of the tested piles. In particular, CPT tests and triaxial tests were considered and the parameters derived are the soil behavior type, the soil unit weight, the stiffness modulus, the relative density, the poissons ratio, and the peak friction angle. Finite element analyses were then run in the experimental boundary and loading conditions e the results were compared with experimental data. A good agreement was observed, particularly on the capacity. The advantage of using the finite element method is the possibility to gain an insight in the pile behaviour and describe the entire load-displacement curve, when compared to CPT based bearing capacity prediction. Good results were achieved using a simple constitutive model, improvement can be surely gained by implementing more sophisticate soil models.