Spyridis, Michail S.;
(2023)
Numerical simulation of the installation and the lateral response of offshore wind turbine monopile foundations.
Doctoral thesis (Ph.D), UCL (University College London).
Abstract
The rate of construction of offshore wind turbine farms is continuously increasing, with monopiles being the extended type of foundation. During the life-period of these infrastructures, the offshore environment induces lateral loads, which are transmitted to the soil. This repetition of the lateral forces results in the accumulation of deformations in the surrounding soil mass. Thus, after a certain point of residual displacements, the operation of the wind turbine stops, as the serviceability limit state has been exceeded. The current design criteria seem to fail to capture the response of monopiles as they are mainly derived for piles with relatively small diameters. The installation of the monopiles, which greatly affects the soils surrounding the piles, are usually neglected in such design procedures. Thus, the research efforts need to focus on the lateral response of large-piled foundations, taking into account the effects of the different installation procedures in the soils. For the sake of completeness, it should be stressed that, in piles of such geometrical characteristics, the properties of the soil mass control their lateral response. Previous research identifies different trends in the evolution of the soil properties around piles during their installation. These effects need to be accurately taken into calculation in the subsequent lateral response analysis. Thus, this thesis aims at correlating the installation effects with the lateral response of monopiles. In more detail, three stages during the life-period of a piled foundation are taken into consideration in this analysis, namely, a) prior to installation, b) during installation, c) during application of the lateral load. It should be pointed out that, in the literature, in general, the installation effects are extensively neglected. Therefore, in this thesis, two different types of numerical models are developed for the analysis of the installation (large deformation) and the subsequent lateral response (small strains). Different assumptions need to be taken for each modelling approach, namely, different constitutive laws and different numerical algorithms. The ultimate objective of this thesis is to investigate the installation effects around single piles focusing on the penetration resistance as well as on the stress-specific volume state during this procedure. Subsequently, a comparative analysis of the lateral response of piles is carried out considering the aforementioned effects. The results demonstrate that the installation effects are crucial to understanding the overall behaviour of the monopile under serviceability conditions and hence cannot be neglected. Both jacking and impact driving installation procedures subject the soil to pre-stress history that overall causes over stiffening, and therefore the lateral response is later on greatly affected. Further research is needed to confirm the general implication of these aspects.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Numerical simulation of the installation and the lateral response of offshore wind turbine monopile foundations |
| Language: | English |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10175787 |
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