Monopiles are widely used as the foundation to support offshore wind turbines (OWTs). The response of monopile supported OWTs is strongly affected by the natural frequency of the system relative to the load spectrum, and in turn the natural frequency is governed by the initial stiffness of the foundation. Both fatigue limit state (FLS) and serviceability limit state (SLS) design are also influenced by the foundation stiffness. The stiffness of the foundation during operational loading is a function of the ‘initial’ soil state post-installation, which is influenced by the installation effect. This is the first of a pair of companion papers that investigates the effect of different installation methods on the subsequent response of monopile under lateral loading through extensive numerical analysis. The present paper focuses on quantification of the effect of pile installation on the soil states in sand for three different initial relative densities. The numerical model is first validated against purpose-designed centrifuge tests. Subsequent analyses demonstrate how the soil state, including the void ratio and stresses, is altered from in situ conditions during pile installation, and are markedly different depending on whether the pile is jacked or impact driven. The results presented here and in the companion paper highlight the need to account for the effects of the installation process on the lateral pile response.
|Journal||Journal of Geotechnical and Geoenvironmentral Engineering|
|Publication status||Accepted/In press - 20 Oct 2020|