Combined effects of long-term cyclic loading and unidirectional flow induced scour on the mechanical responses of tetrapod jacket foundation supported offshore wind turbines

Abstract

To avoid the complexities of constructing embedded rock piles, large diameter pile jacket foundations have recently been employed for deploying offshore wind turbines. The offshore wind turbines endure the long-term effects of complex marine environmental factors, including the combined effects of complex lateral loads and local scour, which pose significant challenges to their bearing capacity and deformation control. This paper presents a series of flume model tests for a tetrapod jacket foundation-supported offshore wind turbine considering the large-diameter characteristics of the base piles. A compact and reliable loading device is utilized to synchronously apply long-term cyclic lateral loading and unidirectional flow induced scour. The mechanical responses of the superstructure-foundation system and the local scour development are investigated, with special attention given to long-term cumulative deformation, natural frequency migration, ultimate bearing capacity, and scour depth development. By comparing these findings with a previous experiment for monopile conducted by the authors, the observed phenomena in this paper are explained and analyzed. The results of this study will enable more precise evaluations of the long-term mechanical responses of a newly installed large diameter pile-jacket foundations supported offshore wind turbines.