Abstract
Hybrid foundations are a promising alternative to conventional monopile for offshore wind turbines operating in complex marine environments. The plate-monopile hybrid foundation, formed by attaching a steel plate at the mudline of a monopile, has attracted considerable attention due to its simple structural configuration and good compatibility with existing construction systems. Its mechanical response is governed by multiple factors, including soil conditions, foundation geometry and loading characteristics, yet the underlying mechanisms governing their effects on foundation behaviour remain insufficiently understood. This study combines 1g model tests and finite element analyses to systematically examine the effects of sand relative density (RD), plate-to-pile diameter ratio (R), and cyclic loading amplitude (η) on the cyclic performance of plate-monopile hybrid foundations. The results show that the peak deflection of the plate-monopile hybrid foundation gradually decreases and eventually stabilises with increasing loading cycles, while the cyclic stiffness continuously increases. Increasing the sand RD and R effectively improves the cyclic performance of the hybrid foundation, although the associated benefits exhibit diminishing marginal returns. The influence of η on the foundation response depends on the sand RD and is more pronounced in loose and medium-dense sand. Moreover, increasing the R enhances the load-sharing effect of the plate, thereby reducing the internal forces in the pile, with a more pronounced reduction in bending moment than in shear force. A larger R also promotes load diffusion, optimises the soil stress distribution, and more effectively alleviates local stress concentration under high RD conditions. These findings provide useful insights for the design and optimisation of plate-monopile hybrid foundations in offshore wind engineering.
•The combined experimental-numerical framework for plate-monopile hybrid foundation is established.•The effects of relative density, plate-monopile diameter ratio, and loading amplitude on the structural response are analysed.•The effects of relative density, plate-monopile diameter ratio, and loading amplitude on the soil-pile interaction are analysed.
