Abstract: The foundations of offshore wind turbines(OWTs)are often subjected not only to complex combination loads, but also subjected to the local scouring. To investigate the effects of the local scouring on the bearing characteristics of the monopile-friction wheel composite foundations under combined V-H loads, a series of indoor model tests are carried out based on indoor water tank test devices. The load-displacement curves are obtained for the composite foundations with and without scouring. After dimensionless treatment and curve fitting process, the envelopes of the bearing capacities and the corresponding simplified formulas are also obtained. The results show that: the vertical and horizontal bearing capacity of the composite foundation can be reduced by about 12.1% and 26.9%, respectively. Further analysis shows that there exists an optimal pre-vertical load(V)which significantly enhances the ultimate lateral bearing capacity of the composite foundation. Additionally, the envelope shrinks inward under scouring conditions. The proposed empirical formulas can be used as a reference for engineering practice.

Key words: offshore wind turbines foundation, monopile-friction wheel composite foundation, local scouring, combined loads, bearing capacity envelope