The foundations of offshore wind turbines are often subjected to horizontal load (H)

bending moment (M)

and vertical load (V). The monopile-friction wheel hybrid foundation is an innovative type of foundation for offshore wind turbine

which combines the advantages of both monopile foundation and gravity foundation. In order to investigate the bearing characteristics of the monopile-friction wheel hybrid foundation under combinedloading conditions

a series of model tests were conducted based on the in-house designed experimental equipment. The horizontal load-displacement curves and the bending moment distributions of the pile shaft were determined under different V-H loading conditions in stiff-over-soft soil deposits through model tests. By dimensionless treatment and fitting process

the envelopes of bearing capacity and the corresponding simplified formula were obtained. Then

based on the model tests

several groups of numerical models were established

and numerical simulations were conducted for parametric analysis. Results show that the bearing performance of the monopile-friction wheel hybrid foundation underV-H loading conditions was significantly improved compared with that of the monopile foundation in stiff-over-soft soil deposits. The pre-applied V had the most obvious enhancement effect on the horizontal and bending moment bearing capacities of the foundation when it reached about (0.5-0.6)Vu under V-H combined loadings. In engineering practice

the relationship between the loading conditions and the computed failure envelopes can provide guidance for foundation design

and the bearing performance of monopile-friction wheel hybrid foundation can be evaluated through the empirical formula proposed in this study.