Large-diameter monopiles of offshore wind turbines are subjected to continuous multistage cyclic loads of different types (one-way or two-way) and loading amplitudes over time. The loading history is likely to affect the lateral response during the subsequent loading stage. This paper conducts a systematic study on the lateral response of monopiles with and without reinforcement in multilayer soil. Two groups of monotonic centrifuge tests of monopiles with and without reinforcement are carried out to compare and study the influence of reinforcement on the displacement, bending moment and earth pressure of monopile foundations. Local reinforcement in the shallow layer effectively improved the bearing capacity of the monopile foundation. The ultimate bearing capacity of monopile foundations in monotonic tests provides a load basis for cyclic tests. Four groups of continuous multistage cyclic centrifuge tests of monopiles with and without reinforcement with different cyclic modes and loading amplitudesare carried out to investigate the influence of loading history on the lateral cumulative displacement, unloading secant stiffness and bending moment. Empirical design recommendations for monopiles under continuous multistage cyclic loads with different cyclic modes and loading amplitudes are provided based on the results of the tests.
