Objective As a key pathway toward developing clean and renewable energy, offshore wind power plays a vital role in mitigating global energy shortages and advancing the "dual-carbon" goals. During operation, rock-socketed foundations of offshore wind turbines are subjected to cyclic horizontal loads caused by wind, waves and currents; However, their deformation behavior remains poorly understood.

Method A field test applying uniaxial bidirectional horizontal cyclic loads was conducted on rock-socketed monopiles, examining the evolution of pile head displacement, shaft displacement and bending moment, surrounding rock resistance, cyclic p-y curves.

Result The experimental results indicate a horizontal ultimate bearing capacity of 60 kN for the rock-socketed monopile. Under progressively increasing graded loads, the pile head rotation angle increased gradually, demonstrating a failure mode typical of a long elastic pile. The evolution of pile head horizontal displacement with the number of cycles followed a pattern characterized by an initial rapid increase, followed by a period of slow fluctuation. Notably, the accumulation of horizontal displacement along the pile shaft occurred predominantly within the first 100 loading cycles across all monitored depths. Furthermore, the pattern of displacement accumulation transitioned from shallow to deeper rock layers as the number of cycles increased. Finally, the cyclic p-y curves exhibited a three-stage evolutionary process: elastic, elastoplastic, and stable.

Conclusion This study establishes a predictive formula for estimating the pile head horizontal displacement of rock-socketed monopiles under long-term cyclic loading, thereby providing a means to analyze their long-term cumulative deformation behavior. Furthermore, a cyclic load analysis method is developed based on the derived cyclic p-y curves. This methodology offers a theoretical foundation and technical support for the optimization of current design codes for rock-socketed piles supporting offshore wind turbines.