Experimental study on the sediment movement around monopile under vibration action

Abstract

Offshore wind monopile foundations are subjected to strong wave current nonlinear effects and horizontal vibration loads caused by strong winds, waves, and rotating blades. In order to understand the rule of sediment movement around monopile under different vibration frequencies and amplitude, a cyclic loading test was carried out in the sand tank. The motion and migration rule of sediment particles around monopile under vibration action was observed by color tracer sand. The development process of the subsidence pit was qualitatively described by comparing the typical moment photos of sediment particle movement on the bed's surface with time. The transition zone of sediment particles was observed by vertical cutting of the sand bed. Then, the relationship between the relative time scale T0 and the vibration intensity under pure vibration load is analyzed, and the relationship between the equilibrium settlement depth and the initial settlement rate is obtained. The experimental results show that under vibration loading, the densification of the sand bed around the monopile foundation along the loading direction and the phenomenon of ratchet convective movement is relatively strong, and the relative time scale of settlement shows a tendency to decrease with the increase of vibration intensity; the multi-stage alternating loading of vibration and wave-flow loading will result in the backfilling and widening of the scouring pits; the rise in the amplitude and the frequency of vibration under the joint action of wave-current-vibration will decrease the depth of the equilibrium scouring, and the width of scouring pits will increase significantly with the increase of amplitude, and the backfilling of the sand will be more evident with the increase of the frequency of vibration.