Research on Bearing Characteristics of Offshore Inclined Helical Pile-Group Foundations in Sandy Soil

Abstract

[Introduction] The offshore wind power industry is among the most pioneering and strategic emerging sectors in the global development of new energy sources. The research focuses on the inclined helical pile-group foundation, which is currently applied for offshore wind turbines, and systematically studies its load-bearing characteristics. It is of great significance to accurately understand the load-bearing characteristics for the subsequent popularization of this promising new type of foundation and the overall development of the offshore wind power industry. [Method] The effects of various variables, including pile number, pile spacing and inclination angle, on the bearing characteristics of inclined helical pile groups were systematically studied by finite element software, and the change trends of the pile group effect coefficient and bearing capacity with these factors were obtained under various working conditions. [Result] The results show an approximately 15% improvement in the load carrying capacity of inclined helical pile groups compared to monopoles. Additionally, the efficiency coefficient of pile groups increases with a larger pile number. The load carrying capacity of pile-group foundations is positively correlated with pile spacing, as smaller pile spacing leads to a more significant superposition of central soil pressure. The variation in ultimate load carrying capacity remains within about 4% across the value range of pile spacing. Larger inclination angles enhance the compressive load carrying capacity of inclined helical pile-group foundations, causing an increase in their compression efficiency coefficient. Compressive bearing is found to be effective at an inclination angle of 8°. When subjected to pulling action, the upper soil of inclined helical pile groups experiences less disturbance, the foundations' behavior is more influenced by the pile spacing, and the extreme depth of vertical displacement of the soil at the center of the pile groups gradually decreases with the increase of pile spacing. Conversely, under compressive action, the inclined helical pile-groups exert an influence on the soil in a larger extent, and the interaction effect among piles becomes more stable, without indicating obvious correlation between the extreme depth of vertical displacement of the soil at the center of the pile groups and the pile spacing and inclination angle. [Conclusion] The research results serve to provide certain research approaches and means for the construction of offshore wind power helical pile-group foundations in China, and hold certain reference significance for the dimensional design and bearing capacity evaluation of inclined helical pile-group foundations, demonstrating their value in scientific research and engineering applications.

Keywords

• offshore wind power
• inclined helical pile
• finite element analysis
• pile-group effect
• bearing characteristics