Investigation into pullout characteristics of root piles within coral sand foundations at varied relative compaction

Abstract

Root piles exhibit favorable bearing characteristics, rendering them suitable for the foundation of offshore wind power facilities to withstand uplift loads. This study compared the uplift load bearing advantages of root piles to those of equal diameter piles in coral sand foundations. Additionally, it analyzed the effects of relative foundation compaction on the uplift load bearing characteristics of root piles. The tests involved comparing root piles and equal diameter piles in coral sand foundations with relative foundation compaction levels of 0.5, 0.6, 0.7, and 0.8. The results indicate that root piles possess a 62.5% higher pullout capacity than equal diameter piles, with only a 10.7% increase in uplift displacement. As relative compaction increases, the pullout ultimate capacity of root piles initially rises rapidly and then levels off, while the corresponding uplift displacement experiences a sharp decline followed by a relatively stable state. With the increase of relative compaction, the location of the maximum attenuation of axial force and the maximum lateral friction resistance in the root region started to move deeper only under larger loads. Both the implementation of root piles and an increase in relative compaction greatly enhance the pile foundation’s ability to resist pullout forces and control deformation.