Experimental study on the lateral resistance lifting effect of HSCA expansion piles on coral sand foundation

The bearing performance of pile foundations in marine environment island and reef engineering construction is often closely related to the fragmentation characteristics of coral sand. It is of great significance to clarify the impact of coral sand particle fragmentation on the bearing capacity of pile foundations. Based on this, a series of HSCA expansion pile model tests and field tests were conducted to explore the effects of the normal stress of the expansion pile and the compactness of the coral sand on the improvement of pile side friction resistance. The research results show that: (1) incorporating HSCA high-strength expansion agent can significantly improve the normal stress on the pile side and the compactness of coral sand around the pile, thereby greatly improving the pile side friction resistance and overall pile bearing capacity. When the expansion agent dosage reaches 15%, the ultimate lateral resistance of the expansion section of the pile increases by 69.7%, and the ultimate bearing capacity of the entire pile increases by 38.5%. (2) Considering the cumulative stress loss effect due to particle breakage, a stress transfer model for the expansion of coral sand on the side of expansion piles considering particle breakage is proposed. Verification analysis demonstrates that the model accurately reflects the transfer law of expansion stress in coral sand. (3) The expansion pile significantly improves the compactness of coral sand on the pile side. The self-expansion of the pile body effectively fills the shrinkage space in coral sand caused by particle breakage, thereby enhancing the bearing capacity of the coral sand foundation around the pile. (4) A prediction model for lateral friction resistance of expansion piles in coral sand foundations was established and its engineering applicability was verified through field experiments. The findings of this research can serve as a reference for the construction design of expansion piles in coral sand foundations.