A new driven cast-in-place Y pile was developed according to the innovative design concept of Y pile and the traditional construction technology of driven cast-in-place pile in China. In this paper the pile-soil stress ratio was calculated based on the hypothesis that the pile body was modeled as an equivalent constant section elastic bar. The influence factors and variation of the pile-soil stress were analyzed. Then the theoretical results were compared with the field data obtained from a ground improvement project for an expressway bridge abutment using driven cast-in-place Y piles. According to the field static loading test and theoretical analysis, the driven cast-in-place Y pile can improve the bearing capacity significantly with the same engineering quantity. It can be indicated that Y pile is either a friction-based friction pile or end-support friction pile and has a great bearing capacity. Besides the Y pile composite foundation has better bearing characteristics while the foundation settlement and post-construction settlement of embankment are substantially reduced. The results from this study can provide reference for the future design of similar composite foundation.
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