Abstract：A new driven cast-in-place Y pile，developed according to the innovative design concept of Y pile and the traditional construction technology of driven cast-in-place pile in China，was introduced in this paper. The newly developed piles were used in a ground improvement project for an expressway bridgehead. Based on the theoretical calculation and static load test results，the longitudinal surface area of a Y pile is about 50% more than that of a circular pile for a given cross-sectional area，from which its side friction and bearing capacity is substantially enhanced. The Y pile is either a friction pile or end bearing friction pile from its working mechanism. Based on the field monitoring results and static load test results，the pile-soil stress ratio，surface settlement，lateral deformation of the driven cast-in-place Y pile composite foundation were discussed. The Y pile composite foundation has better bearing characteristics while the foundation settlement and post-construction settlement of embankment are substantially reduced. From the technical and economical point of view，it has certain advantages over other composite foundation on reliable construction quality，significant reinforcement effect and economical rationality. It can be applied to other projects with similar geological conditions.
