Abstract: A new pile type, X-shaped cast-in-place concrete pile (XCC pile) was developed for coast or river soft soils treatment. XCC piles have many technical and economic advantages, such as large surface area, high shaft friction, conveniently construction, and high economic effects. But there were relative little studies focused on the pile-soil load transfer characteristics of XCC pile composite foundation. Based on a sewage treatment plant soft ground improvement engineering, field tests for the pile-soil load transfer of XCC pile composite foundation were carried out. The load-settlement, pile-soil load sharing, pile-soil stress ratio, and the distributions of axial force of pile shaft were measured. Then the pile-soil interaction and neutral plane of XCC pile under different conditions were analyzed. In order to do comparative analysis, the static load tests for circular pile which has the same concrete amount with that of XCC pile were carried out. The results show that, the neutral plane of XCC pile in composite foundation is mainly occurred in 0.2 times of pile depth. The maximum value of positive skin friction is about 140 % of those of negative skin friction. The pile-soil stress ratio of XCC pile in composite foundation is increased with the decreasing of pile spacing under the same pile length.

Key words: XCC pile, composite foundation, field test, pile-soil load transfer, pile-soil stress ratio, neutral plane