Abstract: According to measured results of in-situ static load test, static cone penetration test(CPT), heavy dynamic penetration test(DPT), and indoor soil test, we analyze three mechanical parameters of composite foundation of ram-compaction gravel pile, namely pile-soil stress ratio, bearing capacity, and soil’s compacted effect with piles. We take the construction of ram-compaction gravel pile in the 14th bid of South-to-North Water Transfer Project, located in Handan, Hebei province, as an example. Results show that, pile-soil stress ratio of composite foundation of ram-compaction gravel pile with expanding head is bigger than that of normal gravel pile, which is from 4.2 to 7.4; pile-soil stress ratio first increases and then decreases with the increase of load, and gradually tends to be stable, and the ratio increases with the pile length; then, the gravel pile’s curve of load vs. settlement (P-S curve) exhibits gradual change, without obvious inflection point or abrupt change point; furthermore, bearing capacity of composite foundation of ram-compaction gravel pile increases with pile length. According to the results of CPT and DPT, we find that the rammed gravel pile can effectively improve the strength of soil among piles, and decrease uneven settlement of the foundation.

Key words: ram-compaction gravel pile with end expansion, bearing capacity of composite foundation, pile-soil stress ratio, in-situ test , heavy dynamic penetration test, static load test