Abstract: Based on a project in Lanzhou New District, this paper conducted a comparative study on the strengthening effect of compacted pile composite foundation with different pile types, such as plain soil compacted pile, SDDC compacted pile, and two kinds of compacted pile combination in collapsible loess area through a large number of tests to evaluate the bearing capacity of compacted pile composite foundation, the compaction coefficient of pile body soil, the compaction coefficient of soil between piles, and the collapsibility of loess. The results show that all three pile types of compacted piles can effectively improve the bearing capacity of the foundation and improve the collapsibility of loess. Plain soil compaction pile has limited ability to improve the bearing capacity of the foundation, with the soil compaction degree between piles greatly affected by the particle size of backfill soil, resulting in uneven densification. SDDC compaction pile has a better effect on improving foundation bearing capacity and settlement control than plain soil compaction pile.

Key words: collapsible loess, composite foundation, foundation treatment, SDDC compaction pile, plain soil compaction pile