Abstract: Based on full scale in-situ immersion tests of SDS piles, the results showed that as the compacting effect of SDS piles, the negative friction resistance of the single pile would be increased, informally called as "factting pile effect". Through research on change laws of collapsible coefficients for soil arround SDS piles, conclusions could obtain that arranging reasonable spacing between plies could eliminate the soil collapsibility between piles and improve bearing capacity of single piles. The SDS pile would be a kind effective improvment method for foundation design of high or superhigh buildings in collapsible loess zones.