Abstract: Load on pile top is acted after the settlement of soil surrounding the pile in bearing capacity test of piles in collapsible loess, and it is acted before the settlement of soil on general working condition of pile foundation. Different mechanisms of pile-soil interaction between such two loading sequences are simply analysed. Finite element method is used to calculate the differences. Analysis results show that settlement of pile increases, neutral point goes down and dragload induced by negative skin friction reduces as the load on pile top increases in both loading sequences. It also shows that comparing with load on pile top acted before in general working condition, loading sequence of bearing capacity test in collapsible loess would make the neutral point position in pile lower, settlement of pile smaller and the dragload in pile smaller. The differences of neutral point position, settlement and dragload in the two loading sequences increase gradually as working load increases. At every stage in both loading sequences, there exists small differences on distribution and development of skin friction along the piles. This will cause the testing result of bearing capacity of piles relatively unsafe in collapsible loess zone

Key words: collapsible loess, pile, bearing capacity test, negative skin friction, loading sequence