Abstract: In the research on negative skin friction on pile, the pile-soil displacement is the key point concerned. As a mature flow test technique, the particle image velocimetry(PIV) is gradually used in the field of geotechnical tests. By applying PIV technology in the model test of negative skin friction on pile, some defects of traditional displacement measuring technique, such as cannot obtain displacement field, will be improved. Aiming at the characteristics of test, a testing box was designed which included steel plates and organic glass plate. The soil surface load was simulated by jack and load board. Settlement of each soil layer, settlement of pile and axial force were measured in the test; and the displacement field around the pile base was measured by PIV technology under various stages of heaped loads. The test results show that the settlement measured by PIV technology is consistent with the settlement measured by traditional technology. The results of PIV analysis can intuitively reflect the additional settlement caused by the negative skin friction on pile. In addition, influence scope of soil displacement caused by the settlement of pile is analyzed. The analysis results show that the vertical influence scope is about 1.75D (Disdiameter) and the horizontal influence scope is no more than 1 D. At last, a summary is made about the application of PIV technology to this model test, and some issues for future study are put forward.

Key words: particle image velocimetry(PIV), pile, negative skin friction, model test, neutral point, axial force, displacement