Abstract: The dragload of tapered pile can be reduced by inverted tapered angle. However, the researches focused on the relationship between tapered angle and neutral point position are relatively little. In order to analyze the pile-soil interaction mechanism of tapered pile and equal section pile under surcharge load, based on transparent soil material and particle image velocimetry(PIV) technology, model test on neutral point position of tapered pile and equal section pile are comparatively carried out. The pile and layered soil settlement under different surcharge loads are non-intrusively measured. The pile-soil relative displacement and neutral point position versus surcharge loads are analyzed and discussed. The results show that transparent soil material is technically feasible for studying the neutral point position of piles problems. The results also show that the neutral point position of tapered pile and equal section pile decrease with surcharge loads increasing in this model test condition.

Key words: tapered pile, negative skin friction, neutral point, model test, transparent soil