Abstract: The pile bottom sediments cannot be cleaned up completely during the construction process of drilling with pre-stressed concrete pile cased (DPC) piles, which may lead to the loss of bearing capacity of the pile. Model tests for DPC piles with consideration of the pile bottom sediment effect are carried out in this paper. The load-settlement curves of DPC piles with enlarged cement-soil pile end show slow-varying, while other tests of DPC piles with pile end sediments show sharply down. The influences of the sediment thickness and enlarged pile end on the vertical bearing characteristics are studied. Experimental results show that the pile end sediment has a certain impact on the vertical bearing capacity of the DPC pile, and its bearing capacity can be improved by around 22% after removing the sediments. Compared with the bored cast-in-place pile with a certain thickness of sediment, the sediment at the bottom of DPC piles has less effect on reducing the bearing capacity. Besides, DPC piles with expanded cement-soil pile end can increase the bearing capacity by 37% in approximation. The external load of the DPC piles with pile bottom sediments is generally borne by the pile side frictions for more than 90%, and the pile axial forces near the pile end become smaller with thicker sediments. In dense sand strata, the pile end resistance ratios of DPC piles are less than 15%. Both in-situ (pile length 15.5 m, pile length-diameter ratio 15.50) and indoor model test (pile length 1.0 m, pile length-diameter ratio 15.87) results show that DPC piles with pile bottom sediments are the type of end bearing friction piles. These research findings may provide a reference for further understanding the bearing characteristics of DPC piles.

Key words: model test, DPC pile, pile bottom sediment, pile foundation, bearing characteristics