Statistical Analysis and Proposal on Pile Negative Friction in Collapsible Loess Areas
YE Chao-liang, LIANG Kai-fang, WANG Xiang-yang
(1. Shijiazhuang Tiedao University, Shijiazhuang, Hebei 050043, China; 2. China Railway First Survey and Design Institute Group Co. Ltd, Xi′an, Shaanxi 710043, China)
Abstract：Abstract：Research purposes： Giving reasonable value of pile negative friction and the depth of the neutral point is a difficult problem which researchers and designers concern most when designing pile foundations in collapsible loess areas. On the basis of analysis of the influence factor of the pile negative friction and the neutral point depth in collapsible loess areas, this paper collects more than 30 research findings of domestic field immersion test to make summary and statistical analysis of the pile negative friction and the neutral point depth in collapsible loess areas. Research conclusions： (1) By making statistical analysis of massive measured data, it makes clear the upper and lower limit of pile negative friction and the neutral point depth. (2) When pile top elevations are lower than -5 m, the collapsible soil depth of the soil surrounding the pile is less than 6 m and the collapsible class is lower than Ⅱ, the soil surrounding the pile does not apply negative friction to piles. (3) In practical engineering, there is always large load applied on the pile top and collapsible probability and level is far less adequate than field injection, which all make the depth of the neutral point move up in practice and this paper suggests that taking value of the neutral point depth in 0.5～0.7. (4) By making statistical analysis of massive measured data, it suggests that taking negative friction value in 15～35 kPa is factual when design piles in deep collapsible loess areas and there should be more in-situ tests of pile foundation negative friction characters in loess areas. By combing research achievements, this paper can provide the basis for the pile foundation design in the deep collapsible loess area.
2018, Vol. 35 
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