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| Model Test of Pile Negative Friction for Different Pile - end Underlying Layers |
| MA Xue - ning，ZHANG Pei - yun，JIA Xi - cui，LI Shan – zhen |
| (Lanzhou Jiaotong University，Lanzhou，Gansu 730070，China) |
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Abstract Abstract ： Research purposes： The negative skin friction could produce dragloads on pile，which will cause the increase of displacement and the decrease of vertical compressive security levels，even results in pile destruction. To analyze the influence of different underlying layers ( loess and coarse sand) on displacement and negative skin friction， through model tests，this paper compared the difference of pile and pile - surrounding soil displacement，and the distribution of axial load for these two underlying layers， then clarified the change regularity of neutral point position and gave the suggestion value. Research conclusions ：( 1) The influence of underlying layers on pile - surrounding soil disj)lacement is smaller，while on pile displacement is bigger. Compared witli loess underlying layer，the neutral point position of coarse sand is deeper under the same surcharge loading level. ( 2 ) The axial force of these two underlying layers increases with the increase of load level. But tiie dragloads and pile - end reaction of coarse sand are bigger than loess. (3) The neutral point positions which are determined by pile - soil relative displacement and peak axial force are basically the same. (4) Considering the geological conditions in actual engineering，some appropriate measures should be taken in order to minimize pile negative friction and make full use of tiie bearing capacity of pile. (5) This paper suggests that tiie neutral point position of loess underlying layer ranges from 0. 51 to 0. 61 while coarse sand underlying layer ranges from 0. 61 to 0. 81. (6) These results can provide some references to decision and design of the neutral point under surcharge loading in the similar projects.
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Received: 21 July 2016
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2017, Vol. 34 
