Based on the actual project of northeast Second Ring Interchange of Xi’ an and through immersion test of soil layer and pile load test

this paper studies the side friction of pile foundation in collapsible loess layers

the tip resistance effect

the value selection of negative friction of pile foundation and the change of soil settlement around the pile.And it analyzes the experimental results to guide this project for pile foundation design.After summarizing several results of domestic engineering tests

the paper gives reasonable and scientific methods to select the value of negative friction in collapsible loess layer and also provides some factors which

should be considered.It analyzes the factors that influence the value of negative friction and that cause differences in settlement of soil around the pile.The result show that;（1） the side friction distribution around the pile is about 3

9

m

and its value is -2.0～-5.0 kPa.（2） the side friction value around the pile is related to piles length and geological environment

also to the settlement of collapsible loess and soil cohesion.This paper suggests that the collapsible loess has no influence on the bearing capacity if the collapsible loess layer is within 5 m and the pile lengths are greater than 20 m.This paper can provide references and practical experience for the future study of settlement of collapsible loess layers and the value of negative friction for pile foundation.