Bridge Pile Foundation In Collapsible Loess Area Calculation Of Negative Friction Resistance And Control Technology

In recent,years,with the development of road engineering,railway engineering,construction engineering and other projects,the pile foundation become one of the most widely used type of foundation.As we know,collapsible loess widely distributed in the northwest of China.After flooding of collapsible loess especially self-weight collapsible loess,there will be bigger settlement,and some negative friction at the pile side.Negative friction can cause the pile settlement increased,support capacity decrease and so on.Because of these,we must consider the impact of negative friction when we design and construction of pile foundations on collapsible loess.Firstly,We put the negative friction calculate into four parts:the soil of pile side and pile tip both in elastic stage,the soil of pile side in elastic stage while the soil of pile tip in plastic stage,the soil of pile side in plastic stage while the soil of pile tip in elastic stage,the soil of pile side and pile tip both in plastic stage.and then this paper derive the formulas of negative friction caculation on the four cases by Load-Transfer-Method.Second,We got the pile friction value and changing range of the loess area where the bridge would construct by water immersion test.and using the derived formulas and the specification formulas of China specifications calculated the negative friction of the loess.Then the calculated results and the test results were compared,and we gave the suggestions:Engineering project can use test results and the formulas we got based on Load-Transfer-Method to predict negative friction.At last,we summarized the current control methods on negative friction engineering.According to the characteristics of the actual project,we propose solution:sand pile and preloading method were used on transitional sections between abutment and subgrade,Pile bottom and lateral post-pressure grouting technology were used in large-scale bridge section.The applications of the project proved that the program can avoid self-wieght collapsible loess region suffered the impact of negative friction.The method could be used by similar projects.