Count And Study On The Collapsible And Negative Friction Of Pile In Collapsible Loess Region

There have large area of collapsible loess in the west of our country. More skyscrapers and important infrastructures are being built with development, piles foundation is used extensively in this area. It will produce heavy negative friction when the ground soaked, and it will cause different destruction, this problem has become a hot problem to be solved urgentlyThis article established a negative friction transferring model according to its mechanism, and analyzed the parameter's value, and indicated friction is related to the development of soil strength. The model accord with the hardening model of two lines in saturated soil and accord with the soften model of three lines in unsaturated soil.Through analysis to the testing data of predecessors, this article got the expression of equivalent moistening stress which can be used in different loess regions based on "loading immersing equivalent " principle, and got the expression of the negative friction with the consideration of time based on elastic-plastic theory, and got the expression of the collapsible and negative friction and the neutral point when T→∞,and confirmed its feasibility through the contrasting to the actual testing data in the end.At last, the collapsible and negative friction of single pile and group pile was analyzed through the finite element software ADINA. The influence scope is about 30 times of pile diameter. Neutral point and negative friction are analyzed in two conditions of immersing after loaded and loading after immersed. The analysis indicates the spacing is suitable when controlled in 4 times of pile diameter in collapsible loess region. And the methods to prevent and control the collapsible and negative friction are discussed.