Study On Negative Skin Friction Of Pile In Loess Collapsible And Its Influencing Factors

With the large-scale development of the western in China, the western region entered a new era of civil building, the construction of various infrastructure projects is rising rapidly, In order to meet the requirements of the seismic bearing capacity and high-rise building foundations, or settlement control for some of the building demanding requirements, pile increasingly being applied to the foundation treatment in the western region. However, the use of pile foundation in the western region, the western region will have to consider the unique geological conditions------ very large and deep collapsible loess. Many engineering examples show that after pile loess region in soaking, it will lead to dramatic additional settlement and greatly resistance in the axial force, because of the increased negative friction of the pile, in order to the safety of project, stable foundation laid a security risk. Engineering problems caused by collapsible loess has caused attention of academic and engineering.Therefore, the research of collapsible loess’ s formation mechanism and the impact of negative friction negative friction factor, for the improvement of the pile settlement calculation theory, and promote the pile foundation design has important theoretical and practical significance.The research attempted on the basis of previous studies,in loess region soaking pile load tests as the measure,on the pile bearing capacity, lateral friction, changes in the law and the neutral point, and to study the mechanism of the additional settlement of the pile,Combined with FLAC3 D field immersion simulated load test, and confirm with the experimental results. And at the same time study the various factors on the negative skin friction piles and additional settlement. Specific research carried out the following three areas:1. The results of the field test of immersion were analyzed, obtained collapsible loess-site venues bottom boundary, and intuitive got "No flooding" and "after immersion in water" and "pre-wet" conditions and "Wet " and other different conditions related to the pile settlement rule.2. The use of the sliding micrometer technology has been loaded pile displacement and deformation of soaking in the pile, the use of theoretical calculations obtained axial force and lateral friction, And draw additional settlement pile lateral friction graph changes with depth, Resulting in a variation on the development of both tests, and analyzes the mechanism of additional settlement of the pile.3. Using the FLAC3 D, by the method of strength reduction to simulate the experimental procedure. Analyzes the impact of various factors on the negative skin friction piles and additional settlement, Use graphics software, and data export functions, the law has been developed and additional settlement pile of negative friction. Theoretical analysis of the results were validated and supplemented.