Research On Vertical Bearing Behavior And Deformed Mechanism Of Supper-long Hole Bored Pile In Xi'an

With the quick development of urban construction and increase of super high buildings of Xi' an city, the super-longhole bored pile has been presented its unique fascination and broad application field in the base processing, at the same time more strict design plan was needed in the pile foundation design. Because of the complex of pile-soil interaction, the study on this subject is far from demand so far, and the theory lagged behind the engineering practice.Reviewing the calculating theory of various single pile under the vertical static loading, and analyzing the vertical static loading test results of the super-longhole bored piles of four significant buildings in Xi' an, the author analyzes the load transfer mechanism of the super-longhole bored pile in loess. The Q^s curves of the super-longhole bored piles is presented as gentle style.Using the stress test results with sliding micrometer, the author analyze the varied feature of pile shaft compression, the distribution of shaft axial force, the impact of lateral friction resistance of the super-longhole pile and the influence factors; The complex coefficient in the simplified formula used to predict the settlement is checked and revised. The research result shows that the lateral friction resistances force works out of phase in the different soil layers. It is also found that the shaft axial force under the vertical load is decreased with the deep of pile, and the bottom resistance under the top load is less than 15%, so it is considered that the super-longhole present the friction pile type in the loess foundation.Based on the tested and calculated lateral friction resistance, bottom resistance and pile-soil displacement, the model of load transmission function is deduced, the load transmission function of lateral friction resistance is hyperbola model, and the load transmission function of bottom resistance is bilinear rigid model.On the research of above mentioned, in order to analyze the correlation between ultimate lateral friction resistance and soil property indexes, such as water content(w), unit weight( γ), liquidity index(I_L), void ratio(e) and coefficient of compressibility(a_1-2), statistical analysis of the in-situ test results of 14 sites has been completed. The regression equations with multi-analysis of Liquidity index(I_L) and Void ratio(e) and ultimate lateral friction is achieved, and the quantitative analysis model of ultimate lateral friction is built, the correlation coefficient is high.In addition, According to the stratum constitute of the same sized pile, boundary condition, the numerical simulation physical model of single pile is founded. Through determining the appropriate parameters, the transferring law of axial force and pile-soil interaction are simulated. The simulated results and the test results are compared.