| At present, orderly, rational, comprehensive and efficient exploitation and utilization of existing building underground space resource, that becomes one of the most effective way to expand infrastructure capacity reasonably, improve the urban comprehensive ability of preventing disaster, save the land resources. Before building basement below existing buildings, we need to use the original pile foundation or add new pile foundation for the upper structure load, in order to excavate the earthwork under buildings. As pile soil gradually reduce, pile foundation exposure, it not only affects the pile lateral friction resistance, but also causes a decline in pile buckling stability obviously. Therefore, carrying out the research on the pile foundation buckling stability of the building under the condition of excavation of research is particularly important.Based on illusion embedded point method, this paper puts forward the formula of calculation length of compressed pile foundation under the three states that the part of pile depth in soil is embedded, un-embedded and half-embedded. In order to verify the reliability of the formula by using numerical analysis and experimental study on the method:first, with ANSYS this article analysis specific excavation depth of concrete piles with the increase of soil depth, the stability coefficient of variation; Secondly, the compression bearing capacity and bucking stability of steel pipe is tested in model box by pry bar loading devise, which get the limit load of steel pipe under a certain excavation depth and stability with the increase of soil depth change rule. Comparing the results of numerical analysis and experimental results with the calculated value of illusion embedded point method.The results show that excavation at a certain depth, with increase of buried depth, the stability coefficient of pile in soft soil decreased gradually, but in hard soil increases slightly. They all tend to be the constant value, when that buried depth reaches its critical embedded depth of solid, which is close to the 4T value that puts forward from the code for pile foundation of port engineering. The illusion embedded solid point method give fully consideration to the restriction of pile and the pile itself and the pile of soil parameters on the stability of pile foundation effect, especially the buried depth of piles on the calculated length coefficient and the equivalent pile length correction, satisfying the state of actual compressed pile. The numerical analysis method and the model test confirm the reliability of the calculation formula of the illusion embedded solid point method which is proposed in this paper, and provide the theoretical foundation for the development and utilization of the underground space.In view of the characteristic of the actual engineering that the pile length is invariable, the excavation depth of the pile is increased, the stability of the pile is simulated by using ANSYS finite element software. The results show that the stability coefficient of the pile foundation is smaller when the excavation depth is lower, the pile top constraint is weaker, the pile’s soil level reaction coefficient is smaller, the pile diameter is smaller. Under the same excavation depth, the pile cap and the pile body are provided with the horizontal support, and the stability of the pile foundation is improved by 2～3 times. When the vertical load is constant, increasing the horizontal load, pile foundation stability decreased obviously, and with the increase of excavation depth, the fall of stability increased, but the level of support can effectively resist horizontal load.When the eccentricity increases, the stability coefficient of pile foundation under the same excavation depth is obviously decreased. The numerical analysis results are compared with the calculated values of the illusion embedded point method, the two trends are consistent, and the numerical difference is not large. |
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