Study On The Vertical Bearing Capacity Of Large-Diameter Bored Cast-in-Situ Long Pile

Based on a lot of in-situ measuring data in Changzhou viaduct road project(I), the working mechanism of the pile-soil system in large diameter bored cast-in-situ long pile under vertical load in Changzhou area is studied. Many aspects about the behavior of the lateral frictional resistance and tip resistance of pile are expounded in detail.The ranges of relative displacement of pile for some soil layers, with which the lateral frictional resistance can reach to limitation, are given by the analysis of pile 5-1#. It is proved that for soil layers with similar soil property, the deeper the buried depth is, the greater the required settlement is.The process-softening model is obviously presented as the load transfer function of soil layer (3) of pile shaft, which can be described as a combined model with hyperbola and two lines. And the load transfer functions of the other soil layers of pile shaft basically correspond to the hyperbola model. And the load transfer function of pile-tip corresponds to bilinear rigid model.On the basis of displacement-coordinating method, a particular method of the load transfer method, a corresponding program is compiled. The analysis of single pile using this program indicates that the method and the corresponding program have great practicability. In the case of same diameter, as long as the information of soil-layers and pile are given, it will be very easy to obtain the bearing behavior, also to predict the ultimate bearing capacity. In this way, a great deal of manpower, material resources and financial resources can be saved.Some conclusion about relation between pole-top load and settlement of the field is deduced by analyzing the Q₀～s₀ curves of thirteen testing piles in the project. The analysis reveals a fact that relevant design criterion is to be studied further, and presents a method forecasting the vertical bearing capacity of the single pile by the use of some a pile-top settlement. Meanwhile the Q₀～s₀ curves of static load testing data are simulated very well by Boltzmann mathematic model. The bearing capacity of 7 verified testing piles can be inferred by Boltzmann mathematic model according to pile-top settlement mentioned above. The results have practical value and provide a reference in the hereafter design.