Experiment Research And Model Analysis On Bearing Capacity Of Pile Foundation Of Skyscraper

Super-long and large diameter bored Piles are used frequently due to its superiority of high bearing capacity in recently years as development of skyscraper. Though a large number of Super-long And Large-diameter Bored Piles have been used, its load transfer mechanism is not distinct. Today's Design standard of pile was based on the experiment of short and middle- long pile, so it can not suit super-long and large diameter pile. The research of the thesis has important theoretical and practical value.First of all, based on many scholars at home and abroad's research, this thesis researched the development of high-rise building pile foundation and its current status, summarized the characteristics of super-long piles and improvement rule of pile foundation by post-grouting technology. At the same time, author point out the develop way for the pile foundation of skyscraper after studying on the theory of pile settlement at home and abroad; Secondly, author carry out a systemic experiment on test piles at Hebei Kaiyuan Global Center foundation project and the China International Trade Center PhaseⅢproject. And then, author use Drucker-Prager model in ANSYS to analyze the bearing capacity of sign pile according to the data of test piles from Hebei Kaiyuan Global center.Finally, the thesis discussed on optimal design of the super-long and large-diameter pile. The main conclusions and understanding of this thesis are as follows:Firstly, the author summarize the characteristic and trend of pile foundation of skycraper based on the research status and finished project practice at home and abroad:①the Q-S curve of super-long and large diameter bored pile show that there is not turning point before the load limitation.②For long piles, the piles should check the appropriate diameter in order to give full play to the role of pile length;③Compared with the short-pile, the ultimate bearing capacity of long pile needs to have a larger settlement, so long pile ultimate load should be in accordance with the settlement;④The super-long large-diameter bored pile significantly increased its load-bearing performance after grouting.Secondly, through practice of Hebei Kaiyuan Global Center project and China World Trade Center project phaseⅢ, the author raised the characteristics of load transfer of super-long pile as well as the law of settlement of pile:①axial force of pile decreased with depth and reduced at different speeds in different soil layer;②along with the increase of pile load, load transfers from the top to down, that is, the friction of the upper layers effects earlier than the lower part. The friction of the upper layers first to reach the limit, and transfers down gradually;③the friction of soil gradually increase with the pile load increasing;④side friction account for most part of bearing capacity in the test pile which have obvious friction pile characteristic;⑤Measure value of the side friction are large than the value which be recommended by standard and the value of end resistance is opposite.Thirdly, the results of simulative calculation by ANSYS show:①DP model can be used to simulate the single pile bearing capacity of super-long and large-diameter bored pile. Simulative results of axis pressure, settlement and displacement are consistent with the experiment.②pile groups bring settlement and stress with dish shape which is harmful to upper structure because of combined function between pile and cap. So, it should avoid or decrease to design pile groups when foundation design. Finally, the results of researched on optimum design of super-long and large-diameter pile foundation show:①The combined function overall analysis way is to be thought as the best way and developing trend to optimum design. Designer can carry out analysis on combine function among upper structure, foundation, pile and soil based on conceptual design.②For pile design, designer should make use of relevant geological data to estimate the limitation of side friction and end resistance of pile at first. And then,the designer can used the data of static test to optimize the parameter of pile.