Variable Rigidity Design Method Of Rigid Pile Composite Foundation

With the application of the composite foundation in Civil Engineering Construction, although theoretical research and engineering practice has made great progress, theoretical research is still seriously lagging behind in engineering practice. In terms of settlement, although there have been some calculation or estimation methods, and in engineering practice played a good role in guiding, the existing theory almost all has different flaws and difficulties. Study on controlled-settlement desigin is also very few. People still design composite foundation by using conservative experience, this makes more or less unnecessary waste. Therefore, the depth research on theoretical calculation of settlement and controlled-settlement design is of great significance. In view of this, the thesis makes the following:(1) Based on the study of the rigid pile composite foundation settlement calculations, the new method , useing the Geddes and Mindlin solutions with the characteristic of considering the theory of load transmission,the distribution form of the skin friction of pile to calculate the settlement of composite foundation, is presented. The calculation for a project problem shows that the calculation results have good agreement with the project test results.(2) Based on the study of the interaction principle among raft,cushion and composite foundation, the thesis makes eight variable rigidity models by analyzing the way of variable rigidity design of composite foundation. By FLAC-3D geotechnical engineering numerical analysis software, we analyse the settlement,soil reaction force,pile top vertical reaction force and the raft's inner force, discuss the effect of variable rigidity design by changing the length,space and diameter of pile. Research shows that: The settlement of raft foundation was "butterfly" distribution. With the increase of load , the differetial settlement increase in first and then decrease. The model of combining the change of length with space of the pile will improve the state of the raft's inner force, decrease the raft moment, this is the best model of variable rigidity design.