Analysis Of CFG Pile-Raft Composite Foundation Settlement Under Hihg Embankment And Optimum Design

To insure high-speed and stable of trains operation, especially in soft ground circumstances, economic measures should be taken to deal with the soft ground so that the residual settlement will meet the relevant norms. A field test of soft soil CFG pile-raft composite foundation is conducted. CFG piles, the reinforced soil between the piles, underlying stratum, gravel cushion on top of the piles with a thickness of 15cm, reinforced concrete plate of 50cm, embankment filled with A or B fillers and pre-consolidation soil consist the on-site test system. The collected data were analyzed and a prediction was made, to infer the low of CFG pile-raft composite ground settlement under pre-consolidation soil. And the final settlement of the system can be obtained by hyperbolic curve, which can decide the prepress term and when to unload and when to lay tracks.The article structure is carried out as follows:The first chapter introduces the background of the article and innovation included in the thesis; and focuses on CFG composite ground theoretical basis, as well as methods commonly used as calculating composite ground settlement nowadays at home. The preconditions that methods can be applicable and some shortages are evaluated; aimed at high speed railway foundation improvement technology, the author refers to some calculation and analysis method. Chapter II gives a detailed description of on-site tests. Researches were carried on the settlement and settlement rate of CFG piles, the reinforced soil between the piles, the underlying stratum, the embankment body in different stages. A conclusion was obtained that settlement of reinforced part took a very short time to complete, and it accounted for a small proportion of the total settlement; settlement of underlying stratum accounts most of the total settlement; embankment filled with A, B group filler, according to the requirements of norms, the final settlement of the embankment can be 0.15 percent of its height; Chapter III arranges a finite element analysis, using Plaxis 2D to simulate CFG pile raft structure simplified as 2D. A comparison is made among the results of embankment overloading for 182 days by FEM, measured results and predicted by hyperbolic curve. We can see that the error between finite element simulation results and measured is less than 1%, which meets the practical requirements of geotechnical project. In the end, an optimum design is made to the available plan of the test .A calculation is carried out changing the pile intervals and the height of the concrete plate ,and a conclusion is drawn that the pile interval can be enlarged to 2.1m and the concrete plate height can be decreased to 0.4m.