Study On Characteristics Of Bearing And Deformation Of Composite Foundation For High-speed Railway Cap-pile And Raft-pile CFG Pile

The composite foundation of pile cap and pile raft with CFG piles in consolidating softclay foundation technology has been widely used in the construction of the high-speedrailway. At present, the research on transferring rules and mechanisms of the load in thecomposite foundation of pile cap and pile raft with CFG piles has mainly been focused onrigid foundation conditions, and a relatively complete system of theory and calculationmethods has been established. In the flexible foundations, however，the research on the rulesof load transfer and working characteristics of it is not perfect enough. It is unable to form asystemic theory to guide the practical application. Consequently for the high-speed railwayunder embankment load, the related research of bearing capacity and deformationcharacteristics of composite foundation with CFG piles is necessary. The present study firstlyhas carried on the test research of the composite foundation model of pile cap and pile raftwith CFG piles, and then the numerical analysis method is applied to calculate the bearingcapacity and deformation characteristics of CFG pile composite foundation. Finally, the rulesof model test and numerical simulation are compared. In this paper, the main work is asfollows:(1) Under the action of flexible load on embankment, the current status of research anddevelopment in three areas, respectively, in theoretical research, numerical simulation andexperimental study of pile cap and pile raft composite foundation with CFG piles issummarized. Secondly, the analysis of the problems which exists in the research of pile capand pile raft composite foundation with CFG piles, provides a analysis precondition andreference for this article.(2) The basic concepts of CFG pile composite foundation and the differences betweenpile cap and pile raft composite foundation with CFG piles and CFG pile compositefoundation are briefly introduced. Then, the function mechanism and the load-sharing rules ofthe pile cap and pile raft composite foundation with CFG piles under the embankment loadare analyzed, which lays a theoretical foundation for the laboratory model test and numericalanalysis.(3) Based on the embankment structure type of pile cap and pile raft compositefoundation with CFG piles in the construction of high-speed railway, the implementation plan of laboratory model test is designed combining similarity theory. The experimental study hascarried on the reinforcement effect of pile cap and pile raft composite foundation with CFGpiles in flexible load on embankment. The sedimentation, pile-soil stress ratio and the stressdistribution of pile body in condition of two structure kinds of composite foundations insupporting type and suspension type are separately tested and compared with the changingrules of load.(4) The numerical simulation study is used in several different working conditions ofcomposite foundation with CFG piles using software of finite element analysis MIDAS/GTS.The load and settlement characteristics of four kinds of composite foundations in the processof stratified filling embankment construction are calculated and analyzed. And the results arecompared with the results of laboratory model test, validating the correctness of the finiteelement model.Through the study of this paper, there is a systematic cognition about the characteristicsof bearing and deformation of pile cap and pile raft composite foundation with CFG piles bytheoretical analysis and laboratory model experiment. It establishes certain basis forcontinuous research and provides relevant reference for practical application.