Study On The Mechanics Properties Of The Strengthen System And The Design Calculation Of High-Speed Railway Pile-Raft Composite Foundation

The research means for high-speed railway pile-raft composite foundation are concentrated on experimental study, but lack of systematic and in depth researchs. The study of interaction method, which is a method for the design calculation of high-speed railway pile-raft composite foundation, is systematic, but the difficulty rise because of the cushion, and this method usually depends on finite element and computer techonology. The excessive hypothesis and approximate in common used elastic-foundation-beam(raft) method and simplified calculation method reduced the precision of the research result, and the difference between their results and measured value is often significant.The mechanics properties of the strengthen system-CFG pile,raft and cushion-are important contents of the working properties of high-speed railway pile-raft composite foundation. This paper firstly carried out a systematic and in depth research on the mechanics properties of the strengthen system by numerical analysis. The study suggested that the mechanics properties of the strengthen system vary significantly only in vertical direction of the route.This indicates that the space effect of the raft and pile foundation is not obvious along the railway.And with proper assumption,the usual practice in which subgrade is simplified to2-demention in the design can be also applied in the design calculation of high-speed railway pile-raft composite foundation.This paper next proposed a2-demention analytical method for the design calculation of high-speed railway pile-raft composite foundation,which is based on force method. The effect of the cushion is fully considered in this method. Internal force and deformation characters of the CFG pile-soil-cushion-raft system can be obtained through this method. The comparison with in-site and numerical analysis results verifies the rationality of this method.Based on the method,the paper analyzed major factors which influence the internal force and settlement of high-speed railway pile-raft composite foundation and their influence law in the end. The results showed that it’s reasonable to arrange CFG pile by "square, distance2.4m" mode, and that the optimal length of the CFG pile exists in high-speed railway pile-raft composite foundation.