Analyse On Settlement Characters Of Rigid-Flexible Piles Composite Foundation In Passenge Dedicated Lines

With the economic growth and the expansion of infrastructure construction, the technology of ground improvement has developed rapidly. There many new types of foundation have been put into desion and construction, the composite foundation with long-short-piles is one of them, it is largerly used in deep-thick soft soil areas. It breaks the traditional way of thinking that using single materal or single type to treat ground, but using various patterns to treat ground. Each component carries out its excellent function to achieve and optimize composite foundation's function. In this paper, for studying the behavious of multi-piles foundation and further improving the theory of the multi-piles composite foundation, theoretical method, field test and FEM were taken to solve the problem. The main contents can be summarized as follows:1. The general developing situation and basic theory of composite foundation are summarized in this peper, the creation of the long-short pile composite foundation; study the research production in long-short pile composite foundation is specially introduced. On the basis of synthesis analysis, it is the model and methods of settlement that have been proposed, and it is convenient that it been put into practice.2. Combining field tests of cement-soil deep mixing pile (be short for MIP) and cement fly-ash gravel pile (be short for CFG) composite foundation under embankment in high-speed railway. A variety of field data is analysised for studying the settlement deformation laws of the embankment body, reinforcement area and the below area. A conclusion was obtained that the settlement of composite foundation has completed about 75% of the total settlement at the end of load, the settlement of reinforcement area accounted for a small proportion of the total settlement; settlement of under straum accounts most of the total settlement.3. Numerrical simulation are carried out on settling character of long-short pile composite foundation by using the finite element method (FEM) software of plaxis. It proves to be correct and rational on basis of comparing with the field data. on the basis, the rules of the settlement, the vertical displacement of embankment and horizontal displacement of that are obtained. The settlement of pile-board structure and column-net structure are compared, and it shows that pile-board structure is more better to control differential settlement than that structure. The pile settlement of two structure is little different, however, the reinforced soil between of piles is very different.