High Speed Railway Ballastless Track Pile Raft Composite Foundation’s Reacting Force And Dynamic Response Of Foundation Bed

In the design of railway in the past, the research on stability of subgrade is mainly about the basic physico-mechanical properties, Statics properties and bearing capacity of the soil, but the research on dynamic performance of subgrade and the counter-force calculation and study which based on the former are relatively less. Compared to traditional track, high-speed railway have rather high standard on subgrade, fatigue strength properties of foundation, accumulated plastic deformation and dynamic stability, hence the dynamic stability and counter-force study under dynamic effect become an very important need to be solved soon.This paper based on ZhengJang testing section of Shanghai-nanjing intercity railway, through the field monitoring, finite element modeling and theoretical analysis, conducted the study on high speed railway ballastless track pile raft composite foundation’s counter-force and dynamic response of foundation bed.1、Conduct field test on the selected testing section of Shanghai-nanjing intercity railway, introduced the test section project summary, test scheme and the layout of earth pressure cell,etc.2、Pass the analysis of the selected testing section, get through the conclusions as follows:(1) As the embankment filling and overload preloading, the stress of pile top and pressure between the piles are all rising at diverse level, after unloading of the preloading soil, the pressure of each section towards stability.(2) Under Pile-Raft compostite foundation, The pile pressure and the earth pressure beteen them is diverse greatly, the shape of soil pressure is wave-shaped, which presents both sides big and middle small.(3) Under the same condition, the bearing capacity of the bottom of the raft pile performs better than geogrid network, but due to The margin effect on rigid foundation, the bearing capacity of each pile below the raft varies considerably, lead to a better performance of side piling over middle pile.(4) When the height of subgrade reclamation reached6meters, compared to gravel grouting pile composite foundation, CFG pile have better holding effect, and the use ratio of adjacent soil is higher.3、Finite element procedure Plaxis is used to analyze the dynamic reaction pattern of dynamic load of high speed railway, and also analyze the dynamic reaction features under various train load parameters (including the train axle load and velocity) and subgrade designing parameters (thickness and stiffness of surface-based bed, the thickness and stiffness of bed bottom).4、Combined with the dynamic reaction pattern, a revised model of diffusion angle method is employed to form the counter-force model of foundation, comared the calculation results of the aboved model and field test results, verified the the feasibility and effectiveness of this model.