Numerical Simulation Analysis Of Pile-plank And Lattice Beam Structure Composite Foundation Of High-speed Railway

Transporting passengers in the ways of high-speed, comfort and security are the main characteristics of high-speed railway, which require that the subgrade must have the advanced properties of high strength, high stiffness, longitudinal changes in uniform, long-term stability and not-easy deformation. For the subgrade, strength design is always focused on and strength is taken as the main control factor of the under-track system. At present, the strength is no longer a problem. Generally, the harmful deformation would reach too large before the strength is damaged, which is not allowed. Therefore, the deformation has become the main control factor of subgrade design of high-speed railway.Taking "subgrade design of Siping station stop paragraph of Shen-ha dedicated passenger line " as the basis project, based on the point of exploring new methods to treat the foundation of high-speed railway, this paper makes numerical simulation on the models of pile-plank structure and pile- lattice beam- geotechnical grille structure composite foundation with different combinations of the parameters by the use of nonlinear finite element software of MSC.MARC. In the calculation, the soil is considered as the elastic-plastic constitutive model, and the track plate, embankment and foundation are considered as a system on which the combined load is applied. According to the simulation results, the settlement deformation law and the stress-strain characteristics of each model are analyzed, and the main achievements are as follows:(1) According to the finite element numerical simulation analysis of pile-plank structure composite foundation, it could be obtained that 6 groups horizontal and 8 groups vertical combined structure model all satisfy the design requirements of settlement deformation and stress, and the stabilities of all models are very good. Considering the economic benefits, the pile-plank structure model of plank thickness being 0.4m, pile diameter being 1.0m, five piles in horizontal, vertical pile spacing being 7.0m is the best one to choose.(2) Through the analysis of finite element numerical simulation results, laying 3 or 4 layers of geotechnical grille in the pile- lattice beam- geotechnical grille composite structure could basically satisfies the design requirements. However, due to stress concentrates at the contact part of lattice beam and geotechnical grille, the stress beard by the grille is over its yield stress value, and the geotechnical grille may be pulled off possibly. Therefore, compared with the pile-plank structure, the stability of such a composite structure is a little relatively poor(3) By changing the property of cushion, it could be found that improving the strength of filling soil between piles and cushion can improve the stress state of grille and the stability of the whole structure, the pile- lattice beam- geotechnical grille composite structure is also feasible, and it also can reduce the layers of geotechnical grille.