Theoretical Study On Settlement And Deformation Of Pile Groups Of Beijing-Shanghai Express Railway

The Beijing-Shanghai high-speed railway is the main passenger traffic line connecting north and south China. It is also the first high-speed rail of world’s advanced level in China. The Beijing-Shanghai high-speed railway is approximately1318km long. Group pile foundation becomes the primary form of foundations when the railway goes through areas with complicated geological conditions such as soft soil, lakes and so on. In order to control the settlement of group pile foundation, it is necessary to study the mechanism of pile-soil interaction.In this paper, based on group pile foundations of Beijing-Shanghai high-speed railway, pile-soil interaction problem in various situations were discussed using theoretical analysis and numerical simulation. The main contents and conclusions include following aspects:(1) Considering the diffusion effect of shear stress around group piles, ignoring the influence on settlement caused by the compressive deformation of soil between piles, assuming that the bottom surface of pile foundation is flush with the pile end, and only considering the vertical seepage of soil, analytic solution for compressive deformation of pile end stratum was deduced using a method similar to equivalent pier method. Analysis shows that, the results of this method agree with the results in existing literature when the top surface of stratum is completely permeable.(2) Using Berg rheological model and Biot’s consolidation theory, soil consolidation-rheological model was established. Time effect of stress and deformation of group pile foundation under consolidation-rheological coupling force were simulated by FLAC3D. The results show that the calculation results of soil settlement increase if creep effect is considered, especially for the pile tip stratum. Simultaneously, the settlement rules of group pile foundation are revealed better and the settlement prediction is more accurate.(3) Through analysis of the stress and deformation characteristics of pile foundation bearing cofferdam loads using FLAC3D, the variation of soil settlement, pile foundation settlement, pile axial force and frictional resistance with time and depth are obtained.(4) Simulations are conducted respectively on adjacent group pile foundations built in different construction sequences. Results show that, settlement can be well controlled if adjacent group pile foundations are constructed at the same time.