| With the construction of a large number of high-speed railway and passenger dedicated line, the requirements of railway line smoothness and stiffness are more stringent, so that in order to meet the requirements of high-speed railway construction and security operation, it is necessary to control the settlement of railway line strictly, especially to the bridge and culvert foundation, as a result, the differential settlement will be harm to high-speed train running. At present, the site pile test and measured settlement data of deep soft soil area super-long pile groups foundation are not enough, therefore, the comprehensive understanding of the settlement characteristics are restricted.In this thesis, base on the in-situ monitoring construction process at the Huangdu bridge section of Yunzaobang Extra-long bridge and the Suzhou aerial railway station of Beijing-Shanghai High Speed Railway, the settlement characteristics and mechanism of super-long bridge pile group foundation in deep soft soil region were studied, by using combination methods of on-site test, model test and finite element numerical simulation. First of all, the article elaborated the research progress and overalled the theoretical research level of pile foundation settlement at home and abroad, introduced the work traits of the settlement of pile groups, and summed up the settlement computational methods of pile groups are widely used at the domestic and international, also, their hypothetical conditions, the scope of application and their advantages and shortcomings were summarized and compared, so as to select the appropriate method of calculation conveniently. After that, the paper had detailedly analyzed the distribution of axial force in piles, lateral friction resistance of piles, additional stress and pore water pressure of foundation bottom, and the characteristic of load-settlement curve of super-pile group foundation at the vertical load axial force and the action of lateral friction resistance and the side friction resistance in piles. From the field test, model test and three-dimensional numerical simulation by using finite element software-ABAQUS, the finite element analysis results are in good accord with the experimental laws. By the experiments and the finite element analysis, some conclusions are obtained mainly as follows:(1)Under external loads, the axial force in piles decreases as the depth increase, while the lateral friction resistance of piles gradually plays a role from top to bottom along the piles, and act as non-linear distribution, arrive at the peak value within a certain range from the top of piles plane, then gradually reduced and maintained at a certain value.(2)At the bottom of pile cap, the additional stress and excess pore water pressure in the soil are gradually decreasing with depth increase, of which the values reduce near zero within a certain depth under the cap piles.(3)After the upper load apply on the pile groups, foundation settlement mainly includes two processes of immediate settlement and consolidation settlement. The maximum deformation occurs at the center position of foundation, the surrounding soil settlement is slightly smaller, and the soft soil layer within a certain range below the pile tip plane also has a little settlement. Meanwhile, the article detailedly analysis of the settlement characteristics of group pile foundation in soft soil area by changing influence factors were obtained, such as the number of piles, pile spacing, pile lengths, and pile diameter etc.(4)On the basis of field settlement observation data, forecasting of pile groups foundation settlement by using gray system theory is adopted, which could provide adequate data for the design and construction of high-speed railway.Above all, according to research results of the thesis, some correlative pile groups foundation settlement construct control measures are put forward, which could provide a certain reference value for construction of similar high-speed railway bridge's pile foundation in China. |
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