Settlement Analysis Of Pile Group Foundation Of Bridge Under Vertical Loading

The high speed running of train needs smooth and stable foundation of track undersurface. It means that a high quality of stability for the settlement is needed for high-speed railway. It is that new design standards has been applied to the Jing-Jin dedicated passenger line, to ensure the train safety, stability and passenger comfort in tune with the design speed once open to traffic. Especially in bridges, the new design standards are stricter with settlement and post construction settlement of bridges pier. So, it is necessary to develop analytical technique based on reasonable theory and simplicity to calculate settlement and post-completion settlement. The research production may offer useful parameter and experience in design for the similarity.The paper is based on the Jing-Jin dedicated passenger line's traffic scientific research project " Testing study on foundation of bridges and culverts on soft ground ". In this thesis, the settlement of group-pile foundation high-speed railway on soft soil is studied both by finite element method and by gray theory.There are several main works of the ultimate settlement. Firstly, the thesis presents the development of calculating settlement of pile group foundation at present. Secondly, ultimate settlement of pile group foundation is calculated with the finite element analysis software package, PLAXIS 3D foundation. The result is compared with current criterion as well. Thirdly, the working rules of the ultimate settlement, the axial pressure, side friction and tip resistance of the pile, load ratio by cap and pier-subsoil average stress ratio which are influenced by many complicated factors, such as, properties of soil, load-level, spacing and length of piles, compressibility modulus of soil are analyzed and summarized.The settlement prediction of group-pile foundation is studied both by PLAXIS 3D foundation and gray theory. An analysis and computation on the basis of Biot's Consolidation Theory by using the finite element method in the relationship between settlement and time varying and load is compared with actual data. The conclusion shows that the two settlements agree with each other very much, so, the method introduced is rational and possible. Furthermore, gray theory is used to predict the settlement of high-speed railway. The conclusion shows that the prediction the value is precise gained based on gray theory. Based on the model GM(1,1 ),the unequal time-interval prediction model of recent information of identical dimension for group-pile foundation settlement is established, By using this model, a more better precision will be got.With the listed above analysis the main characteristics of settlement behavior and the main factors of group-pile foundation displacement can be fully understood. Besides, the FEM and prediction method of gray theory can be discussed which may supply a in datum and technique for the design and construction of high-speed railway and references to the similarity. It is definite value in practice.