Study On Calculation Theory And Field Test Of Integral Pile-Raft Structure In Beijing-Shanghai High-Speed Railway

The high-speed railway integral pile-raft structure applied in deep Quaternary foundation with medium compressibility can effectively control the total settlement and differential settlement of the subgrade as a simple structure which is easy to construct with good technical and economic indices. In light of little research on design and calculation theory of this structure, aimed at the subgrade load characteristics and the structure characteristics, analysis of such issues as the design and calculation theory, structure-soil interaction and the dynamic response under the moving train load is of practical significance.The two-dimensional equivalent frame method applied for design and calculation of high-speed railway integral pile-raft structure is proposed in the background of Beijing-Shanghai high-speed railway on basis of a fully investigation of the application of such structure at home and abroad and a deep comparative analysis of the subgrade load characteristics and settlement control standards of the high-speed railway engineering different from those of the building engineering. The pile-soil interaction and raft-soil interaction are discussed and influence analysis of important parameters of the structure is done with the method which simulates the pile-soil interaction with node springs and raft-soil interaction with linear springs.By comparing the two-dimensional and three-dimensional methods, it is found that the three-dimensional frame method can comprehensively reflect the space distribution of internal forces in the structure, but the calculation is more complicated while the two-dimensional equivalent frame method is simple and the calculation results are safer which is verified to be rational and feasible. The settlement of the structure is calculated using a variety of methods introduced in correlative codes or standards based on the specific subsoil characteristics and structural characteristics in Suzhou station of Beijing-Shanghai high-speed railway and accordingly the settlement calculation method is proposed that suits for high-speed railway integral pile-raft structure.Secondly, the three-dimensional dynamic simulation of the structure is carried out, using the one-way loading mode of the train load, which explores the dynamic response and the relationship between dynamic response and the train speed as well as the embankment height. Calculation results show that the maximum longitudinal and vertical dynamic stresses of the raft, the maximum vertical dynamic stress of the pipe piles and the maximum vertical stress on top of the embankment decrease as the speed increases whereas the maximum transverse dynamic stress of the raft increases and then decreases with the speed increase. The accelerations of different parts of the structure increase with the increased speed. The maximum vertical dynamic stresses of the raft and pipe piles decrease as the embankment height increases.Finally, it indicates that the actual stresses and deformation characteristics of the structure are consistent with theoretical calculations based on the field test of integral pile-raft structure which verifies the theoretical method is of feasibility. The settlement of the structure can meet the settlement assessment guide according to the settlement assessment which show the pile-raft structure can effectively control the settlement after construction.