| The urban rail transit of Ningbo city has been constructing in a rapid speed since2008. Due to the behavior of soft soil in Ningbo area, there exists a latent danger of instability in the deep excavation engineering which can affect the safe use of adjacent buildings. Although, full attention has been paid by design, construction and management department to this problem, systematical study on the design technique, calculation technique, and deformation law of foundation pit is lacked in Ningbo area and the theory study lags far behind the practice. Therefore, the deformation behavior of deep excavations in rail transit project of Ningbo are investigated based on a series of data analysis by using probability and mathematical statistics, finite element method, and back-analysis mehtod in this paper. The main content of this paper includes:(1) A database which includes details data of deep excavations in Ningbo (13cases), Shanghai (49cases) and Hangzhou (28cases) is developed, and the behavior of deformation of the deep excavations in three areas are also compared. On the bases of measured data, the range and mean value of the maximum lateral displacement of bracing of foundation pit are proposed. The influence of such factors as thickness of soft soil above wall toe, embedded depth ration of wall, system stiffness, factor of safety against basal heave, ratio between the sectional area of piles and the excavation area, and location of first level strut are discussed on the stability of deep foundation pit. Furthermore, the range and mean value of the maximum ground settlement are also proposed and the surface settlement patterns, settlement envelope equation as well as surface subsidence prediction formula are developed, then the effect factors on the ground settlement are studied, in addition, the range and law of bottom heave, vertical displacement of top of wall and piles, and the change rule of strut axial forces are analyzed. Finally, the similarities and difference of deformation behavior in three areas are compared. The results of this paper can give a reference on design, construction and management.(2) Lateral displacement of wall, vertical and lateral displacement of wall crown, settlement of ground, settlement of pipelines, settlement of column, settlement og bridge, change of water level, change rule of strut axial forces are analyzed by taking deep excavation of Yinghua park station for instance. Then, the general law of deep excavation in Ningbo urban rail transit project is verified. On this basis, the similarities and differences between design deformation and measure deformation and the factors influencing the displacement on design deformation behavior are discussed. The results can present technical supporting for the optimal design of deep excavation in Ningbo area. (3) A systematical study on behavior of deformation of deep excavation in Yinghua park station, Ningbo rail trantsit project, is carried out by using3-D finite difference method. Horizontal displacement of wall, settlement of surrounding ground, horizontal displacement of ground, displacement of deep ground, base heave, lateral earth pressure of wall, vertical pressure of base, change rule of strut axial forces and vertical pressure of wall are analyzed. Furthermore, influence of thickness of diaphragm wall, style of foundation reinforcement, design parameter soil test and supporting style on the deformation are discussed and optimal design advices are presented.(4) Taking Yinghua park station for instance, back-analysis of displacement is executed on the coefficient of lateral resistance of ground, i.e.,’m’, which is an important parameter in design of foundation pit. The influence of the parameter ’m’ on deformation of design is discussed. Then, the back-analysis is carried out on the parameter ’m’ for different layers of soil in different excavation depth based on measured data, and the deformation is predicted at the same time. Finally, the recommended values of ’m’ for different layers of soil are presented. |
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