Numerical Simulation Based On Deformation Control Of The Retaining Structure In Deep Excavation Pit In Taifeng Lu Station, Nanjing Metro

Excavation engineering is a typical geological engineering problem, which is vulnerable to surrounding geological environmental conditions and has a high degree of sensitivity and complexity. Traditional analysis methods are difficult to accurately reflect the stress and deformation characteristics of a pit, therefore it can not meet the designing requirements. The finite element analysis, however, can simulate the deformation of the soil and internal forces of retaining structures during excavation. And the result is intuitive and reliable, which provide a reference for the subsequent designing and construction.By comparing the results between Hardening Soil (HS) Model and Mohr-Coulomb Model in PLAXIS program, the advantages of the HS model in deep excavation process simulation are analyzed. Take the deep foundation in Taifeng Lu Station, Nanjing Metro for example, this thesis applied a two-dimensional numerical simulation about the development of deformation in the internal support retaining structure as the excavation process proceeded. And the thesis analyzed the buried depth of retaining structure in order to study the ground-surface settlement, bottom uplift, displacement of the supporting structure and the impact on the surrounding environment during excavation.The main achievements are as follows:(1) Compare with the used constitutive model and determine the geotechnical constitutive models suitable for the numerical simulation of deep excavation process.(2) Analyze the parameters of HS model and determining related physical and mechanical parameters through experiments.(3) Take Taifeng Lu Station project, third line of Nanjing Metro for example, using hardening soil model of PLAXIS finite element program to simulate the whole process of deep excavation pit and applying the support. Analyze the size and deformation law of rock and soil as well as supporting structure in each condition. The results showed that:①Without support in the first step of the excavation, large deformation of supporting structures are observed;②It is the deformation value which is low at both ends and high at mid-point that represents on the envelope pile with support in each step during the excavation process. And the maximum displacement calculated is up to17.31mm;③The absolute value of the pile moment increases as the increment of the depth of the excavation, and the maximum value is1355kNm/m.④Compare the numerical simulation results with excavation site monitoring data, and analyze the reasonableness of the model, the parameter selection and the calculation method. Study the relationship between divert buried-depths of the supporting structure to the pit’s deformation. Finally, study the impact on the supporting structure of the diameter in the pit’s deformation.Through simulation analysis, if the axial force and stiffness of internal support and supporting piles, respectively, are constant, the buried depth of retaining piles recommended is22.2m.If the length and axial force of supporting piles and internal support are constant, the retaining pile diameter recommended is greater than0.8m.