| Ningbo is located in the southeast coastal area of China,which is a typical soft soil area with high water content,high void ratio,high rheology and obvious regional characteristics.In the process of rail transit engineering construction in Ningbo soft soil area,studying the deformation characteristics of deep foundation pits under the effect of time and space has always been the focus and difficulty.Taking the deep foundation pit of Xingzhuang Road Station of Ningbo Rail Transit Line 5 phase I project as the engineering background,this paper analyzes the monitoring results on the spot,simulates the excavation process by using the finite element analysis software,and analyzes the influencing factors of the deep foundation pit deformation.The main research contents and results are as follows:(1)From the four aspects of deep foundation pit field monitoring,space-time effect,finite element analysis and deformation influencing factors,the deformation law and influencing factors(survey,design and construction)of main structure and surrounding environment of deep foundation pit of rail transit in soft soil area are analyzed theoretically.(2)The monitoring data collected from Xingzhuang Road station are sorted out,focusing on the analysis of deep horizontal displacement,surface subsidence,supporting axial force,underground water level outside the pit and wall top displacement.The results show that the different monitoring items of the foundation pit show that the deformation gradually increases with the progress of the excavation conditions,and the deformation near the standard section is significantly greater than that near the end well,and the deformation of the long side is significantly greater than that of the short side and the middle of the long side.The deformation is the largest,showing obvious space-time effects.(3)The three-dimensional model of deep foundation pit is established by using finite element analysis software to simulate the excavation process,analyze the simulation results of deep horizontal displacement and surface subsidence under different working conditions and different positions,and analyze the rationality of the model by comparing with the field measurement results,so as to lay the foundation for the analysis of influencing factors.(4)By means of finite element analysis,the influence factors of soil parameters and design in investigation factors,diaphragm wall thickness in construction factors,prestress of steel support,support erection time and ground overload are analyzed by controlling single variable method.The sensitivity analysis is carried out on the deformation of deep foundation pit caused by the change of soil parameters,so as to identify the relevant factors affecting the deformation,and to optimize and summarize the technical points of the design and construction of deep foundation pit of rail transit considering the space-time effect.The results show that the change of compression modulus and internal friction angle of different soil layers have a greater impact on the deformation,while the change of cohesion has a smaller impact on the overall deformation.Controlling the continuous increase of the thickness of the diaphragm wall,applying the prestress of steel support and adding it in time,reducing the exposure time of the foundation pit without support,strictly prohibiting over excavation and strictly controlling the surrounding external load,so as to limit the deformation of the foundation pit to the greatest extent. |
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