| With the advance of the modernization of the city,the development of the subway project has advanced by leaps and bounds.In the construction of subway station,the excavation of foundation pit and the initiation/reception of shield will have a certain impact on the surrounding environment of the station,the foundation pit envelope and the station structure.If the design parameters can not be determined reasonably,the overdesign or construction of the structure will be caused by light,and serious accidents will be caused by heavy.Only by clearly recognizing the subway construction effect under various design factors can we ensure the safety and economy of station design.Through the understanding of the current situation at home and abroad,it can be found that the existing research mainly focuses on the construction effect caused by the excavation of foundation pit and the section tunnel respectively,and there are few studies on the soil settlement,foundation pit deformation and the internal force of the ring frame beam and other important components caused by the double action of the foundation pit and shield tunneling construction of the station,and the related optimization design is even less.In this thesis,based on the Normal University Station of Xuzhou Metro Line 2Phase I project,taking the large mileage end well of the station as an example,Midas GTS NX finite element software is used to establish the formation structure model of end well,and the whole construction process of end well is simulated.The thesis adopts the research method of numerical simulation and comparative analysis.Firstly,it discusses the construction effect in the excavation and back construction stage of subway station under different design parameters.It concludes that:(1)in the excavation and back construction stage,the pile diameter of the enclosure pile has a great influence on the ground settlement and the internal force of the ring frame beam,but has a little influence on the pile side movement;Pile embedment depth has great influence on ground settlement,pile lateral movement and ring frame beam internal force.The influence of the pre-loading on the ground settlement and pile lateral displacement is small,but the influence on the internal force of the ring frame beam is great.(2)The surface settlement of the pit side,the lateral displacement of pile and the internal force of the ring frame beam are related to the symmetry of the foundation pit enclosure system and the size of the foundation pit span.Secondly,the thesis discusses the construction effect of the shield receiving stage,and concludes that the shield receiving will lead to the increase of the surface settlement value above the first built tunnel and the decrease of the surface settlement value at other locations.The receiving process of shield has a certain influence on the lateral movement of the retaining pile,and the influence on the internal force of the ring frame beam is large and complicated.Based on the above conclusions,the thesis also gives the reasonable parameters of the envelope pile and the pre-loading of the support.According to the stress characteristics of the ring frame beam in the construction stage,the thesis finds out the shortcomings of the traditional load-structure design method through comparative analysis,and puts forward the optimal design method of the ring frame beam,that is,reduce the bending moment of the end of the top frame beam of the load-structure model,and appropriately increase the bending moment and shear force of the local middle frame beam.Based on the optimization design of the ring frame beam of the project,the bending moment design value obtained is more safe and reasonable,and the reinforcement also saves the additional steel bar at the end of72 m diameter of 32 mm,and the optimization effect is better.The optimization design method of the ring frame beam has certain reference significance for other similar projects. |
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