| In order to solve the problems of long construction period,low efficiency,construction pollution,labor supply and demand in the construction of urban rail transit,Shenzhen has taken the lead in demonstrating,responding to national policies,and exploring and practicing the construction mode of prefabricated underground stations.Shenzhen,as the leading and demonstration city of new building industrialization represented by prefabricated buildings,has gradually formed a unique prefabricated building Shenzhen model through policy guidance,market operation and industry self-discipline.The prefabricated subway station construction technology was first used in the fourth phase of the Shenzhen Metro Line.This article introduces the overall design scheme of the prefabricated subway station under the internal support system,and analyzes the stress and deformation of the main structure and enclosure structure of the prefabricated station.In order to further promote the construction technology of the prefabricated station and achieve standardization,modularization,and scale of the construction of the prefabricated station,Provide theoretical guidance.The research content and achievements of the thesis are as follows:(1)The overall design scheme of the prefabricated station under the internal support system in Shenzhen is summarized.The structural section form of the station is based on the structural optimization design of Changchun Yuanjiadian Station,the first fully prefabricated underground station in China.The outer lining is a single-arch large-span prefabricated station composed of four prefabricated components;The circumferential joint of the station adopts grouted mortise joint,and the longitudinal connection adopts the longitudinal connection steel bar,which is tensioned and locked ring by ring;In order to reduce the weight of a single prefabricated component and facilitate transportation and assembly,the prefabricated component is designed in a lightweight way,that is,the closed cavity thin-walled component is used;The design of the ring frame beam at the entrance and exit breaks the traditional idea of building first and then opening the hole.The prefabricated rectangular ring frame is adopted,and the mortise and tenon connecting with other components are reserved during the design;The beam and column system of the station middle plate is composed of prefabricated middle plate,prefabricated middle longitudinal beam,prefabricated middle column and cup foundation;The station waterproofing system consists of structural concrete self-waterproofing,joint waterproofing,interface waterproofing of cast-in-place and prefabricated sections,and leakage water treatment.(2)Combined with the engineering geological conditions of the station and the construction process of the prefabricated station,the ground structure model is established by using ABAQUS finite element analysis software.The deformation law of the foundation pit,the change law of the axial force of the support and the stress characteristics of the inverted continuous support during the construction of the prefabricated station are emphatically analyzed.Firstly,the deformation of the foundation pit of the prefabricated station is analyzed,which is mainly divided into the excavation stage and the station assembly stage.The total deformation of the diaphragm wall is 10.31 mm,and the diaphragm wall accounts for a large proportion in the excavation stage,accounting for 88.6% of the total deformation.The deformation trend of the foundation pit during the excavation process is consistent with that of the cast-in-place station;In the process of support switching and structural assembly,the deformation of diaphragm wall accounts for 11.4% of the total deformation,with a variation range of 0.05～0.99 mm.The magnitude and range of deformation are quite different from those of cast-in-place stations;Secondly,the process and stress characteristics of support removal and replacement are analyzed.Support removal and replacement are important construction steps in the construction of prefabricated stations.The temporary axial force of the middle plate near the support removal ring is large,accounting for 80% of the axial force of the whole support replacement.Therefore,the number of 1 ring of continuous support close to the support replacement can be appropriately increased when arranging the continuous support,and the number of 1 ring of continuous support far away from the support replacement can be reduced;Finally,the results of numerical calculation and field monitoring are compared,and the change laws of the two are basically consistent,which verifies the effectiveness of numerical analysis.(3)Using ABAQUS finite element analysis software,a load-structure model is established to analyze the mechanical characteristics of a single arch and large span prefabricated station under short-term and long-term operating conditions.The effects and laws of different lateral pressure coefficients,different formation bed coefficients,different soil layers,and different overburden thicknesses on the deformation and stress of the underground station structure under two operating conditions are explored,providing theoretical basis and structural design guidance for the adaptability of the prefabricated station structure to the stratum.The results show that the lateral pressure coefficient has a significant impact on the mechanical properties of the station structure when the formation bed coefficient remains unchanged.When the lateral pressure coefficient increases from 0.35 to 0.75,the axial force in the roof span increases by6.99% under recent operating conditions,and the axial force increases,constraining the structural deformation;When the lateral pressure coefficient of the formation is constant,the larger the subgrade coefficient,the harder the formation,and the increased axial force on the structure,which restricts the deformation of the structure,making the structure more stable;When the structure above the middle plate of a prefabricated station is located in the hardest fully weathered biotite granite layer in the analysis,the bending moment of the roof is reduced by 386 k N·m compared to the plain fill layer in recent working conditions,indicating that the better the stratum conditions,the safer the structure;The greater the thickness of the covering soil,the greater the internal force at the arch crown span and arch foot.The thickness of the covering soil at the station has a significant impact on the internal force of the structure. |
