Theory And Application Of Prefabricated Open-cut Metro Station Structure

Since the rapid development of urban rail transit in China in 2000,it has maintained a high-speed growth trend.All cities are facing tremendous pressure in terms of construction period,environmental impact,labor shortage,project quality,etc.The traditional open-cut metro station structure is generally constructed by cast-in-place construction technology,which has many construction links,slow construction speed,serious construction dust and noise pollution,a large number of on-site workers and high labor intensity,difficult project quality control,frequent leakage,and it is greatly affected by the climate conditions.Prefabricated building structure has significant advantages of high efficiency,high quality,green and environmental protection,and is widely used in the field of aboveground construction,especially in developed countries such as Europe,America and Japan,while the application of underground structure is mainly concentrated in shield tunnel engineering.In order to solve the problem of winter construction in the former Soviet Union,the prefabricated technology was studied and applied in the open-cut metro station and shield-driven tunnel structure engineering.Due to the limitations of early technology,the large-scale metro station mostly adopts the prefabricated rectangular frame structure with relatively complex system,and the joints are mainly connected by cast-in-place concrete,so the prefabrication advantage is not obvious.The prefabricated station of Changchun Metro Line 2 is a two-story single arch long-span structure with open excavation.The mortise-tenon joint connection between prefabricated components without wet operation of cast-in-place concrete is adopted for the first time,which belongs to the fully prefabrication mode.Compared with the aboveground structure,shield tunnel or foreign prefabricated structure with cast-in-place joint,this prefabricated metro structure has great differences in the use of environmental characteristics,stress characteristics,waterproof requirements,construction technology and other aspects.Therefore,the previous main technical experience cannot be applied,this new prefabricated technology needs different solutions and methods,and through systematic in-depth research to establish a new technical system.This paper focuses on the research and solution of the scientific and technical problems supporting the practical application of the prefabricated technology of metro station.Through theoretical analysis,indoor test research and in-situ test and verification,it focuses on key technologies of prefabricated underground structure,covering the bearing capacity of the joints of the prefabricated structure components,the static and dynamic mechanical behavior of the prefabricated structure system,the mechanical characteristics of the lightweight structure components,and joint waterproof technology.The above research has formed all-round theoretical and practical results from the whole mechanical behavior(static and dynamic)to the local mechanical characteristics(joints and components)of the prefabricated station structure.The main academic achievements and the contribution are as follows:1.A new type of "grouted mortise-tenon joint" is proposed and developed.A series of 1:1 prototype joint mechanical properties tests are carried out for different joint types,different grouting materials,different grouting ranges,different axial forces and bending moment combinations.Based on the analysis of the deformation characteristics of the joint,the stress-strain laws of the concrete structure and the reinforcement,combined with the finite element analysis and theoretical research,the principle of the bending resistance,the bending and shear bearing characteristics and the mechanical constitutive relationship of the joint are deeply explored.The failure mode,the multi-stage bearing characteristics and the "variable stiffness" characteristics of the joint are revealed,the joint stiffness calculation formula,bearing capacity calculation method and joint structure design standard are put forward,and the mechanical theory of grouted mortise-tenon joint is preliminarily formed,which strongly supports the establishment of prefabricated structure system and lays a solid foundation for the research and application of prefabricated technology in metro station.2.The mechanical behavior of prefabricated station structure system under static and dynamic action is studied.The numerical models of two-dimensional,threedimensional,multi-construction stage,multi-use stage,multi-load condition and multi-structural parameters are established.The internal force,deformation and development process of the prefabricated structure system are analyzed in detail.The comparison with the cast-in-place concrete continuous structure of the same shape is carried out.The static and dynamic mechanical behavior of prefabricated structure,the influence law of joint stiffness,different auxiliary support measures,fertilizer tank and cover soil backfill on the mechanical behavior of the structure are mastered.This paper also reveals the characteristics of amplitude modulation and protection of the prefabricated structure joints to the structural system bending moment,and demonstrates that the prefabricated structure has better ground following characteristics and superior overall seismic performance than the cast-in-place structure under the seismic action.Through the in-situ test of several completed stations,the theoretical analysis results and the safety and reliability of structural design are verified.3.A new type of "closed cavity thin-walled component" is proposed and developed.In view of the characteristics of large volume and difficult lifting and assembling of large-scale underground structure components,the lightweight prefabricated components with closed cavity are formed by using the lightweight core mold of bubble concrete as the filling material,which realizes the lightweight of large-scale prefabricated underground structure components.At the same time,the mechanical behavior of the closed cavity thin-walled components is studied deeply,the unique shear lag effect and shear stress distribution law of the normal section are revealed,the reasonable cavity ratio index of the closed cavity thin-walled components and the reasonable structural design parameters of the key parts such as flange plate,rib plate,diaphragm,end plate and chamfer are put forward,which lays the theoretical and practical foundation for the future application.4.A complete structural waterproofing system of prefabricated metro station is established,and the joint waterproofing technology of prefabricated structural joint is mainly studied.The method with multiple waterproofing defence lines of “two cushions,one grout,one caulking” is put forward,that is,two hydro-expansive rubber sealing cushions + grout with modified epoxy + one caulking.Through the test,the waterproof performance of single and double rubber sealing cushions and the waterproof strengthening effect of composite expansion rubber sealing cushions are revealed.The test shows that the waterproof performance of single rubber sealing cushions can withstand water pressure up to 1.0 MPa under the most unfavorable conditions of joint width of 10 mm and cushion dislocation of 5 mm.From the actual use of the station at present,when the station structure is not provided with an external waterproof layer,there is no leakage of water in the structure,which achieves the expected good effect.The main research results of this paper are of great significance in both theory and practical application.The research results effectively support the successful implementation of the first prefabricated station in China.At present,five prefabricated stations of Changchun Metro have been put into use,and it will be popularized and applied in more than 10 stations in the next round of urban rail transit construction in Changchun City and other cities in China.At the same time,the research results also lay a theoretical and practical foundation for the further development of large-scale underground structure prefabricated technology.