Study On Mechanical Characteristics Of Prefabricated Subway Station Construction And Performance Of Anti-seepage Materials At Joints

Nowadays,China’s urban underground space has entered a period of rapid development.As an emerging technology,the assembly has been well applied in ground buildings,and its construction technology has been relatively perfect.However,the application of assembly technology in underground space is still in the exploratory stage,and most of them are tunnel lining prefabricated technology.The application of prefabricated subway stations is more limited.Compared with the cast-in-place station,the prefabricated station has the advantages of high production efficiency,fine components,rapid construction and less affected by the environment.At the same time,it also has many unfavorable factors restricting its development.For example,the prefabricated station is not a casting molding,but is formed by the assembly of prefabricated components,which also leads to the weakening of structural integrity and the frequent leakage of water at the joints.Therefore,based on the Jieda Road Station of Changchun Metro Line 2,this paper studies the mechanical mechanism,influencing factors of stability and anti-permeability materials at joints in the whole construction process of prefabricated subway stations.The main research includes:The three-dimensional numerical model of the station is established and calculated by FLAC3D numerical simulation software,and the mechanical characteristics of the fabricated station during construction are studied in depth;By changing the differences of key factors such as groundwater level and soil mechanical parameters,the sensitivity of these key factors to the stress-strain state characteristics of prefabricated station structure is studied;Dynamic Response of Prefabricated Station Structures under Seismic Loads;Based on the above research results,a cement-based composite waterproof grouting material mixed with polyethylene fiber and carbon fiber was developed by laboratory test analysis method to solve the leakage problem of joints between prefabricated components of prefabricated station.The mixed proportion of the new material with optimal performance was proposed,and its mechanical properties and impermeability were verified by test method to meet the engineering construction requirements.The main conclusions of this paper include:(1)During the excavation and construction of foundation pit of prefabricated subway station,affected by soil unloading and precipitation in foundation pit,the ground settlement outside the pit,the lateral displacement of diaphragm wall and the uplift of pit bottom will occur.At the same time,under the influence of diaphragm wall and its own gravity,the station structure will produce downward settlement and lateral displacement to the foundation pit.The assembly of the latter ring station will squeeze the diaphragm wall and cause the roof of the former ring station to produce small uplift,and this effect increases most significantly when the structure is assembled with the side wall.(2)During the assembly construction of prefabricated subway station,the maximum stress mostly occurs in the arch area of the station floor and the arch foot of the roof,and the maximum value increases with the increase of the number of assembly rings of the station.Therefore,it can be judged that this area is the most unfavorable and the first yielding failure position of the structure.(3)When the groundwater level decreases,the strain stress of foundation pit enclosure structure and station structure decreases significantly;The decrease of groundwater level has a great influence on the vertical displacement of adjacent stations,and the influence on the station roof is greater than that on the floor;The influence of lowering groundwater level on horizontal displacement of structures at different construction stages is roughly the same;After the groundwater level decreases,the Mises equivalent stress and the minimum principal stress have basically the same influence at different construction stages,while the maximum principal stress has different influence at different construction stages;After the groundwater level decreases,the pore water pressure at the joint of the station floor also decreases.The seepage velocity at the joint under different groundwater levels is k-2m>k-20m>k-30m.(4)When the elastic modulus,cohesion and internal friction angle of the soil increase,the mechanical characteristics of the station decrease to a certain extent.When the soil parameters change in a small range,the influence degree of soil parameters on the mechanical characteristics of the station from large to small is:elastic modulus>cohesion>internal friction angle;When the soil parameters change in a large range,the influence degree of soil parameters on the mechanical characteristics of the station from large to small is:elastic modulus>cohesion≈internal friction angle.(5)Most of the ground motion loads have horizontal disturbance effect on the assembled subway station structure,and the disturbance effect increases with the increase of seismic acceleration.The maximum Mises equivalent stress of the structure occurs inside the roof arch foot.(6)The compressive performance of the material with 0.4%carbon fiber was the most significant,while the polyethylene fiber had little effect on the compressive performance of the reinforced material;Adding polyethylene fiber can improve the toughness of the material.When the content of polyethylene fiber and carbon fiber is 2%and 0.6%respectively,the material has the best toughness and the ultimate strain is 2.25%;When the content of polyethylene fiber and carbon fiber is 2%and 0.4%,respectively,the impermeability of the material is the best,which is 43.08%higher than that of the material without fiber.