Research On Deformation Characteristics Of Pile-anchor Composite Retaining Structure In Deep Foundation Pit Of Prefabricated Subway Station

In coastal cities such as Qingdao,deep foundation pit projects are often located in soil-rock combination stratigraphic structures.The construction is difficult,the engineering cost is high,and the depth of the pile into the rock is not enough,therefore,it is difficult to achieve the ideal support effect.In foundation pit engineering in a combination of soil and rock,a variety of support structures are often used to form composite supports to ensure the safety and stability of the foundation pit.At present,there is no current code to provide corresponding guidance for design and construction,so that more combined support is required.Refer to existing engineering experience.A large number of actual projects in Qingdao area show that the "pile-bracing-anchor" combined support system has better supporting effect in the soil-rock combination area and has significant economic benefits.However,in the foundation pit of the prefabricated subway station,due to the large construction load,the deformation control of the foundation pit is required to be higher.Therefore,it is of great significance to carry out the research on the deep foundation pit engineering of the prefabricated subway station under this support system.This paper uses the finite element program Midas GTS NX to combine on-site monitoring and numerical simulation based on actual engineering,Qingdao Rail Transit Line 6-Keluoshi Station.Through the simulation analysis,the overall 3D numerical model of the deep foundation pit of the station is established,and the deformation law of the layered excavation of the foundation pit is studied.The main research contents are as follows:(1)According to the actual project,formulate a foundation pit monitoring plan,conduct on-site monitoring,collect data on the deformation,the tension and surrounding surface settlement of the prefabricated subway station’s deep foundation pit enclosing structure,and conduct further detailed processing and analysis of the obtained data,and conduct an investigation and research on the prefabricated subway station.During the construction of the deep foundation pit of the station,the enclosing structure’s law of force and deformation,as well as the law of surface settlement surrounding the foundation pit,give data for the finite element numerical simulation that follows.(2)Perform a numerical simulation analysis of the construction process of "pilesupport-anchor" composite support foundation pit drilling using the finite element software Midas GTS NX to create a 3D model of foundation pit drilling in the actual soil layer.And calculate the model under various drilling conditions.It summarizes the stresses and deformations of the enclosure structure in the study,summarizes its rules,and compares them to actual monitoring data to ensure that the numerical model and parameter selection are sensible and reliable.(3)Based on the prefabricated structure of the subway station,a 160-ton gantry crane needs to be used to assemble the prefabricated components.In this paper,the bearing capacity of the foundation under the load of the gantry crane is checked to ensure the safety and stability of the foundation,The local three dimensional model after excavation was established,and the numerical simulation was carried out by using the gantry crane load,and compared with the field monitoring data.In addition,the influence analysis of gantry crane track beam foundation under different spans is also studied.