| Subway has many advantages,such as punctuality,safety,efficiency,comfort and so on.Therefore,more and more cities in our country have built a subway system,which has gradually become one of the important transportation modes for urban residents to travel.As the artery of urban public transportation,the primary concern of the subway is safety.The completion of the subway brings concentrated crowd flow,making the subway a gathering place for commercial activities.With the continuous expansion of urban scale,urbanization problems such as tight land use and large population density have emerged in many cities in China,which has led to the development of modern buildings(structures)toward a higher and more intensive trend,resulting in proximity to or directly above the subway Large,deeper and closer complex foundation pit projects frequently appear in the area.Therefore,how to carry out excavation construction in the subway protection red line area to ensure the safe operation of the subway has become an important scientific research issue.First of all,this paper relies on the excavation of a foundation pit directly above a subway line that has been operated in a city,and based on the project site data and construction data,a " foundation pit-tunnel" three-dimensional finite element numerical model is established.In order to monitor the influence of the excavation of the lateral foundation pit of the tunnel within the 50-meter protection red line of the subway,on-site layered settlement monitoring was carried out.At the same time,according to the actual construction progress of the lateral foundation pit excavation of the on-site tunnel,the finite element numerical simulation is simultaneously launched.Finally,the numerical simulation data was compared with the field layered settlement monitoring data to verify the accuracy of the model.Subsequently,on the basis of the "foundation pit-tunnel" three-dimensional finite element model,referring to the reinforcement control methods used in successful cases in similar projects at home and abroad,and combining the project’s own characteristics,the excavation area of the foundation pit directly above the subway tunnel simulations of different prevention and control methods were carried out,and the deformation characteristics and feasibility of the tunnel under each method were analyzed.Among them,the simulated prevention and control methods mainly include: front end then middle+unreinforced method,jump position pumping+basic floor back pressure method,front end after middle+floor back pressure method,sequential excavation+floor back pressure method and more strict prevention and control methods: pumping strip+bottom plate back pressure+single row pile method,pumping strip+bottom plate back pressure+multi-row pile method.The results show that the different prevention and control methods have the following rules: row pile method>extracted strip excavation+floor back pressure method>unreinforced method;At the same time,among the prevention and control methods,the warning value of subway protection(10 mm)is not exceeded: pumping bar+bottom plate back pressure+multi-row pile method,pumping bar+bottom plate back pressure+single row pile method,tip end and middle part+backplate back pressure method,jump bar drawing+base backplate back pressure method.Finally,the prevention and control method of driving piles with ideal prevention and control effect is selected,and the parameters of single-row piles and multi-row piles are analyzed to explore the reinforcement characteristics and mechanism of driving piles under different parameters.Among them,the deformation characteristics of the tunnel and the value of the floating amount of the tunnel are mainly aimed at the parameters such as pile length,pile diameter,pile spacing,floor thickness,stacking,net spacing of the pile,and lateral building structure load.At the same time,it is hoped that through the research of this project,it will help to provide a basis for analogy reference for similar projects in the future. |
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