Research On Deformation Response Of Tunnel Surrounding Rock Based On Reserved Rock Pillar Construction Method

With the increasingly rapid urbanization process,rail transit plays an increasingly important role in urban transportation.In terms of saving travel costs and alleviating urban traffic pressure,the subway reflects its convenience and speed.The terrain conditions and construction environment of this article are relatively complex,which determines the difficulty of construction,poor construction conditions,and many engineering problems encountered are particularly complex.Due to the lack of research theories under similar conditions and the inability to fully adhere to engineering practice,based on the above research background,it is urgent to study the surface deformation,stability of the tunnel itself,and related control measures of shallow buried soft rock large cross-section subway stations.In order to solve the construction problem of subway stations under complex geological conditions with super large cross-section shallow burial and underground excavation,based on the actual engineering situation,combined with theoretical analysis and numerical simulation results analysis,compared with traditional subway station excavation methods,an innovative station engineering excavation plan combining initial support large arch cover and pre reserved rock column method is adopted to analyze the mechanical characteristics of each section during the excavation process and the impact of surrounding rock stability.The main research results are as follows:(1)By simulating and verifying the advanced deformation in the longitudinal section direction of the surrounding rock,which accounts for about 5% of the total deformation,it was found that the deformation of the surrounding rock mainly occurs within the range of 1D before and after the excavation face,and tends to stabilize after 4D.The control standards for deformation were determined according to the requirements of the specifications,and the deformation of the surrounding rock was controlled through the application of engineering measures.(2)Considering the actual situation of the project,a comparison was made between the construction schemes of the hole pile method,double side wall heading method,and reserved middle rock column method.Based on the ANSYS simulation results and engineering requirements,a construction method combining the initial support large arch cover and reserved middle rock column method was finally determined from the perspectives of stability,timeliness,economy,and durability.(3)The excavation simulation throughout the construction process was conducted.The settlement curve of the tunnel in terms of surface deformation,arch deformation,and peripheral convergence can be summarized into three stages: the initial slow change section,the middle rapid change section,and the final horizontal stable section.And as the excavation increases,the pressure on the arch,inverted arch,and side walls increases,indicating that the excavation and support of the upper steps have a significant impact on the longitudinal safety of the structure.The longitudinal force is obvious,and the longitudinal direction is the direction of tunnel excavation.The excavation and support of the upper steps is very unfavorable for the longitudinal safety of the initial support.The initial support pressure fluctuates greatly with the steps,and the arch waist pressure is the highest.Due to the superposition of tunnel excavation stress,the arch waist is compressed by the surrounding soil,resulting in the maximum stress after construction is completed.(4)Through simulation research on the excavation of reserved middle rock columns,using different widths of middle rock columns,removal lengths of middle rock columns,and burial depths as variables,the changes in surface,arch,side walls,middle rock columns,and stress were studied.When the width of middle rock columns is 0.3D and the removal length of middle rock columns is 8m,the ability to resist deformation is stronger.After the tunnel burial depth H=2D,the overall deformation trend tends to stabilize.(5)By calculating the settlement values of similar engineering projects and consulting the control standard values,considering the conditions of surface leveling and tunnel deformation,the maximum surface deformation of the tunnel on the surface and arch is 12.48 mm.After excavation of rock pillars,the Deformation monitoring value of the tunnel shows an increasing trend,the maximum deformation value appears at the vault,and the settlement value is 21.64 mm.