Construction Optimization Of Super-shallow Buried Large-span Metro Station With Arch-cap Method In Upper Soft And Hard Stratum

A metro station section of Guiyang Metro is located in the city center.The area where the subway passes is narrow,the buildings on both sides are dense,the traffic volume and traffic volume are large,the pipelines are numerous,and the lines are complicated.According to the site survey data,the Quaternary artificial fill,red clay and underlying dolomite are covered in the site.The shallow depth of the station causes the station arch to be in soft soil.The blasting and excavation can easily cause the upper soft rock to deform or even collapse,thus affecting the overall stability of the station.Furthermore,above the station vault is the existing urban main road,the vehicle load may directly affect the station lining,which has a greater impact on the stability of the tunnel.Based on the urban rail transit project of Guiyang City,this paper takes a subway station as the research object,selects the “first arch cover method” to construct the subway station,and uses the indoor model test and numerical calculation to study the method.The applicability of the lower hard stratum is further optimized on the basis of the original construction method by analyzing the evolution process of the progressive failure of the surrounding rock,the force and deformation law of the arched arch,the stability of the side wall and the invert arch.Compare and analyze the original method and optimization method to ensure the feasibility of optimizing the method,and provide technical reference and scientific basis for its application in engineering.The main findings are as follows:(1)The “first arch cover method” has good applicability to large-span tunnels in upper soft and hard stratum.The upper arch cover can effectively ensure the stability of the arch and control the additional deformation of the construction.(2)Through the indoor model test,the progressive failure process of surrounding rock excavation without subway support is simulated.The test shows that the surrounding rock loosening starts from the arch and gradually develops to the vault.The subway station tunnel is the most risky during the tunnel demolition.The initial support is prone to damage and the tunnel is prone to collapse.Therefore,the timing of the appropriate arch cover is the key to ensuring the stability of the tunnel arch.(3)Through the indoor model test,the original construction method and the optimized construction method are used to excavate the construction process of the subway station tunnel,and the initial support deformation of the tunnel,the stress-strain of the mold arch and the road surface settlement law are obtained by two different construction methods.(4)Through the indoor model test,the tunnel loading damage after the completion of the construction is obtained,and the progressive failure law of the support is obtained.Due to the support of the arch cover,the bearing capacity of the arch is extremely high,and the side wall and the invert of the large arch are proposed.The strength determines the ultimate bearing capacity of the tunnel structure.(5)Through the three-dimensional numerical simulation,the progressive failure process and scope of the surrounding rock and the surrounding rock stress field,the bearingcharacteristics of the arched arch,the deformation characteristics of the initial support of the subway and the deformation characteristics of the side wall are carried out by the original method and the optimized method.Simulation and simulation,analysis and comparison of the advantages and disadvantages of the two methods,and compared with the indoor model test,to some extent verified the correctness of the indoor model test.