Research On The Theory And Application Of The New Column-arch Method For The Construction Of Shallow Buried And Large-section Subway Station

Urban rail transit has rapidly developed in large and medium-sized cities worldwide as it can solve problems such as ground traffic congestion,land scarcity,and air pollution that cities face during development.Subway stations,as a critical and difficult part of urban rail transit projects,are often located in the city center with extremely complex surrounding environments.Therefore,the selection of construction methods is particularly important.Different regions often choose appropriate subway station construction methods based on their geological conditions and surrounding environment,or improve existing methods based on the characteristics of the project,gradually leading to the emergence of many new construction methods for subway stations.This article relies on the Beijing Road Station project of Guiyang Metro Line 3,and uses theoretical analysis,numerical simulation,comparative analysis of construction methods,and optimization design to study the proposed new construction method of the hidden excavation large-span subway station using a column-arch method.The main work and research results are as follows:(1)The calculation theory of surrounding rock pressure in each stage of subway station construction with new column arch method is studied.Considering the excavation of rock mass,the construction process of subway station with new column arch method is divided into three stages : the excavation stage of lower pilot tunnel,the excavation stage of upper pilot tunnel and the excavation stage of residual rock mass.Based on the applicability of various surrounding rock pressure calculation theories,suggestions for the calculation theory of surrounding rock pressure applicable to each construction stage are proposed.(2)According to the actual working conditions,FLAC3 D finite difference software is used to simulate and analyze the construction of subway station with new column arch method.It is found that the surrounding rock is mainly subjected to compressive stress during the construction process,which changes with the transformation of construction process,mainly distributed in the arch waist of guide hole,temporary support and side wall corner of station.Before the construction of beam and column,the primary support and temporary support are the main stress structure,and after the construction of beam and column,the steel pipe column is the main stress structure.The stress surge occurs in the steel pipe column after the temporary support is removed;the surface settlement basically conforms to the law of Peck settlement trough,and No.3 and No.4 pilot tunnels have the greatest influence on it.The vault settlement of No.3 and No.4 pilot tunnel and station vault is larger,and the convergence value of arch waist of No.1 and No.2 pilot tunnel is the largest.The excavation of pilot tunnel and removal of temporary support are the construction processes with rapid change of vault settlement.(3)By comparing and analyzing the new column arch method,the Centre drift method and the PBA method,the advantages and disadvantages of the new column arch method compared with the other two methods are explored.It is found that the new column arch method is the most superior to the arch waist settlement control in terms of stratum deformation.The control of surface settlement and vault settlement is basically the same as that of the PBA method,which is better than that of the Centre drift method,but the new column arch method will have a sharp increase in deformation during the construction process.In terms of stress change,the stress of each position of the new column arch method is larger than that of the other two methods,but it is still within the safe range.In terms of construction organization characteristics and benefits,the new column arch method is theoretically superior to the other two methods in terms of construction period,construction safety,construction quality,economic indicators and construction difficulty,but lacks practical engineering application experience.(4)Based on the construction characteristics of the new column arch method,the construction optimization scheme is proposed and compared with the original scheme.It is found that the optimization scheme can effectively avoid the stress surge of the steel pipe column and ensure the safety of the steel pipe column during the construction process.The control of stratum deformation is better than the original scheme,which solves the problem of excessive deformation rate caused by the removal of temporary support,and improves the difficulty of vibration,roof punching and compactness control of vault lining in practical engineering.Finally,the new column arch method optimization scheme was successfully applied to practical engineering.(5)Based on the actual engineering application of the new column-arch method,it is shown that the new column-arch method successfully utilizes the concept of stepby-step construction with small pilot tunnels to complete the construction of the central vertical force system when the excavation section area is small.Under the support of the central vertical force system,the rock mass on both sides is excavated to complete the construction of the station’s top support structure,which can reduce the amount of temporary support and greatly save construction costs.Meanwhile,the use of this construction method controls the construction deformation and support stress within the prescribed range,ensuring construction safety,and can accelerate the subsequent construction speed,thereby shortening the construction period.