The Research And Application Of New Excavation Method For Large Section Subway Tunnel

With the rapid development of urban subway,China has built the largest subway network in the world,and has built a large number of large cross-section subway tunnels.At present,there are some limitations in the construction methods of large cross-section subway tunnels.The engineers constantly put forward new construction methods combined with specific circumstances to enrich the selection of construction plans.This paper takes Beijing subway as the background,according to the characteristics of large cross section of urban subway,through the research methods such as numerical simulation combined with field monitoring,and the Hole Guide method is analyzed and summarized.The paper will demonstrate the scheme and further optimize the design by the finite element analysis software Midas-GTS,and the paper will discuss the practical problems at the same time.The research results of this paper will be of great significance to the selection of the tunnel construction plan and the application of the Hole Guide method.The main research results of this paper are as follows:(1)First,the paper summarizes the limitations of traditional construction methods used in large section subway tunnels,and then put forward the Middle hole Guiding method for large section subway tunnel construction.The paper will establish the three-dimensional numerical model combined with the Beijing subway,and analysis the deformation law of surface,vault and hole convergence displacement,the stress characteristics of the initial support structure,and compared with the two side wall guide method and the CRD method the results show that the control of the Middle hole Guiding method is better than the other two methods during the construction process.(2)This paper will adjust the construction sequence of the heading holes in the Hole Guide method,the side heading will be excavated at the same time.Compared with the original method,it is found that the adjustment of the guide tunnel construction order reduces the bias stress in the construction process,improves the stress of the supporting structure,and has a positive effect on the stability of the structure and the control of the formation deformation.(3)Conclude the deformation law at the condition of different length of middle wall’s stratum and found that the deformation will decrease along the stratum length is shorter.But the removal distance is too short will lead to the increase of construction cost.When the 6m is removed,its deformation is not up to orange alert,so the demolition of 6m is the priority.(4)By comparing and analyzing the deformation law under different excavation footage,it is found that the lengthening of the excavation footage will lead to a large increase of the surface subsidence and the cross section deformation of the tunnel.It is easy to cause the related construction accidents.In the process of construction,it is necessary to strictly control the construction footage,and it is suitable for 0.5m.