Study On Characteristic Of Initial Support Structure And Surrounding Rock Stability Of Shallow Underground Excavation Of City Subway Tunnel

With the expansion of city scale and the rapid development of economic construction in China,the problem of urbanization is becoming more and more serious,and rail transit plays an important role in solving the problem of urban traffic.In the underground tunnel construction of city,the traffic is dense,the population of people is large and the construction environment is complex and special.It is obvious that the deformation of tunnel surrounding rock is complex and changeable,and the support of surrounding rock is also complicated.For the shallow buried tunnel excavation,ground settlement,the displacement of surrounding rock,stress and internal force have great influence on the surrounding buildings.The deformation of tunnel surrounding rock is large,it is difficult to control it when it's beyond a certain warning value,the collapse and destruction of the tunnel are prone to occur,it's too serious to affect the construction safety of tunnel works.Therefore,the analysis method of finite element numerical simulation and field monitoring data can effectively control the deformation and failure of surrounding rock and supporting structure.The stability analysis of surrounding rock is the key to the safe operation and operation of urban shallow buried tunnel.This paper takes a section of Hefei Metro Line 2 as the research background,it adopts the method of tunnel theoretical calculation and analysis of finite element numerical simulation combined with monitoring data,research on supporting force characteristic,stability of the surrounding rock and other aspects of shallow buried tunnel structure,the main contents are as follows:(1)Deduce the formula of tunnel surrounding rock deformation and supporting structure according to the existing data at home and abroad,and determine the surrounding rock pressure of shallow buried tunnel,the size and characteristics of tunnel lining structure.(2)Deduce the calculation formula of supporting structure under the pressure of surrounding rock which is suitable for shallow buried tunnel through a large number of engineering examples and theoretical derivation.And check the theoretical formula with the application of HeFei metro project.(3)Compare and analyze the change of ground settlement,characteristics of internal force and displacement of support at initial stage with different constructionmethods of tunnel excavation through CRD method of establishing a two-dimensional numerical model and double side heading method construction.Calculate the results of tunnel model extraction the calculation,and axial force and bending moment,horizontal convergence displacement,vault settlement and displacement of tunnel bottom under the initial support of the deformed tunnel with different excavation methods.Analyze the change rule and draw a preliminary conclusion.(4)Obtain the results of displacement field,stress field and internal force of the initial support structure of CRD method with a two-dimensional numerical model and construction method of double side heading.Compare and analyze the two construction methods of CRD method and the method of double side found,it is found that the difference between these two methods is not very large.But in the surrounding rock stress field and internal forces of the supporting structure,the method of double side found is superior to CRD method.(5)Compare and analyze the monitoring data with data by establishing a three-dimensional numerical model for shallow tunnel construction,obtain the law of ground settlement and the change rule of the characteristics of the force,clearance convergence,vault settlement and ground settlement of initial support,it can guide the construction of similar tunnel engineering.(6)Conclude that the numerical simulation results are reasonable through comparison and analysis of actual monitoring data and numerical simulation results,and control excavation scale and excavation progress during excavation,and do the protection measures during excavation.The law of displacement and the maximum displacement value are basically consistent,which shows that the numerical simulation results are correct and reasonable.