Study On Expanding Scheme Of Large-section Existing Tunnel

Large-section existing tunnel expanding is a tunnel construction method developed in recent years to solve the problems such as aging of existing tunnel structure,durability failure and insufficient traffic capacity.It is different from the ordinary one-time-shaping tunnel excavation in section,span and excavating process,and its stress redistribution and structural stress are more complicated.In this paper,the methods of literature investigation,numerical calculation,theoretical analysis and field monitoring are used to study the expanding scheme of existing tunnel with large section,which can provide reference for the design and construction of similar existing tunnel expanding projects with large section.The main research work and conclusions are as follows:(1)Investigate the domestic and foreign cases of existing tunnel expanding with large-section and the research status of tunnel-expanding methods,survey the theoretical and experimental research by domestic and foreign scholars on existing tunnel expanding with large-section,and put forward the problems existing in the current research at home and abroad.(2)Based on the project profile and engineering roadblock of the project-based,this paper analyzes the factors affecting the stability of surrounding rock and the basic tunnelexpanding methods,puts forward a variety of feasible construction schemes,and discusses different expanding schemes.(3)The three-dimensional finite element model was established by using MIDAS GTS NX software,and the calculation under different expanding schemes was carried out.The characteristics of vault settlement,surrounding rock stress,plastic zone distribution and support stress under different tunnel-expanding schemes were selected for construction mechanics analysis.(4)Based on the Analytic Hierarchy Process,the importance coefficient of each index is set according to the construction conditions and difficulties of the project-based and the AHP calculation results are obtained.Ultimately,the "one-side first left-side then top-side" scheme is determined as recommended scheme.(5)By monitoring and measuring the project-based,the characteristics of surrounding rock pressure,arch internal force and top settlement in the test section during the tunnel expanding process are analyzed,and the variation of surrounding rock deformation and support stress under the recommended expanding scheme are obtained,and the application effect of the recommended expanding scheme is evaluated.In addition,the monitoring data of top settlement are compared with the numerical simulation results above,which verifies the rationality and effectiveness of the numerical model parameters and modeling method above.