Analysis Of Influencing Factors Of A New Shield Tunnel Underpassing Existing Tunnel

With the continuous improvement of China’s urbanization process,the urban rail transit industry has developed vigorously,and the development and utilization of underground space has also ushered in the peak period of development.In the process of excavating new tunnels,various construction problems will appear,one of which is the problem of close construction of new tunnels.During the underpass construction of the new tunnel,it will inevitably cause secondary disturbances to the surrounding rock mass,which will change the original stress state of the existing tunnel structure,cause it to deform,and further induce cracks and water leakage in the lining structure.Such diseases will endanger the safety and stability of existing tunnels in severe cases.In order to ensure the normal use of existing tunnels as much as possible,it is very necessary to study the impact of new tunnel underpass construction on existing tunnels.Based on the construction of a newly built shield tunnel underneath an existing tunnel in a certain section of the Beijing Subway,this paper mainly does the following work:(1)Collect and sort out relevant documents about newly-built tunnels at home and abroad under-passing existing tunnels,and introduce the design overview and stratum properties of the project to provide a basis for the subsequent chapters of research.(2)Summarize the common diseases and their causes of existing tunnels caused by the underpass construction of new tunnels,and discuss their treatment measures against lining cracks,water leakage,and mud and mud on the track bed;Reinforcement measures both key parts of the tunnel construction through the new tunnel under the summary to ensure the security and stability of the existing tunnel structure wear under construction.(3)According to the types of tunnel under-passing construction problems and the division standard of the relative position relationship between the two tunnels,it is judged whether there are under-passing construction problems in the new and old tunnels.Collect and summarize the construction control standards of the new tunnel underpassing project,explore the safety judgment criteria for the tunnel underpass construction problem,and discuss the control standard for the tunnel underpass construction problem from the two aspects of the structural deformation and strength of the existing tunnel.(4)Using MIDAS / GTS created through a three-dimensional finite element model of construction under the new tunnel,and the influence of the underpass construction of the new shield tunnel at different intervals and angles at the intersection on the deformation law and force characteristics of the existing tunnel was studied.(5)Based on the comparative analysis of on-site measured data and numerical simulation results,the rationality of the reinforcement measures adopted in the underpass construction of the newly-built shield tunnel in the actual project is evaluated.