Analysis On Influence And Construction Optimization Of Shield Tunnel Crossing Underneath Existing Bus Node Adjacently

Nowadays, the construction of Beijing subway is in full swing, and the subway traversing projects appear more frequently with the network density becoming higher and higher. When this kind of project is under construction, existing line is sensitive to excavation, following a disturbance. Especially when newly-built tunnel is adjacent to existing line, deformation of existing subway track and tunnel structure, crack and water penetration are easy to occur, these seriously impact the security of existing line operation, and it is risky. Maintaining safe use of existing subway is taken as a starting point and a ultimate goal, influences on existing bus node exerted by newly-built shield tunnel was studied and construction scheme was optimized. A guarantee of safe use of existing line and enriching this kind of project case to provide reference for similar projects are of great importance.This paper is based on the project of Beijing subway shield interval crossing existing transit node, testing and monitoring on-site and numerical simulation analysis are applied to the study. The main contents are as follows:(1) Before constructing, detection and assessment of existing bus node were performed, showing that it was in good condition. And during construction, existing bus node was monitored and toured, three aspects including deformation of monitoring points with driving distance, deformation of vertical section of bus node and deformation curve fitting were considered to analyze the deformation rule of tunnel structure existing bus node and track structure, influences on existing bus node caused by underpass construction. Brief analysis of deformation rule of track geometry and effects on a moving train imposed by underpass construction has also been made.(2) Based on actual project case, numerical simulation was performed, in the cases of pre-grouting and no grouting, deformation and stress of tunnel structure of existing bus node and track structure were compared and analyzed, the result showed that reinforcement by pre-grouting was of great importance. The actual measurement results was compared with the numerical calculation results, then the validity of numerical computing methods and rules was confirmed.(3) In the numerical simulation of existing bus node, different range of lateral grouting, various length of vertical grouting, diverse gabarit without grouting, different distance between centers of tracks of newly-built tunnels were optimized and analyzed, then changing laws of deformation and internal force were concluded, meanwhile optimized parameter was obtained to provide guidance for similar projects.