Mechanics Effect Analysis On Shield Tunneling In Close Proximity By In-situ Monitoring And Numerical Simulation

With the rapid development of rail transportation in major cities, undergroundspace is developed and utilized. The shield tunnel method is used widely with itsadvantages of high degree of automation, high speed of construction, weather—proofcharacter and less impact on the ground buildings and traffic. However, in the centralarea of the city, influenced by the surrounding environment, geological conditions andthe existing pipeline, sometimes the distance between the two tunnels is designedshortly. A large number of the tunnels are built which are close to the constructedtunnel. The accident of pipeline deformation or cracking occurs frequently. So it isvery important to analyze the interaction of shield tunnels construction in closeproximity and effective measures must be taken to minimize for protecting existingtunnel. This problem is attracting more and more scholars.Setting the project of Beijing subway line10as an example, the changingregularities of the constructed tunnel segment stresses are analyzed. The maincontents are as follows: the segment monitoring data was summarized; lasted curvesof the segment secondary stresses were given by analysis of the measured data.Numerical simulation method was used to get the impact of the constructed tunnelstresses, vault settlement and tunnel convergence by establishing three-dimensionalmodel. The changing regularities of the constructed tunnel stresses and surfacesettlement are researched. In this paper, the main conclusions are as follows:1) By analyzing the monitoring data, the conclusions are obtained as: thecircumferential secondary stressesθand the longitudinal secondary stresseszwerecarried out in the constructed tunnel on the close proximity tunnel construction. Thesesecondary stress experienced five stages, including small transformation, dramatictransformation, mutation stage, the steady transformation and stabilization stage. Thecircumferential secondary stressesθand the longitudinal secondary stresseszwillbe pressure or tensile. The magnitudes of the circumferential secondary stresses willbe greater than those of the longitudinal secondary stresses.2) With the numerical simulation of the actual conditions and different spacing,the conclusions are obtained as: when the distance between two tunnels is decreasing,the constructed tunnel stresses will gradually increase, and the magnitudes of the secondary stresses will increase obviously. The maximum surface settlement willmove to the midpoint of the two tunnels, and it will become bigger and bigger and getsteady when it ’s away from the section. Tunnel internal forces, surface subsidence,dome subsidence and lateral convergence have shown a significant way. When theheading face did ’t reach the section, numerical values is stable. When the headingface is reaching the section, the values have an obvious mutation. After passing thesection, the values are going to stabilize.3) By comparing the experimental results with simulation results, it will be foundthat the changing regularities of the advanced tunnel segment stresses are basicallysame. When the distance between the shield driving face to the measured sectionbecomes from negative100meter to100meter, the magnitude of the secondarystresses will change obviously. When the shield driving face passes through100meter,the magnitudes of the secondary stresses will be basically unchanged. The resultsshow that it’s feasible and of great application value to monitor the additional stressby adhering strain gauge to the surface of the constructed tunnel.