Study On The Permissible Value And Technique For Deformation Controlling Of Underground Construction Crossing Existing Metro Line

As the urban rail transit networks of China are built at a large scale, crossing project between different lines becomes inevitably. These crossing projects are directly related to the operation safety, construction safety of under construction project, constructing period and cost of the metro lines, and cast new challenge on the construction and development of metro. Although there have been some successful cases of new-built metro lines crossing existing metro lines encountered during the metro construction in Beijing, Shanghai and other cities abroad, integrated technical system has not been formed, and sophisticated deformation controlling standard has not been achieved, furthermore, the price of existing crossing measurements are worthy of studying.Based on the summarization of former engineering experience and achievement, in combination of classical crossing case, International Airport Line of Beijing Urban Rail Transit under (upward) crossing the behind-station turn back line of existing metro line, urban rail 13th, this dissertation systemically studies the problem of underground projects crossing existing metro line, and attained the following results.(1) Domestic and abroad classical cases of underground projects crossing existing metro lines are analyzed, and the classification and characteristics of these projects are studied.(2) The related factors influencing the deformation of existing metro lines in crossing engineering are analyzed, based on which the characterization value of deformation controlling code are proposed.(3) Deformation controlling code of existing lines, including tunnel structure deformation controlling and track structure deformation controlling standard are put forward. The establishment of track structure deformation controlling standard should follow the principle of being beneficial to maintenance. The confirmation of tunnel structure deformation controlling standard is mainly involved with two factors, the present bearing capacity of existing structure and the impact of construction on existing line. In regard of confirmation of these two factors, complete computing and analysis are prerequisite, and the smaller one can be taken as the tunnel structure deformation controlling standard. And also the tunnel deformation controlling standard must give way to the track structure deformation controlling requirement. To be beneficial to implementation and control, using of controlling standard should follow the principle of considering different areas, classes and stages.(4) Synchronous lift-up technique is a kind of active controlling measure, and it is effective of making lift-up plan that following the principle of considering different areas, stages, groups and classes. The core of lift-up controlling is improving the occasion, which means dynamic adjusting the collocation and distribution of jack according to the deformation situation of existing lines. Taking guardrail, combining monitoring and line adjustment methods, are lash-up method of making sure the safety of existing line operation.(5) In order to ensure construction and operation safety, automatic and artificial monitoring should be taken in crossing projects. It is important to establish the information feed-back system. Monitoring data indicates that the deformation process is floating-subsidence-tending to stabilization-stabilization. The accumulative total deformation of tunnel structure and track structure is within 13.5mm, which indicates that lift-up controlling technique can control deformation effectively.