| With the development of rail transit network operation, lots of constructions traversing the existing rail transit within the rail traffic protected areas are inevitable. The complexity and risk of traversing construction is very high. And it has very strict control standards. If not handled properly will result in both the structure and track deformation overrun, or even seriously affect the normal operation of rail transit. If not handled properly will result in both the existing structure and track deformation overrun, or even seriously affect the normal operation of rail transit. Shield method has been widely used in rail transit construction, and it has obvious differences in the aspects of method, risk control between shield method and traditional construction method. Especially small stiffness of the whole structure made by prefabricated segment erection and the weak ability to resist deformation difference, put forward a huge challenge to traversing construction in ensuring the safe operation of rail traffic under the premise.Combining metro double-tube shield tunnel closely-underneath-crossing the existing metro shield tunnel section in Beijing for the first time, numerical simulation and classification of engineering monitoring were used to analyze the deformation law of strata and existing structure influenced by traversing construction. Finally, the measures of risk management are summarized in detail.(1) The related research achievements of the mechanism on ground surface deformation caused by shield tunneling are summarized and analyzed comprehensively:Based on the extensive collection of research achievements, the source of shield method has been traced, and mechanism and regularity of strata deformation due to shield is the research focus. Meanwhile summarized domestic urban rail transit operations management approach in terms of protected areas, laid the foundation for academic research.(2) Based on numerical simulation analysis, a large-scale finite element simulation model has been established:Paper systematically analyzed and demonstrated background and construction parameters through the project, then used Ansys finite element software establishing large-scale three-dimensional model of new line grouting reinforcement and strata pre-reinforcement. By processing the calculated data, the law of stratigraphic and structural deformation is comprehensive summaried. According to the analysis results of the program, its typical stages of data were compared and analyzed to choose the optimal construction plan.(3) Using the classification of risk monitoring technique with real-time acquisition of the data of structure deformation during traversing construction, then Data analysis result were compared and analyzed:according to the characteristics of traversing construction, the monitoring methods that mainly for automatic monitoring, minorly for artificial monitoring was presented, and then reasonable distribution programs and monitoring frequency is determined. Summary of double tunnel traversed successively and many disturbances, existing shield tunnel deformation law of evolution is changed from the "V" type to "W" type. The impact on the existing structure of shield tunneling generally begins from1.1to1.3times of the diameter of the tunnel. Compared with the numerical simulation data, small differences between the data mainly because construction is real-time adjusting construction parameters in the real environment.(4) Impact deformation analysis of existing structures and strata in different shield spacing, depth and soil pressure, grouting pressure, etc.:The deformation of existing structures and strata in different shield spacing, depth and soil pressure, grouting pressure is thorough analysised by numerical simulation method. Based on summarying the rules of stratigraphic and structural deformation, risk control measures for the traversing construction was presented. |
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