Risk Assessment And Stability Analysis Of Shield Tunneling Through High Pressure Natural Gas Pipeline

With the rapid development of rail transit construction and the increasing traffic pressure,urban rail transit has gradually become a mainstream travel mode for people.The shield method is widely used in subway tunneling projects because of its convenience,low ground disturbance and high degree of automation.While urban rail transit is being built,the ensuing safety hazards cannot be ignored.In the shield tunneling project studied in this paper,the shield tunneling makes the natural gas pipeline a great safety hazard in the close under-passing of high pressure natural gas pipeline.Therefore,this paper combines the risk evaluation method and numerical simulation analysis to study the overall stability of the shield tunnel close under-passing high-pressure natural gas pipeline project,propose suitable reinforcement measures and optimize the reinforcement scope.The main contents and results are as follows:(1)Based on the high risk factors existing in the close under-passing of high-pressure natural gas pipeline by the shield structure of the subway,the possible risks during the construction process are evaluated,and the natural gas pipeline risk is identified as the event with the highest risk probability by using the fuzzy comprehensive evaluation method and hierarchical analysis method.Based on the stability analysis of numerical simulation of the shield tunnel under-passing high pressure natural gas pipeline project in close proximity based on Midas/GTS NX software,the results show that the shield under-passing in close proximity will cause serious deformation of the natural gas pipeline exceeding the warning value.The risk factors initially identified by the risk evaluation method with large safety hazards are verified by numerical simulation analysis,which can more comprehensively and accurately identify the risks in the project,and the combination of the two methods can more accurately take corresponding effective reinforcement measures for the risk factors in advance.(2)In view of the instability of the natural gas pipeline,the method of sleeve tube grouting reinforcement is chosen to ensure the safety and stability of the shield structure under the high-pressure natural gas pipeline in close proximity,and the numerical calculation method is used to analyze the results,which show that the sleeve tube grouting reinforcement method can effectively suppress the disturbance deformation of the soil above the shield tunnel and thus ensure the stability of the high-pressure natural gas pipeline.(3)After compiling the field monitoring data and comparing them with the numerical simulation data,it was found that the two data were slightly different but the trend of the data analysis curve was more or less the same,thus proving the reliability of the numerical simulation results and the feasibility of the sleeve tube grouting reinforcement method.(4)The numerical simulation method was used to optimize the width and height of the sleeve pipe grouting reinforcement to reduce the reinforcement area as much as possible to ensure the safety of the gas pipeline,thus saving costs.The results show that the slurry reinforcement project can be further optimized in terms of slurry width by reducing the width of the slurry reinforcement area from 9 m to 6 m.However,due to the close distance between the shield tunnel and the gas pipeline,optimization of the slurry height is not recommended in this paper.