Study On Disturbance Effects Of Shield Tunnel Crossing Railway Group In Operation And Active Protection

With the rapid development of urban rail transit construction in China,the problem of tunnel crossing buildings has received more and more attention.The railways and their safe operation have high deformation requirements.In the process of shield tunnel crossing the operating railway,the excavation unloading,stress release,soil disturbance and stratum loss have different effects on the railway subgrade,railway bridge and rail,which leads to the safety of train operation.Especially for the railway group project in which the tunnel crosses the railway subgrade and the high-speed railway bridge adjacent to each other,it is the key and difficult point in the project.In order to ensure the deformation of the railway group structure to meet the requirements of safe operation of the train,it is of great significance to study the deformation law and active protection measures of the operating railway group in the tunneling process.Based on the project of tunnel crossing the Jiaoji Railway and the Qingdao-Jinan passenger railway of the Jinan Metro R3 line first phase project,a 3D numerical model is established and the deformation of subgrade,rail and bridge of railway group and the force law of pile during the shield excavation process is studied.Finally,effective active protection measures are proposed.The main research contents and results are as follows:(1)Based on the finite element numerical simulation method,the 3D construction simulation analysis of the R3 line shield tunnel crossing the railway subgrade and railway bridge was carried out.Through the simulation comparison of the construction load combination scheme,the results show that the change of grouting pressure has the greatest impact on railway subgrade and railway bridge;through the simulation analysis of the optimal construction load combination scheme,the results show that the settlement value of the railway subgrade and the Y-direction and Z-direction displacement values of the railway pier exceed the safety alarm value after the completion of the construction of the double-line shield tunnel without the reinforcement measures;through the simulation analysis of the construction process of the shield tunnel through the railway group,the results show that the railway subgrade and the railway bridge have little influence on each other.(2)This paper summarizes the similar construction cases in China.Active protective measures suitable for the project were initially selected,that is,the railway subgrade is pre-treated with sleeve valve grouting reinforcement measures,and the bored pile isolation measures are taken for the railway bridge section.At the same time,three types of bored piles Ф0.6m@0.8m,Ф0.8m@1.0m and Ф1.0m@1.2m were compared.The simulation results show that,the grouting reinforcement measure for the soil under the railway subgrade and the active protective measure of the isolation piles between the 32# pier and the shield tunnel have obvious effects on the deformation control of the railway structure;Comparing the calculation results of the three isolation pile reinforcement schemes,the difference between the deformation of the surface,railway pier,subgrade and rail under the Ф0.8m@1.0m isolation pile scheme and the Ф1.0m@1.2m isolation pile scheme is very small.(3)Combined with the on-site shield tunneling construction step,the measured data was collated and analyzed.The results show that the deformation law of railway subgrade and rail and railway pier is basically consistent with the simulation results.However,due to the two shutdowns in the construction of the right-line shield tunnel,the deformation of railway subgrade and rail is over-limit.According to the research results and combined with the problems in construction,engineering safety technical measures are proposed for the construction of shield tunnels crossing railway lines.