Deformation Law And Control Strategy Of The Subgrade Under Shield Crossing High Railway

With the booming economy of China,the rail transit network will become more and more perfect.Shield method has become one of the most important methods of tunnel excavation because of its advantages of small impact on the environment.In the process of shield tunnel construction,it is inevitable to encounter engineering problems such as passing through existing structures,which will cause uneven settlement of structures and endanger personnel safety.Therefore,before shield construction,it is necessary to analyze the soil deformation and put forward corresponding reinforcement measures to ensure the shield to penetrate the structures safely.Based on the case study of Huaian east station shield underpass high-speed railway roadbed project,this paper studies the influence of shield underpass high-speed railway roadbed on railway track,roadbed and ground surface in silty sand stratum.Through theoretical and numerical simulation analysis of ground settlement during shield construction,the maximum ground settlement after double tunnel construction is calculated.Based on this,the reinforcement measures are proposed and the reinforcement scope is determined.Moreover,real monitoring data are compared and analyzed to confirm the reliability of the reinforcement.The results are as follows:(1)Using peck superposition principle to calculate the surface settlement,the maximum theoretical settlement is 29 mm.(2)Through numerical simulation analysis,under the condition of undisturbed soil layer,the surface,roadbed,and the maximum settlement value of the track,all appeared in the middle of the two tunnels,which conforms to the superposition law of peck formula.When no reinforcement measures are taken,the maximum settlement of surface is 28.94 mm,the maximum settlement of roadbed is 24.5mm,and the maximum settlement of rail is 25.12mm;under the actual engineering geological conditions(CFG pile),the maximum settlement of surface is 28.94 mm The large settlement is 22.34 mm,the maximum settlement of roadbed is 18.83 mm,and the maximum settlement of rail is 19.24 mm,which indicates that CFG pile has a certain role in reducing ground settlement.(3)The settlement of point a(the intersection between the two tunnels and the roadbed)with the excavation distance can be roughly divided into four stages: before the shield arrives,during the shield crossing,after the Shield Crossing and during the excavation of the right line.Due to the characteristics of silt stratum,the settlement caused by consolidation creep of soil is small,which is mainly caused by the disturbance of silt stratum caused by right tunnel excavation.(4)According to the economy and safety of the actual project,grouting reinforcement within 2m outside the tunnel is the best reinforcement range.The results show that the grouting reinforcement measures can effectively restrain the deformation of the soil layer as it penetrates the roadbed.The settlement at A point of left tunnel excavation is decreased by about 71%,and that at A point of right tunnel excavation is decreased by about 76%.The grouting reinforcement measures have a good inhibiting effect on the settlement at the third and fourth stage of the shield passing through the high-speed railway roadbed.Through the calculation of applying train load,it can be seen that the settlement of stratum,roadbed and rail has almost no increase after applying train load,which indicates that the reinforcement effect is good and meets the requirements of train operation.(5)According to the analysis of the actual monitoring data,after the completion of the two tunnels,the maximum ground settlement is 5.94 mm,the maximum roadbed settlement is 5.32 mm,the maximum rail settlement is 5.89 mm,and the maximum settlement occurs near the middle of the two tunnels.The settlement before shield underpass accounts for 26%of the total settlement,59% when shield underpass,11% when shield shell comes out of segment,and 5.9% after shield excavation.