Numerical Simulation Analysis Of Shield Tunnel Under A Composite High-speed Railway Bridge Pile Foundation And Railway Subgrade

Under the background of the new normal of China’s economic development,the pace of investment in infrastructure construction has continued to accelerate.As a part of infrastructure investment,subway construction has also been developed rapidly.However,it is inevitable that there will be a crossover between the new subway interval tunnel and existing railway line in the process of urban subway design and construction.Metro tunnels are often constructed in the shield method.The shield tunneling method is widely used in the construction of urban subway tunnels because of its small impact on the surrounding environment and high degree of mechanization.However,this method will still affect the soil around the tunnel and cause disturbances formation loss and soil stress field changes.These changes in the soil disturbed by the construction around the tunnel cause uneven settlement of the strata in a certain extent,the uneven settlement will be transmitted to the existing bridge structure and subgrade structure through the rock and soil media,so as to cause a certain deformations in the existing subgrade and bridge structure.When these distortions are large,there is a potential risk for the safety operation of existing lines.To ensure the safe operation of the existing railway lines during the tunneling process of the shield tunnel.Therefore,it is of great practical significance to study the effect of shield tunnel under-construction on the deformation of the existing high-speed railway bridge structure and the general railroad base structure.The paper integrate a actual engineering projects,building a three-dimensional solid model by using the finite element software GTS-NX.According to the actual construction conditions,numerical simulation analysis is conducted on the deformation law of the shield tunnel underpassing existing high-speed railway bridge pile foundations and general railroad bases.The main research results include the following aspects(1)This paper summarizes the research status of the effect of shield tunneling at home and abroad on the deformation of strata and adjacent pile foundations.It also summarizes the application cases of the shield under-construction.Then,discussing the stratum from the mechanics of the shield tunnel construction.Based on the basic principles of deformation and pile deformation.Finally,defining subgrade settlement and deformation of bridge structures were determined based on related specifications,literature,and engineering experience.(2)Analyzing the settlement of roadbed during the tunneling process of shield tunnel.The excavation of the shield tunnel is accompanied by the expansion of the surface settlement tank.During the excavation and penetration of the left-line tunnel,the roadbed settlement tank is located above the center line of the left-line tunnel.As the tunnel of the right line is cut open,the subgrade settlement gradually moves toward the right tunnel.The largest settlement tank is located above the center line of the two tunnels and the maximum settlement tank conforms to the Peck curve law,which has obvious superposition effect.The settlement value of the subgrade measurement point is related to the construction location of the shield tunnel.The analysis results show that the maximum settlement value of the railway subgrade is less than the 10 mm control requirement specified in the standard,and no reinforcement measures are required for the subgrade.(3)Analyzing the deformation of piers and pile foundations caused by shield tunnels passing through existing bridge structures.The deformation value of bridge pier with existing bridge structure exceeds the 2mm control requirement of ballastless track specified in Technical Regulations for Highway and Municipal Engineering Underpass High-speed Railway(TB 10182-2017)under the condition of no protection measures.Therefore,corresponding protective measures must be taken for the existing bridge structure to ensure the safe operation of the train.(4)Analyzing the influence of two different grouting reinforcement ranges on the deformation of bridge piers in the in-hole radial grouting protection measures for existing bridge structures,as well as comparing the settlement and lateral displacement changes of existing bridge pile foundations under the two different grouting ranges.The analysis results show that the expansion of the radial grouting area in the tunnel can effectively reduce the impact of shield tunnel construction on the existing bridge structure.When the grouting range is 1D tunnel diameter,the tunnel construction has little effect on the existing bridge structure.