| With the continuous improvement of China’s comprehensive national strength and the acceleration of urbanization process,which inevitably brings increasingly busy and congested urban traffic.Major cities have adopted the method of building urban rail transit to alleviate traffic congestion.Due to the large number of surface buildings in the city,most of the projects are constructed by shallow buried excavation in the process of building the railway loop.When the tunnel passes through the existing overpass bridge piles,the excavation construction will inevitably destroy the initial equilibrium state of the surrounding rock,and the strata will also undergo stress redistribution within a certain range,which may cause the ground to settle or collapse.The interaction between piles and soil will lead to uneven settlement and deformation of the overpass,which will lead to the reduction of bearing capacity and cracking,reduce the service life,further affect the normal use of the highway,and even pose a threat to the safety of people’s lives and property.Therefore,it is of great significance to study the influence on the existing overpass and strata during tunnel excavation to guide the safe construction of the tunnel.Based on the bridge project of Jinshan tunnel crossing Zhaojiaxi overpass road in Yubei district of C hongqing city,this paper analyzes the influence of different excavation methods on stratum and pile foundation of existing overpass when constructing tunnel in complex stratum by using the method of field measurement,theoretical analysis and finite element numerical simulation calculation,and summarizes the deformation law of corresponding stratum and pile foundation.The main research contents are as follows:(1)The data and data of stratum settlement and bridge pile foundation deformation caused by typical newly-built tunnels in China in recent years are collected,and on the basis of statistical analysis,the laws a nd mechanical characteristics of stratum settlement and bridge pile foundation settlement caused by newly-built tunnel construction are summarized.(2)The finite element software is used to simulate and analyze different construction environments,and the tunnel vault settlement,peripheral convergence,surface settlement,pile foundation displacement and pile foundation internal force changes under different construction environments are analyzed in detail.Therefore,the influence of different tunnel construction methods on the ground surface and pile foundation under different rock dip angles,the influence of different tunnel construction methods on the ground surface and pile foundation under different buried depths and the influence of different tunne l construction methods on pile foundation at different positions in the construction process of shallow buried tunnels are obtained.From the above research,we can know that different tunnel construction methods have different influences on the stratum and pile foundation.On the whole,the influence on the stratum and pile foundation by adopting the middle partition wall(C(D)method is weaker than that by adopting the step method and temporary inverted arch.Therefore,it is suggested that the tunnel construction method with shorter footage or stronger supporting ability can be adopted in the poor surrounding rock sections to ensure the safety and smooth construction process.(3)Relying on the actual project of underpass overpass,that is,underpass Zhaojiaxi overpass project of Jinshan tunnel in Yubei district of Chongqing city,the section project with similar geological conditions to the numerical simulation is selected,and the method of comparing the on-site actual monitoring data with the numerical simulation results is adopted to find that the surface settlement curve is basically consistent,further verifying the correctness and rationality of the numerical simulation results and parameter selection.Therefore,it provides reference value for the construction of similar projects in the future. |
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