Research On The Influence And Control Of The Upper River Channel Excavation On The Existing Subway Tunne

At present,urban rail transit has become an important part of urban public transport,which has the advantages of large volume,fast speed,less occupation of land resources and so on.It can effectively alleviate the problems of dense population,housing shortage,traffic congestion and other problems in the process of urbanization.However,with the construction of a large number of urban subways,more and more foundation pit projects are located above the existing subway tunnels.This situation will have a great adverse impact on the existing tunnels,such as tunnel deformation,cracking and so on,affecting the safety of the tunnels.In view of the above problems,this thesis,based on the Longji River excavation project in Jinan City,adopts the method of combining numerical simulation,theoretical analysis and field monitoring to study the disturbance influence mechanism of the upper river excavation on the existing subway tunnel,reveals the disturbance influence rule of different factors on the subway tunnel,and puts forward the theoretical prediction method of the disturbance influence of the upper river excavation on the existing tunnel.The corresponding engineering suggestions and measures are given.Finally,combined with the practical application of the project to ensure the safety of the subway tunnel during construction.The main research content of this thesis includes the following three aspects:1.By using the finite difference software FLAC3 D,25 kinds of comparison schemes were designed to carry out numerical simulation and comparison study,considering 5 major influencing factors,such as the relative distance between different rivers and tunnels,the width of river excavation,the depth of tunnel excavation,the thickness of grouting reinforcement and the range of grouting reinforcement,and to analyze the disturbance influence law of upper river excavation on strata and tunnels under different working conditions.The sensitivity evaluation index of the influencing factors of river uplift and displacement is established,and the sensitivity of the five influencing factors is analyzed,and the corresponding engineering suggestions are given based on the engineering practice.2.By analyzing the disturbance influence mechanism of river excavation on stratum soil and tunnel,a mechanical analysis model of the disturbance influence of upper river excavation on existing tunnel was established.Based on Mindlin formula,analytical calculation formulas of the disturbance stress of river bottom unloading and the disturbance stress of side wall unloading were derived.Furthermore,based on the conventional method,the theoretical prediction and analysis method of the influence of upper channel excavation on the existing tunnel disturbance is put forward.The perturbation effect of different parameters on the internal forces of existing tunnels is revealed through the analysis of numerical examples.3.Select a typical part of Longji River channel excavation project to carry out a threedimensional numerical simulation study on the influence of box culvert excavation on the existing subway tunnel disturbance under two conditions of grouting and non-grouting,and verify the deformation control effect of grouting reinforcement on the existing tunnel and stratum soil.Further,the grouting method is used to reinforce the foundation on site,the tunnel structure deformation during the whole process of foundation pit excavation is monitored in situ,and the numerical simulation results are compared and analyzed,so as to ensure the safety of the subway tunnel during construction,and verify the correctness of the research method and the accuracy of the research conclusion.