Study On Ground Deformation Caused By Shield Tunnel Underneath Existed Tunnel

China's urban rail transit construction has not only developed rapidly,but has also achieved efficient and rapid development.The excavation and construction of urban subway buildings and tunnels is an important technical means to relieve the pressure of urban traffic.This paper takes the shield construction of Tianmushan Tunnel in Hangzhou,Zhejiang Province as the engineering background,and studies and discusses the influence of shield tunnel construction methods on the settlement and deformation of the ground and its laws.These studies make the prediction and protection of ground subsidence caused by similar subway tunnels during construction.This is of great significance for the future research on the shield construction of underground tunnels on the ground deformation and the settlement law of existed tunnels.The main research includes the following aspects:(1)The factors of surface deformation that may be caused by passing under existing tunnels during shield construction are analyzed,and the degree of influence on existing tunnels during shield construction is also studied.The study found that the buried depth of the tunnel,the surrounding rock grade,and the intersection angle between the two tunnels are all related to the ground settlement,and there are many uncertain factors in the actual construction.(2)Based on the empirical formula of stratum settlement——peck formula,combined with the existing monitoring data of Hangzhou area,the range of surface settlement is summarized.Compare it with the results calculated by the peck formula,so as to summarize how to use the peck formula to predict settlement calculation in this area.Then,based on the physical and mechanical parameters of the soil in Hangzhou,through theoretical derivation,the prediction formula of surface settlement is given.(3)Based on the numerical analysis software MIDAS,the influence law of the soil settlement caused by the construction of the shield tunnel is fully considered when the soil parameters change regularly.Through the control variable method,only the assignment of the soil parameters to be studied is changed,and the other soil parameters are kept unchanged,so as to obtain the influence of different soil parameters on the ground subsidence when changing.(4)Taking the shield excavation section of the Tianmushan Tunnel in Hangzhou as the background,based on the commonly used finite element analysis software MIDAS GTS/NX,the working conditions of the new tunnel and the existing tunnel at different positions are not simulated.Then it analyzes the influence of shield method construction on the settlement and deformation of the existing tunnel in the soil surface and the soil layer during the construction of the subway tunnel.