Stability Analysis Of Ground Surface Settlement Induced And Surrounding Rock By Shield Driving Caused In Upper-soft And Lower-hard Composite Ground

In recent years,Under the policy guidance of China’s urbanization vigorously, With the rapid development of infrastructure of the city,a large number of population to cities,traffic congestion has become a major contradiction of hindering urban development,the construction of subways is currently one of the best ways to solve traffic congestion ground.However,geological conditions of each region,hydrological conditions and the surrounding environment are vastly different,Shield excavation causing subsidences and disturbance of the Surrounding soil are obvious difference,the Large surface subsidence could cause the collapse of the soil,ground buildings collapsed, and so greater economic losses.This paper based on the engineering background of Hefei No.1subway line FanHua road to High-speed Rail station,the model of Shield excavation in upper-soft and lower-hard composite ground is model of the difference software FLAC3D. Surface subsidence the general rule are introduced in detail. Based on analysing the numerical results and experimental results, the range of ground settlement caused by Shield excavation is got to provide guidance for the construction and it has a great significance in ensuring the safety of surrounding buildings underground pipe network and construction work and reducing project cost.(1) In considering shield construction conditions, the soil layer, the tunnel face pressure, Segments, the layered soil and other factors of Contact surfaces, build a three-dimensional numerical model and simulate dynamic process of shield tunneling excavation. Contrasting with the simulation results and field measured data can know consistent trend curve, so Three-dimensional model can better simulate actual working conditions.(2)Through analysis and study,Three kinds of conditions are lining ring vault and the upper dome rock subsidence occurred. surrounding soil of in the lining ring vault settlement value is the maximum and in the vertical direction the settlement amount smaller,the farther away from the vault.(3)Simulation using finite element analysis softwarecan obtain surface subsidence displacement the range of bustling Avenue to High Speed Rail Station, shield tunneling effects in the range of lateral surface subsidence probably about20m away from the midline of tunnel under the three conditions. With the shield tunneling Longitudinal Settlement of surface is gradually increasing and Change of the value of the settlement has The maximum when shield goes by.(4)Distribution and variation of the vertical stress field of soil caused by shield construction has consistency. Maximum vertical pressure of soil located at the waist of Lining arch ring and Maximum vertical pull located at the bottom of the lining ring arch.(5)Under three kinds of construction conditions the greatest changes of horizontal displacement of soil are away from the tunnel in the vicinity of the middle8m. The maximum amount of horizontal displacement of soil is8mm. Deformation of the soil level of influence is15m away from the tunnel centerline line under different distances of shield driving.(6)By comparing the measured and simulated,surface subsidence of singlet shield tunnel midline is maximum and gradually decreases to both sides.Shield Tunnel broadly distributed in the main settlement area around the center line of the range of2D.Outside settling tank centerline about20m, the settlement value is about2mm which described the affected area of transverse centerlineroughly is about4D.