Numerical Simulation Of Surface Subsidence Caused By Large-diameter Shield Tunnel Crossed Underneath The Main Canal Of South-to-North Water Diversion Project

Surface settlement is one of the geological disasters caused by the shield tunneling during construction.If not controlled,it can cause serious consequences,e.g.,property damage and environmental damage.In severe cases,it will affect the surrounding buildings and people lives.The South-to-North Water Diversion Project is a strategic project in China.The mid-line project is derived from the Danjiangkou Reservoir,which benefits Henan,Hebei,Beijing,and Tianjin.The damage of the main channel structure can affect the function of the project and cause serious consequences.This thesis takes the tunnel section of the South-to-North Water Diversion Project under the shield construction of the Yuji Railway Project as the research object.The mechanism of influence of shield construction on surrounding soil is firstly discussed.Secondly,the thesis systematically study on surface settlement caused by shield construction.Based on the research results,control measures for surface settlement are proposed,which effectively reduce surface settlement caused by shield construction.The conclusions of this paper and the construction measures adopted by the project have certain reference value for similar projects.The main contents of the thesis are as follows:(1)A numerical calculation model is established by using FLAC3 D finite difference software.By combining engineering data and shield-related parameters,impact of simulated shield construction on main canal structure is analyzed.Experimental results show that the results obtained by numerical simulation are close to the results obtained by empirical formula,which proves the accuracy of numerical simulation method.Experiments results also show that the numerical simulation results are consistent with the results obtained by theoretical analysis.Hence numerical simulation method has reference value in the study of ground deformation caused by shield construction.(2)There is obvious surface settlement in the area within 1 to 2 times the shield diameter far in front of the shield tunneling.The tunneling parameters and the soil parameters have a significant effect on the surface settlement.In the horizontal surface settlement,the maximum settlement appears at the axis of the tunnel,with the settlement gradually decreasing to both sides and the influence range is concentrated within twice the tunnel diameter.The longitudinal surface settlement curve shows that the tunneling parameters do not affect the distribution type of the surface subsidence along the longitudinal direction,but affect the distribution parameters.(3)By using single factor method,the thesis studies on the influence of calculation parameters on surface settlement.As the advance rate increases,the maximum surface settlement decreases.Increasing the thrust of the excavation surface within a certain range helps reduce the surface settlement.Considering the construction control standards and economy,the thrust of the excavation can be chosen as 1.25 times more than the theoretical value.The larger the elastic modulus of the soil and the larger the internal friction angle,the stronger the shear resistance of the soil and the smaller the maximum surface settlement.(4)By using factor analysis method,the average sensitivity of the surface settlement to different factors is analyzed.The results show that the surface settlement is most sensitive to the friction angle in the soil,and the degree of sensitivity of the friction angle in the soil,the elastic modulus of the soil,advance rate,thrust of the excavation surface and grouting elastic modulus decrease in turn.