Study On The Stability Of Excavation Face Of Shield Tunnel And The Sensitivity Of Influencing Factors Affected By Cutter Opening Ratio

The shield method is widely used because of its advantages of fast driving speed,high construction efficiency,and ability to cope with limited space.During the construction process,the control of the shield tunneling parameters plays a key role in the stability of the excavation surface,and the reasonable choice of the cutter head opening ratio is the premise to ensure the safe and stable tunneling of the shield machine.At present,the cutterhead aperture ratio has not systematically and comprehensively studied the stability of shield excavation face and the stability of shield system.Based on this,this paper takes the Qinghai-Nanjing Metro Line 3 of Guangxi as the research background,through theoretical analysis,model test,numerical simulation and other research methods to carry out the study of the influence of the cutterhead opening ratio on the stability of the excavation surface,and the The sensitivity of each influencing factor was studied using sedimentation as an indicator.The main research contents and results are as follows:(1)The project’s engineering background and geological and hydrological conditions are studied and analyzed.According to the similarity theory,geotechnical materials with similar properties to the original soil are obtained through laboratory tests.Considering the influence of the cutter head opening ratio on the force of the shield,simplify the analysis of the force situation and modify the theoretical formula of the shield thrust and cutter head torque to provide support for subsequent tests and numerical calculations.(2)Using the self-designed mud water shield tunneling system,the three test cutters with opening ratios of 55%,38% and 21% were designed to carry out indoor model tests of shield tunneling to obtain surface settlement,earth pressure,mud pressure and shield Change the thrust and torque of the structure to obtain the limit support ratio to ensure the stability of the excavation face.(3)Using FLAC3 D finite difference software to simulate the shield tunneling process with different cutter head opening ratios,by gradually reducing the grouting pressure,the ultimate support ratio of the excavation surface and the changes in formation settlement,mud pressure,earth pressure and cutter head deformation are obtained Regularity,and comparative verification analysis with test results.(4)Based on the principle of orthogonal experiment,a numerical simulation method was used to conduct a global sensitivity study on the factors influencing the stability of the excavation face.As well as the sensitivity of influencing factors such as grouting pressure,it was found that the internal friction angle and propulsion speed have the most significant influence on the settlement index.The remaining influencing factors are also relatively sensitive,but the degree of influence is basically the same,which cannot be ignored during the construction process.