Research On The Influence Of Earth Pressure Balance Shield Tunneling Parameters And Slurry Balance Shield Tunneling Parameters On Surface Settlement In Water-rich Clay Stratum

In order to effectively control the surface subsidence and the deformation of adjacent buildings,the shield tunneling mode is often used in subway construction under waterrich clay strata.This article relies on the project of Shenyang Metro Line 4 Wanghuajie Station-Laodonglu Station Intersection Tunnel,Laodonglu Station-Wanghuatun Station Intersection Tunnel.The tunnels pass through the stratum of water-rich silty clay,among which the particles with particle size ≤10μm account for 61.23%.The tunnels pass through many old buildings with shallow foundations,and it is necessary to strictly control the disturbance of the ground and the impact on buildings caused by shield tunneling.The dual-mode shield machine is used in this project.The shield machine can freely switch between the earth pressure balance mode and the slurry balance mode,that gives full play to the advantages of shield tunneling with strong stratum adaptability,high tunneling efficiency and good stratum settlement control effect.In this paper,by means of "document review,experimental research,numerical simulation and field measurement",the starting point is to control the surface subsidence caused by shield tunneling and ensure the safety of adjacent old buildings.This paper mainly studies and analyzes the selection of shield tunneling mode under water-rich silty clay stratum,the influence of mud infiltration and mud film quality of shield tunneling in slurry balance mode on surface subsidence,and the influence of key parameters of shield tunneling in earth pressure balance mode on surface subsidence.The main research contents are as follows:(1)In this paper,a hierarchical structure model for shield tunneling mode selection is established,which considering factors such as shield tunneling characteristics,environmental adaptability,excavation feasibility,economic rationality,and environmental protection.Through the quantitative analysis of the influence of hierarchical structure model factors,the excavation sections of the slurry balance mode and the earth pressure balance mode are divided.In this paper,a test section of shield tunneling is set up to study the key technology of conversion between slurry balance mode and soil pressure balance mode of dual-mode shield.(2)In this paper,the self-made mud permeation column is used to study the effect of mud permeation film formation in slurry balance shield tunneling in water-rich strata with high clay content in Shenyang,and the law of mud permeation and mud film formation in excavation face during slurry balance shield tunneling is analyzed.The research shows that the slurry permeability and slurry film-forming quality of the excavation face are affected by the support pressure and slurry ratio,and the slurry ratio most suitable for the formation is different under different support pressures.The slurry ratio most suitable for the burial depth and engineering geological conditions of this project is 100 g / L of clay and clear water,5 % of bentonite and 0.03 % of CMC.(3)According to the results of slurry penetration test,the finite difference software is used to establish a numerical analysis model to simulate the process of slurry infiltration and mud film formation in the forward soil during slurry shield tunneling.The effects of slurry support pressure,mud film permeability coefficient,mud film thickness and mud film formation time on surface settlement and soil disturbance are studied.The research shows that the ground settlement of shield tunneling is related to the mud film parameters such as the thickness,permeability coefficient and film forming time of the mud film.The thicker the mud film,the smaller the maximum surface settlement;reducing the permeability coefficient of mud film can effectively reduce the surface settlement caused by shield tunneling;accelerating the formation of mud film at the excavation face helps to reduce ground settlement.(4)Based on FLAC 3D finite difference software,a numerical analysis model is established to simulate the tunneling process of earth pressure balance shield.The influence of shield grouting pressure,grouting thickness and synchronous grouting pressure on ground settlement is studied.The results show that the increase of soil bin pressure,grouting pressure and grouting layer thickness can reduce the influence of shield construction on ground settlement.According to the research results,the key parameters suitable for the shield tunneling of earth pressure balance mode are proposed.(5)In view of the conditions of shield tunneling through many old buildings with shallow foundation,protective measures such as adding grouting holes on B-type segments and radial grouting are proposed.The numerical simulation method is used to study the influence of slurry balance mode and soil pressure balance mode on the settlement of shield tunneling under buildings,and the settlement control effect of shield tunneling under different tunneling modes is studied combined with field measured data.