Study On The Impact And Control Measures Of Shield Tunneling On Existing Stations And Lines

During shield tunneling construction of urban subway tunnels,it is inevitable to pass through existing underground pipelines,building foundations,subway stations,and related underground structures(structures).Tunnel shield tunneling construction can cause disturbance to the soil layer,thereby affecting the stability of its related structures.In severe cases,it can cause functional damage to existing structures,leading to accidents.Once an accident occurs,it not only leads to the stagnation of subway construction,causing economic losses,but also has a significant negative impact on the city.Based on the project background that Chengdu Metro Line 17 is going to underpass the existing Metro Line 2 and its Renmin Park Station,this paper conducts preliminary analysis and research on the possible safety risks from both theoretical analysis and numerical simulation,so as to predict the engineering difficulty and existing risk level in the process of shield tunneling in advance,and provide some decision-making reference for the formal construction.The main research work and related research results are as follows:(1)Based on the analysis of stress distribution,the stress redistribution status between the station under the tunnel of Line 17 and the existing line section was summarized.And through calculation,it is shown that the vertical stress above the left line tunnel is about334KN/m~2,and the vertical stress above the right line tunnel is about 141KN/m~2.The impact of the left line tunnel excavation on the surface and existing lines is greater than the impact of the right line tunnel excavation on the surface and stations.(2)Establish a model for the shield tunneling of Line 17 through existing stations and lines through Midas GTS and conduct numerical simulation calculations.The calculation results indicate that the shield tunneling underneath the station and the existing line will have a destructive impact.Its weak point is located at the connection between the existing station and the line,and the maximum tensile stress it receives is 2.7Mpa,exceeding the design value of its tensile strength of 1.57 Mpa.The inclination rate of the existing line is 0.17‰,and the inclination rate of the station is 0.3‰.The uneven settlement trend of the station is higher than that of the existing line.By conducting numerical simulation calculations on the settlement of interlayer soil caused by shield tunneling through existing stations and lines,it can be concluded that under certain physical parameters of the existing structure,the existence of the existing structure can reduce the settlement of the interlayer soil layer.The extent of settlement reduction is positively correlated with the distance between the soil layer and the existing structure,and the range of reduction is also positively correlated with the width of the existing structure.Numerical simulation calculation of surface settlement can effectively reduce surface settlement caused by shield tunneling due to the presence of existing stations and lines.(3)On the basis of summarizing the excavation parameters,grouting reinforcement measures,and monitoring and control measures in the construction of shield tunneling,numerical simulation calculations were conducted on the reinforced strata.The results showed that the reinforcement measures taken can effectively reduce the maximum tensile stress on the station and line,with a maximum tensile stress of 1.47 Mpa,which does not exceed the design value of 1.57 Mpa for its tensile strength,and can ensure the safety of construction to a certain extent.The settlement of the interlayer soil on the left and right lines has significantly decreased.The maximum settlement of the interlayer soil within the reinforcement range has decreased by 86% and 70%,respectively.The difference in settlement of the interlayer soil on the left and right lines has also decreased compared to before reinforcement,with a decrease of 76%.Grouting reinforcement of the soil layer can effectively reduce the uneven settlement of the interlayer soil.The inclination rate of the existing line is 0.08‰,and the inclination rate of the station floor is 0.1‰.The prevention and control measures of grouting reinforcement for the soil layer can ensure the overall stability of its structure.