Analysis On The Mechanical Effect Of Metro Tunnel Construction Of Chongqing North Station With Zero Distance Stereo Crossing

ABSTRACT:More and more urban traffic hub project composed of urban subway station and high-speed railway station is established at home and abroad,but it is often used in the pattern of unified planning and unified construction,and the construction method is often used for open cut method during construction.In this project,two new subway stations were built by undermining method,the two new stations and the existing high speed railway station and the subway station of line No.3 forms a crossing interchange station,which is rare in China and abroad.The surrounding environment is very sensitive to the deformation and subsidence caused by the disturbance,especially the new subway station consisted of two large cross section tunnel crossing by zero distance,and the crossing tunnel is under the existing high-speed railway station and underground parking lot.The distance between the top of the large span flat tunnel of line ten and the existing pile foundation is only 2.6m,and the risk level is 1,so it is difficult to guarantee the safety of existing structures and new tunnels.This paper aims at the above problems,the methods of theoretical analysis,numerical simulation,literature survey and field monitoring are combined,the stress and deformation of the crossing tunnel construction process are analyzed,and the construction parameters are optimized.So that we can achieve the purpose of safety construction of crossing tunnel of Chongqing North Railway Station.The main research contents are as follows:(1)Study on the selection of construction method for shallow buried large span Metro Station.In this paper,through the investigation and analysis,summed up the domestic and foreign construction method of large span flat section tunnel.Based on the finite element model MIDAS-GTS,this paper compares and analyzes the mechanical indexes of the column hole method,the center drift excavation method and the side drift excavation method.And combined with the weight decision analysis method,the optimal construction method is determined.(2)Study on mechanical behavior and influencing factors of large span flat tunnel.According to the selected method,the three-dimensional numerical simulation of the construction process of large span flat tunnel in D area is carried out.The change rule of the lining stress,the surface settlement,and the vertical deformation and lateral displacement of the existing underground parking lot are analyzed and summarized.By adjusting model,this paper study on the tunnel excavation order,liner construction length,center hole lining construction time,length of dismantling support.Finally,the reasonable construction parameters are determined to protect the existing underground structure.(3)Deformation and force analysis of large section crossing tunnel and optimization of support parameters.Based on theoretical analysis,we establish the simulation model of the construction of the loop line and line ten crossing tunnel,study the law of force and deformation in the whole construction process,and determine the influence range of the loop line.According to the construction requirements,the initial support parameters are optimized.Comparison of displacement,stress,safety factor,it is found that the best supporting scheme is to make the double layer initial support,thicken the base plate of No.10 line and reinforce surrounding rock around the side wall.(4)Deformation prediction control and feedback analysis of crossing tunnel construction.Using the method of combining numerical analysis with displacement distribution control method,we have set up the step by step control standard for each stage of crossing tunnel construction.Through field monitoring test,the process control is realized by comparing the step by step control standard with the measured data.And it successfully ensures that the deformation of the points in the control of the security range.Based on the monitoring data,the paper analyzes the long term monitoring values of building settlement,crown settlement and horizontal convergence,and summaries the deformation law of each part.