Study On The Influence Of Stacked Shield Tunnel Construction On Ground Deformation And Mechanical Performance Of Lining Structure

In recent years,with the vigorous development of urban subway track engineering,due to the influence of adjacent underground structures(structures),subway tunnels usually can only be arranged by overlapping tunnels at the intersection of two track lines or part of a line.planning.Since the stacked up and down tunnels will have disturbance and superposition effects on themselves and the surrounding environment after the construction of the stacked up and down tunnels,the surrounding soil layers and the structure of the pre-formed tunnel will have complex forces,relatively large deformations,and high construction safety risks.Therefore,this paper relies on a certain actual stack Research on shield tunnel engineering.The project has the characteristics of small tunnel clear distance,of which the minimum clear distance is only 4.48 m,the geological conditions are poor,and the spatial relationship is complicated.This paper uses Midas GTS NX finite element calculation software to carry out three-dimensional modeling and analysis of the project.The construction sequence of the stacked shield tunnel,the influence of the construction of the later up tunnel on the surface settlement and the mechanical performance of the lining structure of the first down tunnel are studied..The main research work and conclusions are as follows:(1)Through the spatial position relationship of the subway tunnel and the classification of the construction types of adjacent tunnels,the dynamic analysis of the deformation of the first tunnel during the construction of the superimposed tunnel is explained.Based on elastic mechanics and soil mechanics,the mechanical characteristics and deformation mechanism of stacked tunnels are systematically summarized.Organize the load and torque formulas during the tunneling process of the shield machine.(2)Combining with the important and difficult problems of small distance between the upper and lower tunnels and poor geological conditions in an actual project,Midas GTS NX finite element simulation software is used to model the stacked shield tunnel,and the modeling process is discussed in detail.The whole process of calculation assumptions,grid division,calculation parameters and shield construction simulation.(3)Through the method of numerical simulation analysis,the two construction sequences of "up and then down" and "down and up" of the stacked shield tunnel are compared and selected,and the ground settlement,the displacement of the surrounding soil and the internal force of the first tunnel segment are analyzed.And deformation.Through comparison,it is concluded that the construction sequence of "first down and then up" is better than "first up and then down".(4)For the tunnels with a clear distance of 4.48 m,6.55 m completely overlapped section and a clear distance of 6.68 m oblique overlapped section tunnels,a three-dimensional calculation model was established for the overlapped sections of three typical working conditions,and different spacings were analyzed.The impact of stacked shield tunnel construction on ground deformation and the mechanical performance of the lining of the first-built tunnel.Through analysis,it is concluded that the construction of stacked shield tunnels will lead to the superposition of surface settlement,and the superposition deformation is relatively large,but the change in the width of the settlement trough is small;when the upward tunnel construction is built later to the first downward tunnel construction,the studied section When the segments are affected by the segment,the segments of the first-built tunnel are subject to greater stress and deformation;the smaller the upper and lower spacing of the stacked shield tunnel,the greater the impact of the construction of the later tunnel on the surface settlement and the deformation of the first-built tunnel.(5)The on-site monitoring results are compared with the numerical simulation calculation results,and the analysis shows that the deformation laws of the two are consistent.The measured value is slightly larger than the simulated value,but the error is within the controllable range.Verify the feasibility of Midas GTS NX finite element calculation software for engineering modeling analysis.