Research On Excavation Sequence Optimization Of Shallow Buried Small Clearance Three-hole Metro Tunnel

With the rapid development of China's economy,underground engineering and tunnel construction have appeared in large numbers in people's vision.In order to make better use of underground space,porous shallow-buried parallel small-clearance tunnels are increasingly appearing in tunnel construction projects.Since the following tunnel will affect the preceding tunnel,the improper construction sequence may increase the risk during the tunnel construction,and the reasonable construction sequence can effectively ensure the stability of the surrounding rock during the tunnel excavation process.At present,there are relatively few studies on tunnels with three holes and more at home and abroad,and there are few studies on the construction sequence of three holes and above.How to adopt a reasonable construction sequence to ensure the safety of tunnel construction Has attracted more and more attention.This paper takes the shallow buried three-hole small clear-distance tunnel project in the section between Qingxihe Station and Liujiayuanzi Station of Chongqing Line 6 branch line as the background,and uses three-dimensional numerical simulation software to establish a tunnel model in the background of this project,and performs its construction Numerical Simulation.By simulating the actual working conditions on site,analyzing the mechanical characteristics and displacement of surrounding rock during the construction stage,and combining the measured data on the surrounding displacement of the tunnel to verify the reliability of the numerical simulation.Furthermore,the study focuses on the different excavation sequences of the three-hole tunnel.By comparing and analyzing the changes in the stability of the intermediate rock column,the ground settlement,and the surrounding displacement of the six different excavation sequences,the three-hole shallow-buried small net Optimal excavation sequence from the tunnel.The main research contents and conclusions of this article are as follows:(1)Simulation of the actual working conditions and construction sequence of the site through numerical simulation,analysis of the mechanical signs of the intermediate rock column and the displacement of the surrounding rock during the parallel construction of its porous tunnel,and the influence of the following tunnel on the preceding tunnel is mainly concentrated on the side of the tunnel.On the wall,the backward tunnel will cause a superposition of the stress and displacement of the forward tunnel.By comparing and analyzing the actual data and simulation data of the tunnel arch settlement,the reliability of the numerical simulation in this paper is verified.(2)The numerical simulation of six different tunnel excavation sequences was conducted to analyze the stress distribution of the intermediate rock column,ground surface settlement,and displacement around the tunnel.The locations of the maximum ground settlements obtained for the six schemes vary according to the construction sequence.It can be seen from the simulation analysis of the displacement around the tunnel that the displacement deformation around the tunnel is large,and the displacement deformation around the tunnel is small after the excavation.When multiple tunnels are constructed in parallel,tunnel support should be strengthened and construction disturbances should be reduced.(3)Uses numerical simulation to analyze and compare the three aspects of surrounding rock stress,surface settlement and peripheral displacement of the six construction sequence schemes.Pros and cons.Comprehensive analysis shows that Option 2(excavating the rightline tunnel first,then the mid-line tunnel,and finally the left-line tunnel)is better in terms of surface settlement,surrounding settlement of the tunnel,and rock column force between tunnels.This scheme is the best of the six excavation sequence schemes,which can more effectively guarantee the safety of tunnel construction.