| In order to meet the needs of different engineering conditions,the parallel construction of shield tunnels and shallow buried tunnel with small net distance has been increasing recently in the existing urban rail transit section tunnel construction process.Because shield tunneling method and shallow mining method have different disturbance forms and influence ranges on surrounding rock,it is more and more difficult and risky to construct shield tunnels and mining tunnels with small clear distance.The existing design specifications only stipulate the minimum net distance between parallel tunnels,but in practical engineering,the net distance between two tunnels is restricted by objective conditions,which may be much smaller than the specifications.Therefore,it is of great practical significance to analyze the effect of late tunnels on deformation of early tunnel in three small net distance tunnels,explore the minimum net distance between the tunnels that need to take reinforcement measures as well as study the reinforcement effect.This paper is based on the tunnel construction in small net distance in Jinan Rail Transit Line R3.In order to reveal the law of the influence of the late tunnels construction on the deformation of the early tunnel,and analyze whether small clearance tunnels need to be reinforced,the deformation of early mining tunnel(CD method)when double-line shield tunneling under different net distance conditions is simulated by using Midas GTS software and the simulation results are compared with the small distance tunnel safety distance discrimination criteria.At the same time,the working conditions exceeding the control value are reinforced and numerically simulated to analyze the reinforcement effect.Then the on-site monitoring data is analyzed and compared with the simulation results.The main contents and results are as follows:Firstly,MIDAS/GTS software is used to establish the two-dimensional finite element model of the tunnels.The problem of three tunnels construction under different tunnel clearance conditions(1.2D,1.0D,0.8D,0.6D,0.4D,D is the shield tunnel diameter)is analyzed.The analysis results show that when the tunnel net distance decreases to 0.8D,the plastic zone of the left and right shield tunnels overlaps with that of the first shallow buried tunnel.When the tunnel net distance decreases to 0.6D,the vault settlement of the shallowburied tunnel is approaching the control value.It is necessary to take some reinforcement measures when the net distance is less than 0.8D.Secondly,based on the analysis of deformation control measures of small clear distance tunnel,two reinforcement methods suitable for this project are put forward,namely curtain grouting method and bored cast-in-place pile method.By using MIDAS/GTS software to analyze the two reinforcement methods,it can be concluded that drilling cast-in-place piles can better control the deformation and displacement of the shallow buried tunnel.After drilling cast-in-place piles,although the deformation of the shallow buried tunnel increases slightly with the decrease of net distance of tunnels,it does not change much,far less than its deformation control value,and the plastic zone no longer overlaps,which makes the safe construction of ultra-small net distance possible.Finally,the vertical and horizontal deformations of shallow buried tunnel are analyzed by field monitoring data.The analysis results show that before the shield reaches a section of the shallow buried tunnel,the thrust of the shield will cause the vault to rise,the inverted arch to sink,and the clearance to converge.After the shield tunneling,the weakening effect on the surrounding rock and the stress release effect will cause the vault to settle,the inverted arch to rise,and the clearance will expand.Then the monitoring data is compared with the numerical simulation data.It shows that although the data is not the same,the values are basically close,and the errors are not very large,the influence of the late shields on the first shallow buried tunnel is basically the same,as well as the numerical simulation method can truly reflect the construction of the project. |
