Research On Effects Of Relative Position Changes Of Shield Tunneling In Overlapping Tunnels

With the increasing density of urban subway lines,the construction of overlapping shield tunnels is becoming more and more common.The construction of overlapping tunnels belongs to adjacent construction,and there are some interactions between two tunnels.Also,the influence on surrounding strata is different from construction of single tunnel.The sequence of the construction,the excavation methods and the relative position of overlapping tunnels will have different influences on the tunnel structure and the surrounding strata.This thesis is based on the running tunnel from Sungang to Honghu of Shenzhen metro Line 7 and theoretical analysis,numerical simulation,indoor model test and other methods are used to study the effects of relative position changes of shield tunneling in overlapping tunnels.Firstly,indoor model test is used to analyze the influence on displacement and internal force of existing tunnel during construction of new tunnel while the two tunnels at different angle and same clear distance.Experimental results indicate that: In the case of constant clear distance and the overlapping tunnels are in a vertical position,the excavation of right tunnel has the greatest influence on the displacement and the additional bending moment and axial force variations of the left tunnel.As the angle decreases,the effect decreases and the effect on the vault is greater than the arch bottom,the maximum additional force variations is transferred from vault to hance.Secondly,the land subsidence,the displacement of segment,the changes in the stress state of segment and the development of plastic zone are analyzed by numerical simulation.Simulation results indicate that: In the case of constant clear distance,the vault will subside and bottom of segment will rise after the excavation of existing tunnel and with the increase of the angle,the displacement of both vault and bottom of existing tunnel are increasing while the absolute value of the left and right hance is decreasing;The bending moment of arch vault,arch bottom and left and right hance are all first increases and then decreases,and the axial force of vault and bottom decrease first and then increase while axial force of left and right hance is always decreasing;The excavation of the new tunnel causes the land subsidence continue to increase when the angle of two tunnels is small,but the land subsidence decrease when the angle of two tunnels is large;After the excavation of the new tunnel,the plastic zone of two tunnel are connected at all angles;The excavation of the new tunnel results in the displacement of the existing tunnel in negative x direction and positive z direction.After the angle is greater than 45 degrees,the maximum bending moment of the segment is shifted in a counterclockwise direction,and it become symmetry at 90 degrees.Meanwhile,when the angle is less than 30 degrees,the excavation of the new tunnel has the greatest impact of axial force on right hance of existing tunnel and after the angle is bigger than 45 degrees,the the greatest impact location transfer to left hance.Finally,the error between the model test and the numerical simulation is analyzed.The model test results of the relative displacement of the arch and the right hance are consistent with the numerical simulation results,and the relative displacement value of the numerical simulation is slightly larger than the model test results.There is a significant difference between the model test results and the numerical simulation results.The failed to simulate the stress release in model tests can lead to the error of internal force and the error will be greater with the increase of angle,which is verified by numerical simulation.