Effect of Excavation Sequence on Surface Settlement and Segment Deformation of Treble-Hole Shield Tunnel

In order to investigate the influence of excavation sequence of three-line parallel shield tunnel on ground surface settlement and segment deformation, teking the tunnel construction of Nantong Metro Line 1 as the engineering background, FLAC3D software is used to simulate the tunneling process of three-line parallel shield tunnel under three cases of "right-center-left", "center-right-left" and "left-right-center", and the deformation pattern of the ground surface and shield segment is analysed. For the ground surface deformation, it is found that the width of the settlement trough is basically the same, but there are differences in the maximum surface settlement values. The order of surface subsidence caused by the three cases is as follows: Case 2 > Case 1≈ Case 3. For the segment deformation, the tunnel deformation is changed from a standard circle to an ellipse with flat top and bottom and wide ends, but there are differences in the offset process and the final segment convergence value. The segment deformation of the antecedent tunnel caused by the three case is arranged in descending order: Case 3 > Case 2 ≈ Case 1. Numerical simulation results show that when the "right-center-left" construction sequence is used, the maximum ground surface settlement and segment deformation is smaller, which can effectively guarantee the safety of tunnel construction. It is recommended to choose this excavation sequence in the actual construction process. The maximum settlement value obtained from the simulation was - 11.8 mm, and the maximum settlement value predicted by the Peck formula was - 11.1 mm, with errors of 1.46% and 4.78%, respectively, compared with the maximum settlement value of -11.63 mm obtained by fitting the measured fitting data.