Deformation influence of large cross-section quasi‑rectangular shield tunnel parallel crossing existing shield tunnel

To investigate the influence of a large cross-section quasi-rectangular shield tunnel passing in parallel with existing shield tunnels, a three-dimensional numerical simulation was conducted using Plaxis 3D software, based on the typical geological conditions in Zhengzhou. The construction of a new single-tube double-track large cross-section quasi-rectangular shield tunnel passing in parallel with the existing Zhengzhou Metro Line 5 tunnels was simulated. The results indicate that the ground deformation induced by the quasi-rectangular shield tunneling exhibits a funnel-shaped settlement pattern above the tunnel and a U-shaped heave pattern below the tunnel. The maximum deformation of the existing tunnel occurs in the horizontal direction (X-direction), manifesting as an overall outward displacement of 8.636 mm, and the maximum total deformation of the existing tunnel is 8.660 mm. The recommended values for the chamber pressure, and tail void grouting pressure are 0.15 MPa, and 0.24–0.26 MPa, respectively. Shield shell friction should be minimized. In the simulation, 15 kN/m² is the lower bound. In practice, it can be reduced by foam, bentonite slurry, polymer conditioning, and anti-friction coatings.