Mechanism and Law Analysis on Ground Settlement Caused by Shield Excavation of Small-Radius Curved Tunnel

The mechanism of ground settlement caused by the construction of small-radius curved tunnels is more complicated compared to straight tunnels. This paper takes Changzhou Metro Line 2 as an example, comprehensively considers the additional thrust of the tunnel face, the grouting pressure of the shield tail, the friction between the shield shell and surrounding soil, and the ground loss. The analytical methods, numerical simulation and field measurement are used to compare and study the law of ground settlement of small-radius curved tunnels. The results show that the main factors that induce surface deformation during shield construction of small-radius curved tunnels are ground loss and shield shell friction. The ground settlement caused by the ground loss accounts for about 90% of the total settlement, while the shield shell friction mainly causes ground heave. The deformation of the transverse plane of the tunnel is distributed asymmetrically along the tunnel axis, showing a curved shape with a small radius, and the ground settlement in front of the tunnel shows a "W" shape. Meanwhile, the ground settlement is negatively correlated with the increase in the radius of curvature. As the radius of the curve decreases, the surrounding soil of the curved tunnel shows a tendency to tilt toward the tunnel. This research can provide basis and data support for the ground settlement prediction of shield construction of small-radius curved tunnel.