Abstract: In Ningbo soft soil area, the problem of excessive deformation of shield section of the tunnel can be effectively solved by means of gate reinforcement, “tofu” block excavation and in-channel pressure. The Midas GTS NX finite element method was used to study the effect of river block excavation on the deformation of the shield section of Rail Transit Line No. 1 directly in the Ningbo soft soil area. Compared with the measured results, it is shown that with different construction conditions of the river excavation, the horizontal displacement of shielded tunneling interval increases gradually. The maximum horizontal and vertical displacements of the tunnel are in good agreement with the field measurement results during the excavation of the river channel. The deformation of shielded tunnel is in a low deformation level. The effect of soil reinforcement process should be considered for shield deformation. When the triaxial cement mixing pile is constructed, the cement is mixed into the soil body, which leads to the increase of the soil weight and the increase of the dead weight of the soil body, which leads to the sinking of the shield tunnel in the lower section. With the excavation of river channel, the uplift deformation of shield section increases gradually. The main characteristic is that the excavation of the river in the secondary affected area on both sides has a great influence on the uplift deformation of the interval shield tunnel, followed by the influence caused by the main affected area directly above the shield tunnel. When the river is open to water, the small settlement of the interval shield tunnel appears.

Key words: Soft Soil, River Excavation, Zoned Construction, Shield Tunnel, Numerical Simulation