*2.1. Project Introduction*

The left line from Hongguzhong Avenue Station to Yangming Park Station of Nanchang Metro Line 2 is 2335 m long, and the minimum plane curve radius is 600 m. In this section, the mud–water balance shield construction technique was adopted, and several bridge piles of the south approach bridge of Bayi Bridge invaded the tunnel section, as shown in Figure 1. For the invaded the subway tunnel line, there are seven pile foundations in ramp C and ramp F, of which ramp C has a deck width of 11 m, and the upper structure of the bridge is a two-box multi-span reinforced concrete continuous box girder bridge. The ramp F has a deck width of 7 m, and the superstructure of the bridge is a single-box multi-span reinforced concrete continuous box girder bridge. The pile foundations intruded into the tunnel are all single-column and single piles, so these invaded pile foundations need to be underpinned. The Bayi Bridge spans the Ganjiang River, and is an important transportation hub in Nanchang, hence there are strict requirements on structural deformation and stability. However, in this project, performing the single-column and single-pile underpinning is extremely risky in the narrow space of the curved and unclosed bridge section, and it is extremely difficult to control the stability of the underpinning pile foundation and bridge structure during the construction process.
