Analysis of the Effect of Shield Tunnel Construction Method Under Viaduct on Tunnel Structure and Pile Foundations

To ensure the safe operation of elevated bridges during shield tunneling, this study investigates the west extension of Shijiazhuang Metro Line 1, where the tunnel passes beneath an existing elevated bridge. Field monitoring data serve as validation. A numerical model was developed using FLAC3D based on site-specific geological conditions to examine three schemes: (1) a 0.7 m clearance between the tunnel and pile foundation; (2) earth pressure balance shield (EPBS) cuts through the bridge foundation piles; and (3) pre-reinforcement of the surrounding soil using a U-shaped Metro Jet System around the cut pile. In Scheme 1, the pile exhibits longitudinal deformation aligned with the tunnel’s advance direction. Vertical deformation presents an S-shaped profile, and lateral displacement remains negligible. The most pronounced pile deformation occurs from 2.4 m behind to 0 m ahead of the pile. In Scheme 2, lateral deformation remains constrained, but vertical and longitudinal deformations increase markedly. Maximum surface settlement occurs directly above the pile, and the tunnel lining becomes elliptical. In Scheme 3, relative to Scheme 2, longitudinal and lateral pile deformations exhibit little change, while vertical pile deformation, surface settlement, and tunnel lining distortion are significantly reduced.