Shield tunnelling effects on adjacent railway bridge piles and reinforcement measures

Shield tunnelling adjacent to existing railway bridge pile foundations may disturb the surrounding soil and induce additional pile deformation, settlement, uplift and internal force redistribution. To investigate the influence of shield tunnelling on adjacent bridge pile foundations and to evaluate effective deformation-control measures, this study takes the Shanghai Metro Chongming Line Phase I project as a case study, where a shield tunnel passes beneath the Shanghai–Nantong Railway Phase II bridge. A three-dimensional finite element model was established to simulate the full tunnelling process, and theoretical calculation and field monitoring were used to verify the reliability of the numerical results. The two-stage method was also adopted to analyse the effects of shield thrust, shield-shell friction, grouting pressure and ground loss on pile displacement. The results show that, without reinforcement, the maximum uplift at the bridge-pier top reached 6.23 mm, exceeding the allowable displacement control limit of ± 4 mm. The maximum horizontal pile displacement and bending moment were mainly concentrated near the tunnel centreline elevation, indicating that this zone is the key control region for pile deformation and internal force response. Both isolation piles and Metro Jet System (MJS) reinforcement reduced pile deformation, while combined reinforcement schemes showed better deformation-control performance. Among the compared schemes, the fully enclosed isolation-pile system with capping beams reduced the maximum horizontal pile displacement by approximately 92% and was adopted for construction control. Field monitoring further confirmed the reliability of the numerical simulation. The findings provide a reference for deformation control, reinforcement selection and construction risk management in shield tunnelling projects adjacent to existing bridge pile foundations.