Impact of Shield Tunnel Under-crossing on Deformation and Internal Forces of Railway Rigid-Frame Bridge

Objective Railway rigid-frame bridges are sensitive to deformation due to the rigid connection between piers and girders. Moreover, owing to their small span and low pier height, it is difficult to install isolation piles when metro shield tunnels under-cross such bridges. Therefore, it is necessary to study the impact of metro shield tunnel direct under-crossing on the deformation and internal force of railway rigid-frame bridges.

Method Based on the project of Hefei Metro Line 4 under-crossing a railway rigid-frame bridge, the finite element method is adopted to compare and analyze the middle-span and the side-span under-crossing schemes. The reliability of the finite element analysis is verified by field monitoring data.

Result & Conclusion In the middle-span under-crossing scheme, the superposition effect of the double line shields results in a maximum pier settlement of 1.504 mm and a differential settlement of 0.606 mm between adjacent piers. In the side span under-crossing scheme, although the clearance between the shield and bridge piles increases, the shield under-crosses closer to the railway abutment, leading to a maximum abutment settlement of 2.533 mm and a differential settlement of 1.649 mm between adjacent piers (abutments). Structural calculations show that the additional internal forces induced in the middle-span under-crossing scheme are larger, but remain within the safety range. The side-span scheme aggravates abutment deformation and eccentric load, posing greater relative risks during construction and operation. In addition, the shield in the side-span under-crossing scheme is located on a curved section, which is less favorable for ground loss control compared to a straight section. Through comprehensive comparison, the middle-span under-crossing scheme proves better. After adopting this scheme, field monitoring data indicate that during shield under-crossing, the piers experience heave first and then settlement, and the pier settlement gradually stabilizes about one month after shield tail detachment. The maximum pier settlement is approximately 1.604 mm, and the maximum differential settlement between adjacent piers is 0.738 mm. The field monitoring data aligns well with the calculated results, demonstrating the reliability of the finite element method.