An assessment methodology for tunnelling beneath bridges considering soil–structure interaction

The construction of the Tideway Tunnel in London induced ground movements that affected arch bridges along the River Thames. This study investigates the response of the Grosvenor Bridge (steel) and the Putney Bridge (masonry) to displacements induced by tunnelling, with a focus on soil–structure interaction (SSI) and the relationship between foundation movements and greenfield predictions. Coupled finite element (FE) analyses and spring-based two-stage analysis methods (TSAM), supported by field monitoring, are compared using elastic frame bridge models. The equivalence between plane-strain and three-dimensional FE representations is assessed, and TSAM formulations with varying spring complexities (derived from half-space theory) are evaluated. Results show that the TSAM is a practical and reliable tool for assessing tunnel–soil–bridge interactions, including transient conditions during the TBM approach. Greenfield displacements (or scaled variants) can be adequate for relatively flexible bridges. In contrast, for stiffer bridges, SSI alters the magnitude and shape of the foundation movements and the associated deformation mechanisms. Since response depends on relative bridge–foundation–soil stiffness, interaction analysis is recommended from the early design stages; a TSAM-based workflow is proposed to support early-stage assessments.