Influence of Water Ingress at the Shield Tunnel Portal on Tunnel Deformation and Load Capacity Weakening

Abstract. During the construction of shield tunnels, adverse geological conditions can lead to tunnel segment settlement and damage. This study investigates the deformation patterns and changes in load capacity of shield tunnels under water ingress conditions at the portal, using a segment of the Jinan Metro as a case study. Through field measurements and numerical simulations, we analyzed the structural deformation and weakening of load capacity caused by water ingress. The results indicate that significant settlement occurs at both the tunnel crown and invert after water ingress, with a maximum settlement of 181.2 mm compared to the original design axis. The deformation profile of the tunnel primarily resembles a transverse "duck egg" shape, while the segments near the portal exhibit vertical "duck egg" deformations due to grouting and other factors. Multiple cracks and damages were observed in the segments, with up to 16 cracks found in a single ring. Compared to the original design conditions, the bending moment in the tunnel lining increased by approximately 7%, and the axial force increased by about 9%, leading to an 11% reduction in tunnel resistance effects. The findings of this study regarding tunnel lining deformation and load capacity weakening provide valuable insights for similar engineering projects.