Deformation analysis and protection measures of existing metro tunnels effected by river channel excavation in soft soils

Abstract

The excavation of river channel in soft soils has an inevitable influence on adjacent metro tunnels. This paper investigates the effect of river channel excavation on the underlying metro tunnels and corresponding protective measures based on an engineering project in Fuzhou city, China. A three-dimensional finite element model is developed to calculate the vertical and horizontal displacements and diametrical distortion of tunnels under different excavation sequences and soil reinforcement measures. Real-time monitoring of the vertical and horizontal displacements and diametrical distortion of tunnels is carried out and analyzed in detail. The results show that the vertical displacements and diametrical distortion of tunnels are primarily caused by the excavation of the river directly above the tunnels, while the horizontal displacements are induced by the excavation of the river next to the tunnels. A combination of cement slurry with a portal form and concrete with a plate form is recommended to reinforce the bottom soil of rivers and protect the operational tunnels. The accuracy of the calculation model and the effectiveness of the protection measure are confirmed by using on-site measurements. The findings can provide useful reference for the safety assessment and protection measures of similar projects.