Ground and tunnel deformation induced by excavation in pipe-roof pre-construction tunnel: A case study

Abstract

The tunnel crossing project of Taiyuan Railway Station was constructed through the pipe-roof preconstruction method to minimise the disturbance of the construction to the railway station. Twenty 2 m-diameter steel pipe jacks each were used each ring in this method. The spacing between adjacent jacking pipes was 165–265 mm. To ensure the stability of the pipe-roof preconstruction tunnel and the normal operation of the train during the earthwork excavation process, the soil pressure on the outside of the tunnel, tunnel deformation, track settlement and strain, and reinforcement stresses in the concrete of the tunnel envelope were monitored. The monitoring results show that vertical deformation of −2.7 mm occurred in the tunnel roof during the excavation process. A horizontal deformation of ±0.6 mm on the left and right sides of the tunnel and vertical deformation of +1.38 mm on the tunnel floor were also observed. The strain in the concrete due to the excavation and the change in stress in the reinforcement were within the elastic range of the material, indicating that the deformation of the tunnel was safe. The tunnel deformations calculated by simplifying the tunnel roof and floor to the arch model were in good agreement with the measured results. The surface track settlement monitoring results indicate that a settlement difference of 1–4 mm was rapidly generated at the surface during the train passage after the earthwork. However, the settlement returned to the previous level after the train passed the monitoring point. The maximum surface settlement after soil reconsolidation and stabilisation was less than 0.5 mm. These results suggest that the earth excavation of the tunnel have little impact on the safe passage of trains. The findings of the research could provide importance reference for the tunnelling project with similar problems.