An analysis of the settlement of a shield tunnel passing under the operating railway bridge

Research on the shield tunnel of the Xiang-Sha bid section of Dalian metro is done to analyze the effect of the surface settlement by 3D finite element simulation, combined with in situ monitoring data. The results show that the surface settlement undergoes five stages: initial disturbance settlement, settlement in front of excavation, settlement above shield machine, settlement of shield passing and consolidation settlement. The overall shape of the surface settlement is a groove, the surface settlement of the central line of the tunnel is large, and the settlement of both sides of the tunnel is small. The settlement is symmetrical with the axis of the cross section of the tunnel, which conforms to the mechanism of the surface settlement and is consistent with the field monitoring data. The closer the tunnel is to be excavated, the larger the overall settlement displacement is. When the shield excavation is less than 20 m, the settlement displacement expands both horizontally and longitudinally. When the tunnel is excavated to 40 m, the settlement displacement mainly expands along the longitudinal direction, but the lateral expansion is not obvious. The funnel-shaped subsidence is the largest on top of the tunnel, and it decreases on two sides. The settlement curve is basically symmetrical, but the settlement on the right side is slightly larger than the left side because of the excavation of the right line tunnel. The whole pile is on the fracture surface of the tunnel, it belongs to the category of short piles and the deformation of the bridge pile is mainly caused by the vertical settlement of soil.