Influences of double-track shield tunnel construction on settlements of adjacent ground and buildings in a soft soil area

The influence of the shield tunnel construction on the adjacent grounds and buildings is a fundamental issue for the safe construction and regular service of the shield tunnel in the soft soil area. In order to investigate the influences of the double-track shield tunnel construction between the Tongde Road Station and the Shiqi Station of the Ningbo Metro Line 5 on the adjacent grounds and buildings, a dynamic 3D finite element model of shield tunneling is established. After comparing the simulated and monitered settlements of the ground surface and adjacent building, the influences of the tunnel construction on the adjacent ground surface and building are thereafter explored. The results show that when the excavation is completed, the subsidence tank deviates from the direction of the upward tunnel with an inverted trapezoidal shape, and the final cross-sectional influence area is less than 3 times the tunnel diameter from the center of the double-track tunnel axis. After the excavation of the ascending line, the surface settlement does not increase, but the width of the settlement groove increases. The settlement generated before the arrival of the downstream line accounts for 67% of the final cumulative settlement. The building inclines along the direction of shield tunneling as the shield reaches the building, while the building inclines along the opposite direction of shield tunneling as the shield leaves the building. The settlements at both sides of the building are reduced by 83%, compared with those at the middle part. After the two lines are connected, the settlements of the building shows a "U" shape distribution, and the maximum settlement occurring at the middle building is 0.5 m from the tunnel.