Numerical study on a deep excavation of transportation hub underlying operating railways and a metro station

The excavation of the transportation hub is located below Shanghai-Nanjing high-speed railways and metro station of Line 11. The surroundings are extremely complicated and the deformation controls of both the railway subgrade and the metro station are strict. 3D numerical simulation, using the FLAC^3D, is carried out to model the construction process of the deep excavation. The deformation behaviors of the retaining structures and the surrounding existing structures are investigated during the construction of the adjacent pit, underlying pit and the pits sharing the same diaphragm walls with the existing structures. Numerical predictions are verified by the monitoring data. The results show that both the settlement of the railway subgrade and the rebound of the metro station are controlled within the allowable values, and the numerical predictions are reasonable and close to the monitoring data. Deformations of diaphragm wall and settlement of railway subgrade can be reduced by deepening and thickening the diaphragm wall and improving the soils. The soils excavated at both sides of the existing metro station will result in rebound of the structures, and the rebound depends on the unloaded volume. The overlying railway subgrade heaves as a result of the interaction of the underlying excavation and the train loads.