Dynamic response and long-term settlement of a metro tunnel in saturated clay due to moving train load

The purpose of this study is to investigate the train-induced settlement of a metro tunnel in saturated clay through the soil-water full coupling dynamic finite element method (FEM). The train vibration load is first evaluated using the rail-fastener-tunnel-subgrade model and then applied to the track bed to simulate the movement of metro train in the 3D model. Cyclic Mobility Model introduced in the numerical analysis to simulate the mechanical behavior of saturated soft clay. Three cases of numerical analyses are conducted to study the train-induced vibration in saturated clay, e.g., dynamic responses on the ground surface and excess pore water pressure (EPWP) around the tunnel. The calculations are conducted using the finite element program DBLEAVES. Particular attention is paid to the response difference between the soil-water coupling analysis and the single-phase analysis with a 3D model, and the difference between a 2D and 3D soil-water coupling analysis. It was found that the dynamic responses from the coupling analysis and single-phase analysis differed significantly. The presence of underground water may greatly weaken the ground vibration and decrease the accumulation rate of ground settlement. The ground surface acceleration, displacement and accumulated EPWP evaluated from a 2D analysis are far larger than those from a 3D analysis. Train vibration in trial operation was simulated by 2D and 3D models to verify the feasibility of the numerical method proposed in this paper in evaluating train-induced settlement. Finally, the long-term tunnel settlement in normal operation was predicted by the 2D model, and it was concluded that the final settlement of a metro tunnel in saturated clay due to repeated train vibration may reach 80 mm.