Deformation and Dynamic Response Analysis of Metro Shield Tunnel Under-Crossing Existing Railway Frame Bridge

［Objective］ At present, there are few studies on the interaction between the under-crossing shield and the upper vehicle-track structure. In order to ensure the safety of new metro shield construction and existing line operation, it is necessary to analyze the influence law of metro shield construction disturbance and train load on the deformation characteristics and dynamic response of the existing structure. ［Method］ Based on the Changsha Metro Line 6 shield tunnel project under-crossing the existing Beijing-Guangzhou Railway frame bridge , an excavation submodel of the shield tunnel under-crossing railway frame bridge and a vehicle-track dynamic coupling submodel are established. Numerical software is adopted for joint simulation to study the deformation of strata, frame bridge and track structure under different working conditions such as shield excavation process, grouting pressure, soil chamber pressure, stratum reinforcement, train speed, etc., so as to summarize the changing laws of vehicle-track dynamic response. ［Result & Conclusion］ The maximum settlement caused by advancing excavation of the shield left line is about 3.0 mm. After the excavation of the right line, the maximum settlement occurs at the position offset towards the center of the left and right lines, and the maximum settlement value reaches 5.4 mm. The track settlement caused by the advancing shield tunnel is slightly greater than the settlement caused by the following excavation; the car body vibration acceleration and the wheel-rail force increase when the train speeds up, and the wheel-rail vertical force is more affected by the train speed than by the wheel-rail lateral force; the vibration displacement, the car body vibration acceleration, the wheel-rail force and the derailment coefficient all gradually increase with the continuous advancement of the shield excavation, but not by much; after increasing grouting pressure, soil chamber pressure and taking ground reinforcement measures, the vertical rail vibration displacement is reduced by 14.7%, 11.5% and 44.1% respectively compared with the excavation without taking measures. During the shield construction process, ground reinforcement measures should be taken for the smooth shield tunnel construction and normal railway operation.