Field Measurement and Numerical Simulation of Train-Induced Vibration from a Metro Tunnel in Soft Deposits

Abstract

Train-induced vibration is increasingly attracting people’s concern nowadays. In the coastal areas, many metro tunnels are built in the soft deposits, so the train-induced vibration effect is more serious. Nevertheless, the existing research studies mainly focus on the dynamic responses in the tunnel or on the ground surface while vibration characteristics in the ground are seldom studied. In this paper, a comprehensive field measurement was performed by installing accelerometers in the tunnel and soil layers and on the ground surface to capture the response characteristics of the track-tunnel-ground system. Elastoplastic numerical simulation considering the soil-water coupling was conducted to reveal the responses of acceleration, dynamic displacement, and excess pore water pressure using FE code DBLEAVES. Measurement results indicate that high-frequency contents (>500 Hz) attenuate rapidly in the propagation process; the dominant frequency of the rail concentrates in the middle- and high-frequency bands, about 25–400 Hz and 1000–1500 Hz, while the frequencies of the track bed, soil layers, and ground surface drop to below 400, 200, and 100 Hz, respectively. The vertical ground acceleration decreases like an arc in the transverse direction while there is transverse acceleration amplification phenomenon at a distance from the upper haunch and lower haunch of the tunnel. Overall, the area affected by train vibration in the soft deposits is about 30 m away from the metro tunnel. Numerical simulation based on soil-water coupled analysis is feasible to model the vibration characteristics in the soft deposits and confirms that there is acceleration amplification in the ground. Moreover, numerical results indicate that excess pore water pressure can be accumulated during each train vibration, so the train-induced settlement will be a potential problem in the long term for the metro tunnel.