In situ testing and numerical investigation of vibration isolation using a single-row pile barrier subjected to train-induced vibration

Environmental vibrations induced by metro trains can affect nearby residents, historic buildings, and precision instruments. Installing vibration isolation barriers along propagation paths is a practical mitigation measure for existing metro lines. However, most existing studies used static or fixed-frequency harmonic loading, leaving the performance under moving train loads in layered ground insufficiently understood. This study combines full-scale in situ testing with 3D numerical simulations to investigate the vibration isolation performance of a single-row pile barrier under moving train loads along an at-grade metro line. A coupled layered ground-pile barrier model was established and validated using field measurements, and the effects of pile length, ground condition, and train speed were examined. The barrier significantly reduces vibration within 20–80 Hz, reaching approximately 20 dB at 25 Hz at a point 1 m from the pile axis. In layered ground, its performance is governed by whether the pile toe penetrates the soft-soil waveguide layer. When the pile toe extends into the underlying stiff layer, the piles and the stiff layer form a composite wave-impeding barrier, markedly improving far-field mitigation within 50–80 Hz. Increasing the train speed from 30 to 120 km/h amplifies the ground vibration response but has little effect on the barrier isolation performance. These findings clarify the isolation mechanism in layered ground and guide the design of single-row pile barriers near vibration-sensitive metro areas.