Abstract: The characteristics and propagation mechanisms of train-induced vibrations in high-speed railway shield tunnels are critical for route selection and the assessment of vibration-induced environmental impacts in densely built urban areas. In this study, a train-induced vibration prediction model is established based on a 2.5-dimensional finite element method-method of fundamental solutions (2.5D FEM-MFS). Focusing on a 350 km/h high-speed railway shield tunnel with an external diameter of 13.8 m, wheel-rail coupling dynamics and wavenumber-domain field coupling analyses reveal the vibration source characteristics and propagation patterns under typical operational conditions. The primary findings are as follows: (1) Train-induced vibrations in high-speed railway shield tunnels exhibit distinct frequency-dependent propagation; components below 30 Hz primarily propagate as shear waves in the surrounding rock (734 m/s wave velocity), components within 30-70 Hz involve coupled vibration of the tunnel and soil, and components above 80 Hz are dominated by segment bending waves (1 066 m/s and 2 000 m/s). (2) The Z vibration level attenuates from 80.9 dB at the track slab to 47.6 dB at the crown, with localized amplification up to 55 dB at the sidewalls due to higher-order vibration modes. (3) Surface vibrations exhibit non-monotonic spatial attenuation with localized amplification, where the maximum Z vibration level of 46.1 dB occurs 43 m from the tunnel centerline (complying with Class Ⅰ vibration limits), and the maximum velocity of 1.73 μm/s meets VC-E criteria for precision instruments. (4) Compared to typical metro vibration conditions, high-speed railway shield tunnels exhibit lower internal Z vibration levels and reduced surface high-frequency band vibration levels, although the latter attenuates more gradually with distance.

Key words: high-speed railway underground lines, shield tunnels, environmental vibration, 2.5-dimensional finite element method-method of fundamental solutions