Measurement of Dynamic Response and Analysis of Characteristics of Heavy-Haul Railway Tunnel Bottom Structure Under Train Loading

This study investigates the dynamic response characteristics of the tunnel bottom structure, focusing on a heavy-haul railway tunnel. To assess the condition of the tunnel bottom, geological radar and drilling core techniques were employed, along with on-site dynamic testing. The dynamic stress and acceleration response characteristics of the tunnel bottom structure, situated in grade V surrounding rock, were analyzed under axle loads of 25 t, 27 t, and 30 t. Both time-domain and frequency-domain analyses were conducted to explore the impact of structural defects on the dynamic response of the tunnel bottom. The results indicate that the dynamic response of the tunnel bottom structure increases linearly with increasing train axle load. In the presence of void-related defects at the tunnel bottom, the dynamic response of the structure is amplified, with an observed growth rate of up to 26.3%. Furthermore, the load exerted by heavy-duty trains on the tunnel bottom structure is predominantly a low-frequency effect, concentrated within the range of 0–20 Hz. Analysis of the 1/3 octave band reveals that the maximum difference in acceleration levels occurs at a center frequency of 31.5 Hz. Additionally, as the distance between the measurement point and the vibration source increases, the dynamic response induced by the void defect on the tunnel bottom structure weakens.