Investigation on Effect of Unilateral Train Load on Lining Structure and Inverted Arch Trestle Bridge in Double-Arch Tunnel Under Construction

Previous studies of train-induced tunnel responses have mainly focused on completed tunnels or symmetric loading conditions, while the dynamic behavior of unfinished double-arch tunnels subjected to unilateral train loading through temporary trestles remains insufficiently understood. To address this gap, this study investigates the asymmetric load-transfer mechanism and short-term structural response of an unfinished double-arch tunnel–trestle system and identifies critical locations for construction-stage monitoring and speed control. A three-dimensional ABAQUS model was established for train speeds of 10–70 km/h and validated using a 63-day field-monitoring program comprising 15 train passages at speeds of approximately 9.4–56.2 km/h. Both numerical and monitoring results show that stress and deformation increase with train speed and are concentrated at the loaded-side invert, lower middle partition wall, and trestle wheel-load region. At 70 km/h, the calculated maximum lining compressive stress and trestle stress reached 6.353 and approximately 172 MPa, respectively, while the maximum horizontal deformations of the loaded and unloaded tunnel bores were 1.110 and 0.565 mm. At the maximum monitored speed of 56.2 km/h, the measured peak compressive stress of the middle partition wall was 5.95 MPa. The mean monitoring-to-simulation ratios for the evaluated responses were approximately 0.94–0.97, demonstrating satisfactory agreement and a slightly conservative numerical prediction. The results clarify the asymmetric coupling response of the tunnel–trestle system and support the identification of sensitive monitoring locations. Based on the combined numerical and field evidence, approximately 30 km/h is recommended as a conservative, project-specific construction-stage operational-control value. This study provides a quantitative basis for monitoring and risk control in similar temporary rail-transport projects, although further verification under different geological, structural, and loading conditions is required.