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• Dynamic response and crack propagation law of a lossy invert were investigated. • Dynamic stress/strain exhibit rapid attenuation in shallow region of tunnel invert. • Invert and invert filling are the primary carriers of dynamic load. • Initial cracks exhibit swivel propagation under dynamic load of train. This study investigates the vibration characteristics of a lossy tunnel invert and the propagation law of initial cracks under the dynamic load of a train, based on field tests conducted in the Fuchuan Tunnel of the Lanzhou–Urumqi High-Speed Railway. Dynamic resistance strain gauges were embedded in the invert structure and the propagation law of initial cracks under dynamic loads was studied using low cycle fatigue analysis. The results demonstrate that the attenuation of dynamic strain and dynamic stress in the shallow region of the tunnel invert was rapid and gradually slowed with an increase in depth. Furthermore, most of the dynamic stress was borne by the invert structure. Thus, the invert and its filling are the primary carriers of the dynamic load of the train. The initial crack below the track exhibits swivel propagation under the dynamic load of the train and extends until it penetrates the surface of the invert forming interconnected cracks. Consequently, the concrete in the crack loses its bearing capacity. Under the static load of the surrounding rock, the initial crack extends downwards, toward the centre of the invert. The initial crack at the centre of the invert also exhibits swivel propagation under the dynamic load of the train. Under the static load of the surrounding rock, the initial crack extends vertically downwards until it penetrates the central ditch. These results are extremely significant for the optimisation of tunnel invert design, to ensure the safety of train operations. [ABSTRACT FROM AUTHOR]