Study of the characteristics of train-induced dynamic SIFs of tunnel lining cracks based on the modal superposition approach

Cracks on a tunnel lining are commonly observed during in-site tunnel inspection. The cracks are generated owing to various reasons and can potentially further propagate as they are subjected to repeated dynamic train loads during the entire tunnel service life. The study investigated train-induced dynamic stress intensity factors (SIFs) of tunnel lining cracks by numerical simulations using the modal superposition approach and examined the effects of a wide range of factors. The methodology of the modal superposition approach was adopted and validated to determine dynamic SIFs. Subsequently, the coupled dynamic FE model was established to calculate train-induced SIFs of tunnel lining cracks and radiation damping owing to the infinite surrounding medium was determined. Finally, a parametric analysis was conducted to investigate the effects of crack location, crack depth, wave velocity of the surrounding medium, and material damping on dynamic SIFs of tunnel lining cracks subjected to metro train loads. The results demonstrate that the modal superposition approach can be employed to accurately and effectively calculate the train-induced dynamic SIFs of tunnel lining cracks when radiation damping is considered. The effects of crack location, crack depth, and wave velocity of the surrounding medium are significant, while the effect of material damping is not considerably evident. The maximum dynamic SIF significantly increases with crack depth, while it decreases with the wave velocity of the surrounding medium and material damping ratio. Cracks with greater depth in the poorer medium are more likely to propagate under dynamic train loads.