Rail vibrations caused by ground stiffness transitions

Kapitel i bok, 2009

Spatial changes in the material properties of the track and subground may lead to variations in the contact forces and the wheel-rail interface. A shift from one material to another can potentially induce transition radiation modes. The phenomenon has been observed in situations where the train goes onto a bridge. An advanced numerical model of the entire train-track-subgrade dynamic system with moving finite elements has been used to study the influence of material stiffness transitions in the subground. While the properties of the ballast and the rail where kept constant, the Young moduli of the two layers of clay representing the soil underwent a linear change over a short distance. Both transitions from soft to stiff and from stiff to soft soil were considered. The results indicate that the main effect of the transition is a temporary variation followed by a transient low-frequent vibration. The magnitude is relatively small and does not threat the stability of the system. The shielding track structure with ballast, sleepoers and pads evens out the disturbance.