railway track stiffness variations – consequences and countermeasures

the track stiffness experienced by a train will vary along the track. sometimes the stiffness variation may be very large within a short distance. one example is when an unsupported sleeper is hanging in the rail. track stiffness is then, locally at that sleeper, very low. at insulated joints the bending stiffness of the rail has a discontinuity implying a discontinuity also of the track stiffness. a third example of an abrupt change of track stiffness is the transition from an embankment to a bridge. at switches both mass and stiffness change rapidly. the variations of track stiffness will induce variations in the wheel/rail contact force. this will intensify track degradation such as increased wear, fatigue, track settlement due to permanent deformation of the ballast and the substructure, and so on. as soon as the track geometry starts to deteriorate, the variations of the wheel/rail interaction forces will increase, and the track deterioration rate increases. in the work reported here the possibility to smooth out track stiffness variations is discussed. it is demonstrated that by modifying the stiffness variations along the track, for example by use of grouting or under-sleeper pads, the variations of the wheel/rail contact force may be considerably reduced.