Some results from the application of the model are presented, as the dynamic responses of several types of high speed tracks (softening the existing railpads), sleepers and ballast (under sleeper pads) mainly in terms of accelerations at different levels of the track.

In particular, the techniques for improving the track substructure, such as placing the bituminous subballast as an alternative to granular subballast, was investigated.

In order to accomplish this research, four different track solutions from which three incorporate bituminous mixture subballast, were tested in a laboratory facility. At the same time these track configurations were modelled, so as to calculate the mechanical and physical behaviour and also to estimate dynamic responses as a function of increasing train speeds. Numerical results enabled some interesting conclusions to be drawn concerning the correct cross-section composition, namely the thickness of the subballast layer and the characteristics of the supporting layers that would provide a better mechanical and dynamic behaviour of the track.

This paper also shows track settlement evolution by numerical simulations of decades of track service with the passing tonnage. Throughout these computations, the initial defects imposed increase gradually and the position of the rail and track geometric levelling is progressively altered and updated. In each cycle of settlement updating, time simulation is performed considering (short-term) responses in all sleepers of the track arising from the new position and updated irregularities.

Hence, different track design solutions already confirmed to improve dynamic behaviour at very high speeds were also analysed in a long-term perspective and positive effects in delaying track deterioration progression have been demonstrated for the different track solutions analysed, such as: softening railpads, introducing under sleeper pads (USP) or using bituminous subballast.

From the numerical results presented, certain enhancing design solutions could be recommended in order to reduce track vibrations and the number and frequency of maintenance interventions. Therefore, apart other advantages already demonstrated in other previous studies, the use of bituminous subballast seems to also be favourable to improve track dynamic behaviour and to extend its lifetime with the consequent savings in maintenance costs.

Predictions of track deterioration can be an important supporting tool for life-cycle cost analyses of a particular railway infrastructure. Indeed, these predictions can help suggestingthe suggestion of track design solutions to improve track overall performance at very high speeds, as it is expressed in this paper.

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