Page 322 - 360.revista de Alta Velocidad - Nº 5

Sol-Sánchez, Miguel. Moreno-Navarro, Fernando. Rubio-Gámez, Mª Carmen.

Figure 6. Effectiveness of the elastic solutions to reduce ballast degradation, considering stoneblowing process as a reference.
4. Conclusions

This paper presents a study about the effect of adding rubber particles as flexible stones during
the process of stoneblowing, regarded as a new maintenance task (stone-rubber blowing) for
railway tracks that combine the benefits of both stoneblowing and USPs (but without the need
of bonding such elastic elements) by obtaining an elastic granular layer that fill the gap between
the sleepers and the settled ballast layer. With this purpose, this paper shows the influence
of adding different quantities of rubber particles as flexible stones at the time that its effect
is compared with that recorded when conventional USPs (with different stiffness) are used in
combination with the traditional maintenance tasks (tamping and stoneblowing). Based on the
results obtained in this study, the following conclusions can be drawn:

- The inclusion of rubber particles during the stoneblowing process improves the effectiveness
of this task to reduce ballast settlement and degradation, at the same time that the flexibility
and capacity of the granular layer to damp loads is increased, and therefore, longer service
life of railway tracks could be obtain.

- The higher the quantity of rubber particles used as flexible stones, the higher the reduction
of ballast settlement (at both short and long-term) and vertical stiffness while higher
capacity to dissipate the energy transmitted to the ballast is recorded as well as lower
stress under such granular layer.
- The use of high quantities of rubber particles (around 50% over the total volume of particles
blown) during the process presented as stone-rubber blowing, leads to a comparable (or
even better) behaviour of the ballast than that recorded when soft USPs are employed in
combination with the conventional stoneblowing process (the most favorable case among
the conventional maintenance tasks).

- On the other hand, lower volume of rubber could be comparable to the cases of conventional
stoneblowing where stiffer USPs are applied, being able to obtain a gradual behaviour of
railway tracks by varying the quantity of rubber employed during the process of blowing.
This would allow for smooth stiffness transitions along the track.

Based on the results, it is possible to say that the proposed technique of adding rubber particles
to partially replace the stones leads to similar or enhanced benefits in comparison with those
obtained when other elastic components such as USPs are applied. Moreover, use of this
technique could yield a substantial reduction in maintenance costs, since these rubber particles
could be combined with the small stones during the stoneblowing process. Nonetheless, further

320 360.revista de alta velocidad