Page 321 - 360.revista de Alta Velocidad - Nº 5

Development of an alternative maintenance technique for railway ballasted tracks

On the other hand, Figure 5 compares the effect of rubber particles and USPs on reducing the
stress on ballast layer, in reference to the conventional stoneblowing process. Considering that
the application of such conventional technique already allows for reducing pressure in the
ballast (as a result of the increase of the surfacing contact between sleeper and ballast when
smaller stones are added) (Coenraad, 2001; Sol-Sánchez et al., 2016b), results show that the
solution with 10% of rubber presented lower reduction than the conventional stoneblowing task,
obtaining then a negative decrease in comparison to such reference technique. This is likely to
be related to the flexibility of these few particles (having a high capacity to deform under low
stress) that cause the concentration of pressure on the natural stones in contact with sleeper.
However, when the quantity of rubber was increased (and there are also rubber particles
between the sleeper and the small natural stones), the pressure on the ballast layer was
reduced, showing even higher reduction in pressure than that measured for the solutions with
USPs. This is due to the strong capacity of the rubber particles to damp loads, associated with
their size (up to 20 mm), which is higher than the thickness of the USPs studied.

Figure 5. Impact of the elastic solutions on the reduction in ballast pressure, in reference to conventional stoneblowing.

With the aim of analysing ballast degradation after each type of maintenance task based
on elastic solutions, Figure 6 displays the effect of combining stoneblowing with USPs
and the inclusion of rubber particles as flexible aggregates on two parameters (Index of
particle breakage - Bg; Ballast Breakage Index - BBI, %) that have been previously used in
other studies to evaluate ballast breakage (Marsal, 1967; Indraratna et al., 2005). As the
values recorded for the solutions with the same type of elastic element (USP or RP) were
quite similar, Figure 6 shows the mean value recorded for the reduction in degradation
when stoneblowing process is combined to both USPs (stiff and soft) and to the different
quantities of rubber particles.
The results reflect the fact that both elastic solutions allow for a significant reduction in
ballast breakage (regardless of the parameter selected), this fact being more marked when
rubber particles were used during the stoneblowing task. This could be related to the better
distribution of the stress and lower movement of the ballast stones, which is in accord with the
results of ballast settlement and pressure under the granular layer. Thus, it is clear that the use
of stone-rubber blowing could lead to an important increase in the durability of ballast, and
therefore, in the service life of ballasted tracks.

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