Page 319 - 360.revista de Alta Velocidad - Nº 5

Development of an alternative maintenance technique for railway ballasted tracks

2016a). For each maintenance solution, this test began over the conventional section (rail,
sleeper, fastenings, rail pad and ballast, without USPs and without blown stones), and it was
stopped when the settlement was close to 15 mm and the loading cycles reached approximately
50,000. Following this procedure, a maintenance task was carried out to recover the track
geometry, whereupon the test continued until its completion (200,000 cycles). This method was
applied twice for all the techniques studied.

The conventional stoneblowing process was conducted after the ballast settlement (up to
approximately 15 mm, as indicated previously) by lifting the rail-fastener-sleeper system,
and adding the small stones between the sleeper and the ballast surface, which allowed
for recovering the original position of the sleeper. In this laboratory work, the process of
adding the stones was developed by hand (without compressed air) since the main objective
of this initial study was to show the effect of the elastic components, and in particular to
examine the feasibility of using rubber particles as flexible stones. The volume of stones and
distribution under the sleeper was in agreement with the findings of other authors (Nutbrown
and Nicholas, 1999; Tutumluer et al., 2015). Finally, the sleeper piece was returned to its
original position (corresponding to its location before ballast settlement), and the dynamic
test was continued.

Regarding the combination of stoneblowing with the different elastic elements, in the
case of USPs, these components were glued to the bottom of the sleeper by using epoxy
resin while the process of stoneblowing was carried out, and then the sleeper with the
pad was again placed over the ballast and the stones blown. In reference to the rubber
particles (RP) used for stone-rubber blowing process, they were mixed with the natural
stones so that both materials were applied at the same time. The quantities of rubber
analyzed were 10%, 25% and 50% over the total volume of the mix of elastic particles and
natural stones.

3. Analysis of results

Figure 3 analyses the influence of adding different quantities of rubber particles (as
replacement of natural small aggregates used during stoneblowing intervention) on the
variation in mechanical performance of the global section in comparison to the effect
of only apply stoneblowing process (without including innovative elastic solutions).
Also, as a referent elastic element to analyse the effect of rubber particles, Figure 3
shows the impact of including USPs in combination with stoneblowing process.

It is possible to understand that the inclusion of USPs and rubber particles during
stoneblowing operation, leads to an important reduction in track stiffness while
increasing the damping capacity of the section, limiting the negative effect of stiffening
of the track when conventional stoneblowing is applied. Also, results show that the
use of different percentages of rubber particles allows for gradually varying the track
performance, obtaining comparable results to those measured for USPs. Indeed, the
replacement of more than 50% of stones with rubber particles presents a comparable
reduction in section stiffness to that obtained with soft USPs while a percentage around
10% could be appropriate to use this solution as alternative to stiff USPs. Then, it is seen
that the mix of different ratios of rubber particles and stones for track maintenance
would allow for the optimization of its vertical stiffness, which is particularly beneficial
in transition sections where a gradual change in stiffness is required.

International Congress on High-speed Rail: Technologies and Long Term Impacts - Ciudad Real (Spain) - 25th anniversary Madrid-Sevilla corridor 317