Page 327 - 360.revista de Alta Velocidad - Nº 5

Control and Maintenance of Railways through Satellites.
Is it possible?

In any element, we can distinguish two main types of maintenance, according to the occurrence
of the failure: preventive maintenance, when maintenance aims to avoid failure, and corrective
maintenance, which is done when the failure of the element has already occurred.
Preventive maintenance operations aim to minimize the likelihood of a failure in the elements,
due to the associated operating risks and the higher cost that the corrective maintenance
associated with the failure entails. Within preventive maintenance, we can distinguish the
predetermined maintenance (which is performed according to established time intervals or
operating units), and maintenance based on the condition, where the condition of the element
is monitored or inspected to determine the actions to be undertaken.
The railways are composed of a multitude of elements, with different modes of degradation and
maintenance operations. To determine how we can facilitate or improve maintenance through
the use of satellites, it is necessary to analyse the operations necessary to know the state of
the different subsystems. These surveillance operations can be done both on foot and on the
road on railway vehicles, whether these are specific to these tasks (or other maintenance),
commercial vehicles. All these operations have in common that they are carried out in the
own infrastructure. Surveillance tasks that can be remotely controlled (such as knowing the
occupation of a track circuit) are not the subject of the present study.
Each of the subsystems that compose the railway system is analysed, in order to ascertain
the operations that can be carried out by satellites. In the infrastructure subsystem1, we
distinguish the track from the platform. The first includes the following elements: rails,
sleepers, fastenings, track foundation (ballast and sub-ballast), or concrete slabs, as well as
other devices that are placed on them: diversions, escapes, sleepers, expansion devices, etc. In
the second, we include the different types of civil works that we find in a railway infrastructure:
natural platform (embankments, trenches, form layer, etc.) and artificial platform (tunnels and
viaducts), as well as their drainage systems. The surveillance and inspection operations in this
subsystem focus on the following:

In the case of the track, it is interesting to know both the state of the elements and the
geometric quality of the elements.

• In the case of the condition of the elements, the main operations are the control of the rails
(wear and internal state by ultrasonic auscultation), as well as control of the condition of
the materials (ballast, sleepers, joints, fastenings, welds, Track, etc.).
• In relation to the geometric quality, it is determined by five parameters: leveling, longitudinal
and transverse, alignment, gauge and warpage (UNE-EN 13.848-1: 2004). Measurement of
geometric quality is a way of measuring the state of the set, as it is influenced by the
state of the track elements themselves and by the underlying support structures (track
foundation and platform).
Regarding the platform, monitoring operations depend on the type of element. In embankments
and trenches, movements are sought, paying special attention to the blocks that can be
detached and fall on the track in excavation zones.

In relation to the condition of the elements, the following specific aspects of certain elements
should be indicated:

• Ballast: it is necessary to verify the possible contamination of the ballast. The contamination
is the ballast dust that stems from its crushing, and which is characterized by the whitish
colour that appears in the surface of the ballast layer. Other parameters to check are the
dimensions of the layer, the slopes, the ballast shoulder, the amount of existing ballast and
the presence of vegetation.
• Sleepers: the maintenance operations consist on checking that are no cracks, and that no

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