3) Rail Tracks: Track monitoring systems also play a vital
role in maintaining the safety of the railways. Monitoring
bridges and tunnels (discussed in the previous paragraphs) uses
sensors to identify and analyze defects (cracking and displacement)
in large structures. In contrast, track monitoring involves
identifying and analyzing defects in long narrow metal rails.
Tracks can crack and displace like bridges but also twist and
tilt (incline). Hence, track monitoring can vary from detecting
settlement and twist such as that caused by nearby tunneling
or excavation [112]; to measuring the forces exerted by train
wheels on the tracks; to monitoring the development of cracks
and structural flaws as trains pass and over the longer term.
Durham Geo Slope Indicator Company (DGSIC) [112] and
Aboelela et al. [1] analyzed the track movements (shift) over
time particularly where nearby construction work may affect
the track or where track passes through vulnerable areas such
as regions prone to landslides. Aboelela et al. [1] mounted
inclinometers parallel with the tracks directly on the sleepers
or in the ballast with continuous tensioned rails to monitor tilt.
Likewise, DGSIC [112] mounted inclinometers parallel with
the tracks to measure settlement. They also mounted inclinometers
perpendicular to the track (on the ties) to monitor twist.
Aboelela et al. [1] also plan to use inclinometers to monitor ties
to detect broken ties or sabotage.