Dynamic monitoring of railway track displacement using an optical system

Abstract

With the increases in traffic, axle loads and travelling speed, the dynamic monitoring of railway tracks and structures is becoming more and more important to ensure a high level of safety and comfort. This situation is particularly critical at transition zones where rapid changes of track stiffness occur. This paper presents a contactless system to measure track displacements and its application in an embankment/underpass transition zone, located on the Northern line of the Portuguese railway network where the Alfa Pendular tilting train travels at a maximum speed of 220 km/h. The system is based on a diode laser module and a position sensitive detector (PSD). The PSD receives the laser beam emission and the detection of the centre of gravity of the beam spotlight on the PSD area enables the calculation of the displacement. Before field application, static and dynamic laboratory validation tests were performed in order to evaluate the system performance for different laser to PSD distances, and an accuracy of 0.01 mm was achieved using data acquisition rates of up to 15 kHz. The optical measuring system proved to be an efficient and flexible way to measure absolute and relative rail displacements in the field, enabling the detection of track deformability differences along the transition zone, even for the passage of trains at high speed (220 km/h).

Transition zones to railway bridges: Track measurements and numerical modelling

“…We have reported similar results of increasing stiffness at the approach to an underpass, regarding the same railway line [15]. The increase of the track stiffness at the approach to structures has also been reported in other field studies [16,19,20].…”

“…2): (i) shear deformations of the rail web, using strain gauges to calculate the dynamic wheel loads and the reaction force at the rail seat portion of the sleeper (Fig. 5a); (ii) rail seat loads on the rail pads, using fibre optic sensors; (iii) rail vertical displacements at positions 1-4, using four contactless systems that comprise a LASER and a Position Sensitive Detector (PSD) [16] ( Fig. 5b); (iv) rail-sleeper vertical relative displacement, using a LVDT (Fig.…”

Review of Trackside Monitoring Solutions: From Strain Gages to Optical Fibre Sensors

“…Optical detection systems can also be used for evaluating the track deflection. For instance, Pinto et al [ 7 ] showed that it is possible to obtain a reasonable accuracy of measuring absolute and relative rail displacements using a position sensitive detector integrated in a continuous monitoring system. A large body of work has been, and continues to be undertaken and this paper will present some interesting and reliable optical fibre-based detection systems.…”

Non-destructive Assessment and Health Monitoring of Railway Infrastructures

“…Very rapid stiffness leaps between different materials are in fact a matter of concern for scientists and infrastructure managers. It was reported that embankment/bridge transition zones may require five times higher maintenance frequency and cause two times higher cost compared to a plain track (Pinto et al 2015). These local issues cause variations of the interaction forces between the trains and the track, leading to fragmentation of the underlying ballast, or to plastic deformations in subgrades and, eventually, to differential settlements (Hunt 2005).…”