Vibration Attenuation at Rail Joints through under Sleeper Pads

Modern railway tracks require electrification to power the trains and signaling systems to detect near real-time location of trains on railway networks. Such systems require the rail to carry and return the residual electricity back to substation, while enable signals to transfer within a track circuit. This track circuit requires rail joints to divide and insulate each loop of the circuit. Such the rail joints often generate impact transient dynamics to track systems. This paper presents the filed investigation into the vibration attenuation characteristic of under sleeper pads (USPs), which are the component installed under the concrete sleepers generally to improve railway track resilience. The field trial is aimed at mitigating rail joint impacts in a heavy haul track under mixed traffics. 'Big Data', obtained from both the track inspection vehicle and the sensors installed on tracks, demonstrate that track surface quality (top) of the section was improved after the track reconstruction. Fourier analysis results showed that the track surface (or vertical deviation) tends to deform at larger displacement amplitude and resonates at a lower wavelength of track roughness. Interestingly, the operational pass-by vibration measurements show that the USPs has resulted in an increased vibration of both rail and sleeper with USPs. Although the studies have found that the sleepers with USPs tend to have lesser flexures, the field data also confirms that a railway track with USPs could experience a large amplitude vibration, especially when excited by a high-frequency impact force. These dynamic behaviours imply that the use of soft to moderate USP could potentially induce dilation of ballast whilst the use of hard USP may reduce sleeper-ballast friction. In the end, these could then weaken lateral track stability over time.