Self-levelling railway sleepers could cut disruption and maintenance costs
Heriot-Watt engineers, working with colleagues at the University of Leeds and across Europe, have designed and tested a new type of self-levelling railway sleeper to tackle the long-standing problem of transition zones on the rail network.
They say the innovation could reduce maintenance work, cut costs, improve passenger comfort and lower the track’s environmental footprint.
The sleeper is manufactured from recycled plastic, helping to reduce demand for virgin materials.
It’s not just another small fix: it’s a sleeper that can correct minor faults on its own, so it needs less manual maintenance. As well as reducing maintenance, the sleeper is manufactured from recycled plastic, giving waste material a long-term, high-value use in railway infrastructure.
It system was tested at Heriot-Watt's purpose-built railway test track, the largest facility of its kind in the UK.
The facility replicates the loads generated by high-speed trains and can simulate decades of operation on major rail lines, enabling researchers to evaluate long-term performance under controlled laboratory conditions.
Why transition zones are a problem
Transition zones are sections of track where stiffness changes abruptly, such as where an embankment meets a bridge or tunnel.
The spots are among the most expensive and difficult sections of railway to maintain.
Dr Ahmet Furkan Esen, from the Heriot-Watt University’s School of Energy, Geoscience, Infrastructure and Society, said: “Over time, the softer ground settles more than the structure, creating small gaps under the sleepers, the rectangular supports that hold rails in place.
“Hanging sleepers then no longer sit firmly on the ballast, which is the crushed stone layer beneath the track.
“As trains pass over them, loads are unevenly distributed, increasing wear on rails, sleepers and ballast.
“The result is more frequent maintenance, speed restrictions and passenger discomfort.
“Millions are spent each year across Europe’s rail network to maintain transition zones, and it’s been a persistent engineering challenge.”
How the self-levelling sleeper works
The team has been developing the self-levelling sleeper for four years and reported progress in the journal Transportation Geotechnics.
Dr Esen said: “It works a bit like a self-adjusting jack.
“If the ground underneath settles and a gap opens up beneath the sleeper, a mechanism inside it lowers the sleeper base down to close the gap automatically, without anyone needing to come out and fix it.
"This could be a real step-change in how we look after transition zones.
“It’s not just another small fix: it’s a sleeper that can correct minor faults on its own, so it needs less manual maintenance."
"As well as reducing maintenance, the sleeper is manufactured from recycled plastic, giving waste material a long-term, high-value use in railway infrastructure.
"That helps support a more circular economy for the rail industry while reducing reliance on virgin raw materials."
Full-scale testing at Heriot-Watt
The team tested full-size prototypes at Heriot-Watt’s specialist facility to determine whether it could work in realistic conditions.
Dr Esen from Heriot-Watt said: “Our test track bed allows us to simulate the long-term effects of high-speed traffic and decades of operation on major lines.
“Over three days, we ran 600,000 loading cycles, applying forces of up to 41.7kN per rail seat, equivalent to a 17-tonne axle load, to mimic the forces generated by operational and high-speed rail traffic.
“We also introduced carefully controlled gaps beneath the sleepers to simulate progressive ground settlement, just as would happen in a real-life railway track.”
“Sensors embedded within the ballast measured load transfer and pressure distribution throughout the tests.”
The results were positive.
“We demonstrated that the self-levelling mechanisms activated once small voids began to form, and restored contact between the sleeper and ballast.
“Over the course of the test, it compensated for gaps of up to 40mm while maintaining stable load paths beneath the rails, preventing the damaging impact forces typically associated with hanging sleepers.
“We’ve proved this is a realistic infrastructure solution for railways. It has been designed to fit standard railway tracks and to be compatible with widely used fastening systems and maintenance practices.”
Dr Esen said: “We need to further refine and test the sleepers, but the results are extremely promising and demonstrate our technology’s practical potential.
“Our self-levelling sleepers could help rail operators maintain smoother tracks, reduce disruption and lower whole life maintenance costs, particularly in troublesome transition zones.”
The research was funded by the Shift2Rail Joint Undertaking under the European Union's Horizon 2020 programme (grant agreement No. 101014571), as part of the IN2ZONE project. Find out more at https://in2zone.eu/
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