It was previously a challenge for London Underground to produce the right type of sleeper that could guide the track around curves of less than 200 metre radius and still ensure Tube trains stayed on track.
Sleepers designed for curves were previously made of timber, which tends to shrink over time and therefore can affect the gauge of the track. London Underground wanted a longer term solution and after 12 months of development work with Cemex, a new sleeper for curves is now available.
Cemex says that the main challenge was how to attach the cast iron base plate to the sleeper. This would normally be done by casting plastic dowels into the concrete to allow the base plate to be bolted down. Analysis by Durham University highlighted complications when using standard attachment methods, related to the forces in pre-stressed concrete that may induce cracking.
Replacement of plastic inserts normally used for attachment of conductor pots by steel inserts and reinforcement around the plastic dowells, adopted from industry practice in Germany, has significantly reduced the risk of any possible cracking.
The Cemex Rail Solutions factory in Somercotes, Derbyshire, is now producing three variants of the rail sleeper, with two further ones in the pipeline.