INTRO: Almost half the new sleepers being installed on Railtrack’s network could soon be steel. Richard Hope reports on a quiet revolution driven by major savings in materials handling and the volume of new ballast needed
RAILTRACK IS currently installing around 600000 sleepers annually on its network, which totals 32000 track-km. That number is certain to increase. A major project starting this year will see 460track-km completely renewed over two years on the West Coast Main Line between London and Crewe to permit 200 km/h running from May 2002, and 225 km/h from May 2005. This task alone will require 700000 concrete sleepers. It will also see the first significant quantity of 60 kg/m rail laid by Railtrack, marking a switch away from the 56 kg/m rail that British Rail adopted as standard in the 1960s.
Meanwhile, out of the limelight on secondary routes another quiet revolution has been taking place almost unnoticed: steel sleepers instead of concrete are increasingly being used when relaying takes place. From being an oddity subject to occasional trials on the national network prior to the 1980s, sales to British Rail and then Railtrack have increased tenfold in the 1990s (Fig 1).
Steel sleepers have been around for a long time. Their use is traditionally associated with light axleload lines in tropical zones such as Africa and South America, where timber sleepers may be subject to attack by termites. The absence of local timber is another factor. The Hedjaz Railway, completed 90 years ago through treeless desert between Damascus and Medina, was laid entirely on steel sleepers. In Syria and Jordan, where many remain in use, they have suffered little corrosion in the dry atmosphere.
At the other end of the scale, steel has been used on heavy haul lines in Western Australia and North America, with nominal axleloads ranging up to 35 tonnes - and even 40 tonnes when the effect of variable loading is taken into account.
Experience has been mixed, especially on curves when earlier designs suffered from low resistance to lateral forces, allowing the track to move. Lugs pressed out of the sleeper to hold the rail to gauge proved to be a point of weakness, again in curves where lateral forces are highest. This was overcome by using welded lugs.
In Europe, the use of steel sleepers is widespread, especially on secondary lines and industrial track, but overall they are far outnumbered by wood and concrete. Nonetheless, Corus Rail (formerly the division of British Steel rolling rail at Workington in the north of England) has supplied 20000 annually to Switzerland for some years.
Design from first principles
In Britain, the Great Western Railway started using steel sleepers in the 1930s, but they were not available during the Second World War. BR later adopted concrete as standard, but steel was used for a trial length of nearly 3 km on the Hope Valley route between Sheffield and Manchester in the early 1980s. Once again, this suffered from poor lateral resistance, but the experience led to the design using computer modelling of a range of steel sleepers for main line use, as opposed to low speed industrial track.
It was around this time that BR decided to create business sectors, and allocate responsibility for the infrastructure according to the prime user. Regional Railways was allocated lines carrying the lowest gross tonnage - not long after the BR Board had been warned by its civil engineers that certain lines would have to close if the track was not relayed. This had resulted from a period of very low investment in the 1970s.
Pressure to economise intensified when government set tough subsidy reduction targets in the mid-1980s. BR Research and British Steel therefore embarked on a joint development programme in the belief that substantial economies could be achieved by using steel sleepers rather than continuing with concrete.
Modern steel sleepers are rolled as a continuous profiled trough section in the same mill that produces rail, and then cut to length. This allows the flat top forming the rail seat to be thicker than the sides, and a substantial beaded edge is formed which provides bending strength. Apart from the different rollers required to produce this shape, the main difference to producing rail is that ordinary structural steel can be used because a sleeper does not experience the high stresses that occur at the wheel-rail contact patch.
Using finite element analysis, the as-rolled sleeper cross-section was refined to distribute the metal more efficiently, providing extra strength and stiffness while retaining the low weight and ability to be stacked in bundles that provide one of steel’s great logistic advantages over concrete. The weight per linear metre of the Type 400 sleeper produced by Corus for Railtrack is 31 kg/m, which means that when shoulders for the Pandrol E-clip have been welded on, a sleeper weighing 80 kg can easily be handled by two men. It takes eight men using tongs to lift a concrete sleeper.
As a separate operation, the sleeper ends are formed in a press to increase lateral stability. For main line use, it was found that the best lateral resistance was obtained by spade ends. The Type 400 sleeper trough is splayed, with the end bent down until it is about 50mm below the beaded edges of the trough. When this sleeper is placed on a levelled ballast bed, it sits initially on the spade ends, but the passage of ballast trains soon forces the spades and beads into the ballast, partially filling the ’pod’ formed by the inverted trough and spade ends. The pod is then filled by tamping.
Insulated fastenings well tested
One reason why civil (and signal) engineers have traditionally viewed steel sleepers with suspicion has been a fear that fretting would destroy the pad or plastic inserts that insulate the rail from the fastening and sleeper, causing track circuits to fail.
The presumption that concrete has insulating properties that steel obviously does not is challenged by David Ventry, Railtrack’s Head of Track Asset Management. ’The reinforcing bars make concrete just as good a conductor for practical purposes’, he insists. ’We are looking to improve the insulation further, driven by the signal engineers, but the fact is we have now had steel sleepers in track circuited routes for many years without experiencing problems.’
Corus Rail’s Project Manager for steel sleepers, Dave Farrington, points out that last December Railtrack received the millionth Type 400 sleeper to be delivered since production for BR commenced in 1987, ’so there has been plenty of experience.’ In BR days they were mainly installed by Regional Railways in northwest England. Ventry says that after Railtrack took over in April 1994, the use of steel spread to freight and inter-city routes.
By far the biggest single relaying job to be completed in steel took place last November during a four-week blockade of the Settle & Carlisle line. For many years, the threat of closure hung over this hilly main line route to Scotland, which was seen by BR as redundant after electrification of the parallel West Coast Main Line was completed in 1974. The track was allowed to deteriorate, and when freight began to be routed this way after privatisation, derailments led to severe speed restrictions that crippled line capacity.
Some 24 km of track was relayed by Railtrack’s contractor First Engineering during the S&C blockade, using 36400 steel sleepers. Around 100000 tonnes of new ballast was required for the whole job, including sections of track that were just reballasted, with about 20000 tonnes placed in the resleepered sections. Drainage works brought the total cost to £18·2m.
The S&C project illustrated one of the ways in which savings can be made by using steel sleepers, even though they cost £35 compared to £30 for concrete. Their light weight means they can be dropped in bundles at the lineside and placed manually on the ballast bed instead of being brought in as part of a mechanised relaying process.
But the biggest economy from using steel lies in a drastically reduced requirement for new ballast. Unfortunately, this feature could not be exploited on the S&C because much of the line was ballasted with ash; this had to be excavated and removed so that fresh bottom ballast could be placed.
Ventry gained much personal experience of steel sleepers in BR days when he was Area Civil Engineer based in Manchester, and he gives two reasons why ballast is saved under normal conditions.
First, the ’underside’ of a steel sleeper is effectively the top of the pod. This is the level at which most of the vertical load is transmitted to the ballast, and starts to spread out in a cone before reaching the weaker formation material. The sleeper depth (ignoring the deeper end spades) is typically less than 100mm, only half the 200mm depth of an equivalent concrete sleeper. Railtrack’s current standards provide for 50mm less bottom ballast under steel sleepers compared to concrete or wood. Add this difference to the reduced sleeper depth, saving about 100mm of top ballast, and the total depth requirement becomes 150mm less for any given track standard.
Secondly, steel sleepers are more tolerant of poor ballast quality than concrete. ’In the majority of situations’, says Ventry, ’we do not need to reballast before the steel sleepers are put down. Only if the existing ballast is wet and severely fouled - particularly with clay - would we dig it out.’
The procedure is that after the old rails and sleepers have been removed, the existing ballast is scarified to level it out and remove the old sleeper pits. New steel sleepers are then placed by hand, the new continuously welded rails slewed into position on their seats and clipped down, and top ballast distributed. After the track has settled under a few trains, it is tamped to fill the pods and bring it to level. Further tamping will take place after a few weeks.
Ventry notes the importance of getting the alignment right when steel sleepers are put in place because the spade ends make it more difficult to slew them during tamping than would be the case with flat-bottomed sleepers. Otherwise, there is no particular problem about tamping them, although the stoneblowers acquired by Railtrack cannot be used.
Corus puts the total saving in ballast and handling costs (including disposal or cleaning of recovered material) at £37000/km, which is £24 per sleeper, based on the Type 400 and E-clip as currently used by Railtrack. Ventry believes the saving is much higher, putting the total cost of track replacement with steel at £275000/km compared with £470000/km for concrete, a remarkable 41% reduction.
Railtrack has now approved the Type 500 sleeper developed by Corus, which uses Pandrol’s Fastclip in place of the E-clip. These have performed well for over a year at the initial site in East Anglia.
The main advantage stems from that fact that clips, pads and insulators are installed in the factory where the sleeper is assembled and are not lying around loose at the relaying site. The clip is secured or released with a tool, but the insulating components remain captive.
Another change is the use of Huck bolts to secure the cast iron housing carrying the Fastclip to the sleeper.
Handling pads and clips is labour-intensive, and Corus suggests a further saving of £6000/km in relaying costs with Fastclip. Ventry says this saving is ’not yet visible to me’ because the saving accrues in the first instance to the relaying contractor.
Corus is developing Type 600 sleepers for use on high speed and heavy haul lines, and this is certainly of interest to Ventry. But Railtrack is also likely to extend the range of the 400 and 500 as confidence is gained. ’At the moment’, he says, ’the upper limit of our applications is around 10 million gross tonnes a year, but we have relatively few heavily-used routes in our network.’
A 1·6 km stretch of Type 400 sleepers has been in service since 1997 at Quintinshill on the West Coast Main Line north of Carlisle, where the line speed is 177 km/h. However, there is currently no intention to use steel during the WCML upgrade currently in progress.
Nevertheless, the potential is there with the Type 600 and Fastclip. Ventry ’wouldn’t argue against putting the 600 in higher speed lines, though not between London and Rugby’ (the most intensively used part of the WCML). He thinks the Type 600 is more likely to be adopted to meet the aspirations of English Welsh & Scottish Railway for 30 tonne axleloads. ’Steel sleepers have their uses, but they are not always going to be the optimum solution.’ They will not be used in 750V DC third-rail territory, for instance.
Corus accepts that steel may not be regarded as suitable in corrosive situations, such as close to the sea. However, Ventry points to a stretch of track laid at Harrington, just south of Workington, where the track is drenched in salt spray during rough weather. He does not consider that corrosion has been excessive here.
Finally, there is the issue of competition. Ventry says Corus cannot expect to be Railtrack’s sole supplier because ’it is more healthy to keep the market open and more competitive. We have already approved an American design of steel sleeper, but it’s a question of getting them at the right price. However, we do intend to buy some in order to evaluate them.’
CAPTION: Railtrack has been evaluating Type 400 steel sleepers on a 1·6 km stretch of the West Coast Main Line at Quintinshill, north of Carlisle, since 1997
CAPTION: Fig 1. Sales of steel sleepers by Corus Rail to British customers, predominantly BR and Railtrack, have increased tenfold in the last decade
CAPTION: Corus Rail has recently developed the Type 500 steel sleeper, which is designed to use Pandrol Fastclip rail fastenings; these sleepers are delivered complete with captive insulators
CAPTION: Major advantages claimed for steel sleepers are the ability to store and transport large volumes in stacks, and to drop bundles by the lineside for manual laying
CAPTION: First Engineering used 36 400 steel sleepers to relay 24 track-km of the Settle & Carlisle line during a four-week blockade last November
CAPTION: The West Coast Main Line test section at Quintinshill is heavily used by Virgin West Coast and Virgin CrossCountry inter-city services at speeds up to 177 km/h
Summary in French, German and Spanish
Steel sleepers invade concrete territory
Railtrack expects to buy more than 200000 steel sleepers this year for use on secondary routes, and the total could rise to the point where almost half of the new sleepers being laid are steel. For more than 30 years, virtually all track renewed by British Rail has been 56 kg/m rail on concrete sleepers. Railtrack is now satisfied that careful research leading to improved designs has overcome most of the drawbacks traditionally associated with steel, such as poor lateral stability. Richard Hope reports on a quiet revolution driven by major savings in materials handling and the volume of new ballast needed.
Les traverses en acier envahissent le territoire du béton
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Railtrack plant, dieses Jahr über 200000 Stahlschwellen für Nebenstrecken zu beschaffen, und es k