On Britain's older railways, replacing rotting timber sleepers is a constant problem. Adrian Greeman reports on machines that make the job easier.
Along with wholesale track replacement and renewal, 'spot resleepering' has long been used to extend route life. This involves inspecting for and then taking out damaged and rotting sleepers and slotting in new ones. But it is a slow and awkward operation done manually by work crews.
Now a set of rail-mounted machines and attachments for existing rail/road vehicles (RRVs), made by Geismar in Germany, is making the job easier and faster. The gadgets - including ballast looseners and removers, a sleeper changer, drills and fastening fixers and a 'mini-tamper' - work with existing machines to form a mobile production train along the track.
Since Network Rail bought a set of the machines last year, it has been working with Mowlem Railways to run continuing practical trials at various locations around the UK. Recently a second set of attachments was added, and so pleased is Network Rail with results that it is likely to buy a third.
'There are large-scale track renewal machines in the US and Europe and we have some for major lines, ' says Network Rail senior plant development manager Farida Jarvis. 'But many older UK lines have constraints like tight curves, low bridges and a limited loading gauge.
'These machines, which are small and work in a sequence, are much more flexible.'
She adds that the latest models can give a line an extra 7-15 years of operation.
The devices are being made available to Mowlem for use on a number of contracts, typically upgrading stretches of rural track. A recent job was near Boston in Lincolnshire, and there are several projects under way in Devon and Cornwall. In future this 'heavy maintenance' - rather than capital work - may be brought in house, but nothing is yet decided.
Meanwhile, some Mowlem crews have had special training on the machine techniques. The firm also supplies some of its own more standard road/rail equipment to form the work 'caravan' of men and machines.
The Lincolnshire job was typical; over about two weeks the 24-man crew worked night shifts with seven-hour line possessions starting at 11pm.
'That is still quite tight, ' says Mowlem Rail manager Maurice Chapman 'because you need an hour to set up and an hour to pack away, so you only have five hours of real effort.'
Machines are normally stored between possessions in a local siding, although this is not always possible, he says.
The process begins with a Komatsu RRV excavator and two trailers to distribute new sleepers. Then comes a fastenings remover, usually for spikes or nut and bolts.
'This can be awkward because so many different types have been used over the years and they are often corroded or jammed, ' says Chapman. ' Occasionally they must be drilled out.'
First of the new machines is the ballast crib attachment, which has blades to dig in around the front of the sleeper and behind it, loosening and then scraping the stones sideways.
The principle of the operation is selective removal of sleepers without damaging the existing track geometry, so a space has to be made to push the sleeper down and forwards.
'We must not disturb the ballast actually under the sleeper - 'the stool', ' Chapman explains.
'And we are limited to removing no more than one sleeper in three to maintain track alignment, ' he continues. 'If there is a cluster of bad ones - which is likely because they are often found in wet spots, for example - we have to do several passes.'
The key machine is the Geismar sleeper remover, which comes next, grabbing the timber and sliding it out sideways. It is just as adept at pushing a new one back in. The only difficulty is at platforms or steep cuttings where there is too little room to push out the timber.
Next the track is set and the sleeper fixed using the gauging and fastening machine. This puts the sleeper into position and ensures the rail width is correct before drilling holes and inserting the fixings.
'We use on-site drilling because slight 'gauge spread' or creep within acceptable limits is normal on older lines: if this has happened a replacement sleeper must be adjusted to the overall run of the rails, ' Jarvis explains. 'So the fixings point can vary, which a pre-drilled sleeper would not allow for.'
Final touches are to replace ballast - done with a standard road/rail excavator - and then tamp it down using a special 'mini-tamper'.
'This just does the compacting.
Unlike the big tampers, it does not lift and align the track simultaneously, ' explains Chapman.
A little tidying up is left. The old sleepers have to be collected and a 'ballast brush' is run over to leave everything clean.
Chapman says he can manage around 25 sleepers per hour of actual working - 125 to 140 in a night shift, say - although more can be done with longer possessions when it is possible to leave track in various halfcompleted stages and continue on the next shift.