DOUBTS HAVE emerged over the integrity of rail lines installed using the record breaking track laying machine operating on the West Coast Main Line.
The £12M machine was imported from Harsco Technologies in Columbia in the US and has has allowed contractor Jarvis to relay over 65km of track in the past year.
However, according to industry sources, new sleepers are laid in different locations to those they replace, so without remedial action much of the newly laid track could, in theory, start to suffer instability through sleeper movement.
The problem stems from the fact that the machine is only designed to disturb or scarify the top 50-60mm of ballast below the existing sleepers. The train then lays the new sleepers on the scarified ballast.
But ballast under the new sleepers will not have had the same applied loading as the sections from where the existing sleepers were taken. This means it will recover and spread at different rates - a phenomenon known as ballast memory.
It is understood that the problem can be solved if the track is then re-ballasted within a few months before significant movement occurs. The time scale for reballasting depends on the original condition of the ballast and is in the region of a few months.
A spokesman for the machine manufacturer said it had held numerous discussions with Railtrack about breaking up and homogenising the ballast, but felt that although it was a problem in theory, it would not prove to be a fault in practice.
A Railtrack spokesman confirmed that theoretically there was an issue, but it had not proved a problem on the network. He also confirmed that Railtrack had been looking at different types of track laying machines for a new 'second squadron'.
There is a preference for a set up that would not require the 'caravan' of trains which now have to follow the track laying machine, including a clipping machine and tamper. The spokesman said the network operator wanted a machine which would perform all the track laying tasks in one go and left a completed track at the site.
It is also understood that problems have been encountered with the automatic restressing facility on the track laying machine.
This system uses propane gas powered heaters on the track to reach the required stressing temperature. But no Health & Safety Executive certification has been attained for the computerised arrangement and the system has to be operated manually.
The track laying machine has also encountered problems moving surplus ballast from the track in front of it.
It was designed to work with ballast that was flush with the top of the existing sleepers, with a shoulder at either side. In reality there is much more ballast around the sleepers, and the machine has struggled to push the additional stone out of the way.
Excavating machines have been brought in to work in front of the machine and remove additional ballast.
One maintenance contractor has complained that the additional ballast is being deposited on railway infrastructure, such as cable troughs at the side of the track. Complaints have also been made that rail taken out by the machine was left at the trackside, blocking inspection boxes and trackside equipment.
However, there is no doubt that the machine has helped get the West Coast Route Modernisation programme back on track.
Earlier this month the machine broke its own production record for an eight hour night time possession laying 564m. In a weekend possession last month the machine relaid nearly 2.2km of track.