feature
Grahame Taylor reports...
Raising
the roof
in Chorley
cutting
when work had to be done to enable the
Pendolinos to travel through the route. To
improve vertical clearances, the only way
was down. A 'ballast scrape' gave the
correct headroom and allowed the
diversions to go ahead, but the track
suffered. With a formation failure
developing it was not possible to
maintain line speed of 75mph and as a
consequence a 20mph Temporary Speed
Restriction (TSR) was imposed in August
2007.
'Feel-better' engineering completely out of sight of the public. Out The local maintainers tried to keep it
The Grade II listed 'flying arches' at in the open air to the north however, the going, but there was always the threat of
Chorley are – or at least were – a line passes between fairly ordinary stone a 5mph TSR and even line closure. This is
mystery. They were delicate compared retaining walls. a very busy route linking Manchester and
with the usual engineering associated There are historic hints that something – the Airport with the Northwest of England
with the Victorian railway age. At just 400 either the tunnel or the retaining wall – and Scotland.
mm across they were hardly wide enough collapsed. Perhaps this is why the flying
to walk over – not that that would been a arches or buttresses were constructed. Risks overhead
very sensible thing to do because they Whether they were temporary works that Stephen Townley works as a Scheme
spanned between retaining wall sides 4m have been retained or were put in as part Project Manager for Network Rail's
above the running lines. of the original design is not clear – Infrastructure Investment division who,
It's not that clear why they were built. although some clues (revealed later in along with their Civils Framework
When the line between Euxton this article) were found when the arches contractor Birse Rail, were given the job
(pronounced Exton) junction, south of were dismantled. Undoubtedly, the of rescuing the situation following the
Preston, was built to link the northwest buttresses made someone 'feel better.' imposition of the 20 mph TSR. Primarily a
with Bolton and Manchester, the track and formation problem, the solution
engineers had to drive through high Deteriorating track soon involved the retaining walls and the
ground just north of Chorley. The ground Generations of engineers have accepted arches. Key to the problem was drainage
conditions were – and still are – poor. that the arches had to be there. As a – getting rid of the water.
Glacial till, running sands and a high result, they have presented vertical The existing six foot drain was nearly
water table. Two major structures were clearance problems over the years and derelict with a limited capacity and had to
involved. To the south, Chorley tunnel the result of this has been that the track be replaced. Nothing had been disturbed
was built to almost cathedral quality has not been lifted out of the mud. The through the area since the railway had
standards. The stonework – even within track has had a history of problems with been built and so there was unease about
the tunnel – is dressed and beautifully defective drainage – not helped by the how the whole structural system would
bedded with hairline joints. It is a mystery water table being almost at sleeper level. react to such major disturbance. There
why such care should have been taken on Track maintenance issues came to a were too many uncertainties for comfort.
this one tunnel when all this quality is head after the 2004 WCML diversions Designers Scott Wilson were
october 2008 | the rail engineer | 41
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