maintain the bridge to ensure
trains are able to run at line
speed, which is 110 mph, in
line with its ‘Putting Passengers
First’ policy, but they knew
that this could not last. The
timber deck continued to
deteriorate, ballast was being
lost and, with the advent of
electrification, and new rolling
stock with different breaking
and accelerating characteristics,
the forces on the superstructure
were becoming unacceptable.
It was decided that the bridge
needed to be replaced.
Tony Gee & Partners were
invited by Network Rail to
develop options for replacing
the bridge. An emerging initial
plan was to construct a new
culvert structure within the
railway embankment to the
west of the underbridge. A
new river channel would then
have to be excavated, offering
a permanent diversion of the
river away from the current
underbridge, under the new
culvert.
The new river channel
would be approximately
135 metres in length and
would take water from the
existing channel, at a point
approximately 50 metres
upstream of the current
underbridge, and convey it
northwards through the new
culvert and then eastwards
before connecting back into
the existing river channel
immediately downstream of
the underbridge. This would
then enable the underbridge
to be demolished, and the
railway embankment filled in.Environmental concerns
It was a good plan, but close
scrutiny by the Environment
Agency raised serious concerns
about changing the flow of
the river as it could lead to
a change in the flood plain
which could affect local
communities and also local
wildlife habitats. There were
too many unknowns, and the
estimated cost of the work alsoexceeded budget allocation,
so, eventually, the proposal was
dropped.
Therefore, it was agreed that
the old bridge would have to
be replaced insitu. However,
the location with its restricted
access points, woodland copses
and sodden spongy ground, the
length of bridge spans involved,
as well as the radius for lifts
required, adjacent to the
bridge, meant that engineers
had to get their thinking caps
on. Network Rail’s project
engineer Matthew Roberts and
programme manager Scott
Pillinger told Rail Engineer what
happened next.
A new plan and design
emerged and the principal
contractor appointed for the
£4 million contract. They had
sixteen weeks to get the site
ready, as the essential work to
replace the bridge was planned
to start at 00:10 on Saturday
4 May and finish at 05:10 on
Tuesday 7 May 2019. It was
decided that the bridge had
to be assembled on site in four
sections. Tony Gee & Partners
designed eight Z-type steel
main girders plus cross girders,
and the decking would be a
reinforced concrete design.
The steelwork was fabricated
in Wigan by Time DMG.
This included manufacturing
1.5-metre-deep Z type girders
and associated cross girders
that would be transported toFE ATURE 69