Bridge reconstructed in Llantwit Major, Wales

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Once upon a time, there was a railway bridge in Llantwit Major that carried the two tracks of the Vale of Glamorgan line over a narrow residential single-lane carriageway. Originally constructed in 1896, Eagleswell Road underbridge had a span of 10.4 metres with a 45 degree skew.

The superstructure was typical of its era, comprising three simply-supported steel plate girders in half-through formation with steel traverse troughing. Unfortunately, it was no longer fit for purpose since it was unable to comply with the route availability loadings required for this line. Something had to be done to ensure that maximum use of the route was maintained for freight traffic.

One option considered was to repair and strengthen the bridge. However, this would have required closure of the line for removal of the track and ballast, allowing access to be gained to the structure’s central sections where some work would have to take place. Coupled with this, the bridge leaked like a sieve and re-waterproofing of the whole deck would be needed, along with grit blasting and repainting, to provide a new protective coating.

When considering the long-term overall costs involved, it became apparent that refurbishment would prove more expensive than reconstruction. It was estimated that further repair work would be required within 25 years and the total life of the refurbished bridge would only be 50 years. Network Rail had to consider not only the merit of this option but also the views of residents – this was a very cramped residential site and, whatever the chosen option, those living nearby would be exposed to considerable inconvenience and disruption.

Resident consultation

So the case was put to locals at a meeting, along with Network Rail’s preferred option to replace the bridge, offering a 25-year maintenance-free period along with a design life of at least 120 years. Given that the existing structure was 114 years old, it was agreed by all that replacement was the best option.

As a consequence, in January 2010, Carillion was invited to design and build the new bridge. The value of the work was in the order of £750,000 and the plan was to install it during a 44½-hour possession over the Bonfire Night weekend in November 2010. Preliminary work would start in early October. A lengthy road closure was arranged with the local authorities, starting on 25th October and extending until 8th December. Clearly, this must have caused significant disruption for locals – it became an important aspect of the project and needed to be carefully handled.

The person responsible for managing this issue, as well as the smooth running of the overall venture, was Network Rail’s scheme project manger Deborah Elliott. She explained to me that not only did they have to deal with problems associated with noise and road access but, because of the very cramped site, a 500 tonne mobile hydraulic crane was needed with its outriggers founded in residents’ gardens. Fortunately, after careful consideration and negotiation, suitable and appropriate compensation was agreed with the home owners.

There was one unexpected bonus that surprised Deborah. In the area around the site, the road is tree-lined, leafy and quite attractive. But many of these trees were on Network Rail land and would have impeded efficient working on the site so they had to be removed. However, instead of the expected resistance from residents, the team was greeted with thanks. At last natural sunlight could penetrate through to their gardens – a benefit they had not expected!

Reconstruction of bridge in Wales: crane
One-tonne dumpy bags of ballast are craned onto the bridge

Difficult crane positioning

The design of the new bridge superstructure consists of two independent steel and concrete composite decks, each carrying one track. New safe cess walkways were designed to cantilever off both sides – an improvement that removed the limited clearance hazard created by the old deck. These walkways also provide space below them for the service cables, bringing far better access for future maintenance.

The composite superstructure spans were manufactured by Wigan-based DMG Steelworkers and were transported to site by road. The 500 tonne crane provided by Baldwin Crane Hire was located at the north side of the site, straddling the precious shrubbery of one particular householder. Its positioning was critical as, no matter where the crane was located on the site, it would be required to lift loads at its maximum permissible limits.

The skill and expertise of the slingers were tested for each significant lift and the positioning of the outriggers had to be very carefully thought out before each one could begin. Deborah emphasised that the excellent relationships built with Carillion’s site agents, Mike Barton and Matt McKenzie, ensured that everything happened in a safe and compliant manner.

Fortunately, the existing abutments were still in very good condition. During the possession, they had to be broken down to a pre-determined level to enable two precast concrete cill beams to be installed. These were manufactured by Cornish Concrete Products, based in Truro, and also transported to site by road. The plan was to place the beams during the possession and this important operation happened without incident.

Drilling through granite

In order to accommodate holding-down bolts for each beam, five holes had to be drilled 3m into each abutment. Holemasters, the subcontractor carrying out the drilling, had estimated 30 minutes per hole although Carillion had built in a contingency to increase the time to 60 minutes. In reality, each one took nearly two hours. There was nothing wrong with the drilling process itself – that worked perfectly well. However the ground investigation previously carried out failed to locate a vein of granite rock behind the abutment, hence the delay. Finally the beams were bolted down and the new decks, with their robust Waterseal waterproofing system, were installed without further setbacks.

Fortunately, Carillion’s contingency reduced the programme delay to five hours and this was recovered by the diligent work of Paul Barry and Network Rail’s track replacement team who were responsible for reinstating the p-way and giving up the possession on time at the full linespeed of 50mph. This was a first for the route – convention being a 30/50mph hand-back speed.

To achieve the recovery, they started to assemble the track into panels within reach of the crane earlier than planned. The nearest location for gaining road-rail access was more than nine miles away so ballast was brought to site by road in one-tonne dumpy bags. These were lifted into position by crane and then split to release and spread the stone.

Reconstruction of new bridge in Wales
Reconstruction of new bridge in Wales

Deserving festive treat

So, the new bridge is in place. The route availability has been improved from RA5 to RA8 – a significant improvement for freight traffic. Local residents now have more sunlight entering their gardens and no longer suffer a deluge every time they walk under the bridge. They were compensated for the loss of access to their properties and treated to a spectacular show that would befit any Bonfire Night. Finally, in recognition of the additional disruption she experienced through the intrusion of the crane’s long outriggers, one lady received a Christmas hamper. An appropriate treat for a job well done by everyone and hopefully a bridge that will last for a long time to come.

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