George Stephenson, Engineer for the Maryport and Carlisle Railway, reported that the cost of construction would be low as the level nature of the countryside did not require expensive engineering works.
One exception was the 57 metre long, three span Cummersdale viaduct which spans the River Caldew at a 52° skew two miles south of Carlisle.
This viaduct was the most significant structure on the railway which was initially opened as a single line in 1845 to carry coal from the Cumbrian coalfields to Carlisle and Maryport docks. The current twin track viaduct structure was a 1910 upgrade.
Although the coal mines are long gone, the line still carries fuel with oil trains to BP’s Dalston oil depot and nuclear flasks from Sellafield. So the Christmas disruptive possession for the refurbishment of Cummersdale Viaduct was timed to end at 02:50 on 28 December, to maintain freight paths to and from Dalston.
£1 million life extension
Network Rail’s Cummersdale viaduct project is a £1million design and build package of work to renew the deck, install waterproofing and drainage, grit blast and paint the steel riveted-plate main girders and provide scour protection. The principal contractor is May Gurney and the contractor’s designer is Pell Frischmann.
Environmental support was provided by JBA Consulting which undertook the baseline ecology and bat emergence surveys as well as giving advice on the river’s Special Area of Conservation (SAC) designation for crayfish and salmonid fish.
This work identified that white-clawed crayfish were not present in the Caldew branch of the SAC and, with the agreement of the Environmental Agency and Natural England, JBA proposed that this species did not require a specific survey.
However, the presence of salmonid fish in the Caldew meant that any in-stream work could not be carried out during the spawning season – between the end of September 2011 and June 2012. Early identification of the environmental constraints at the site and the careful timing of works meant that no delays were experienced to the project in spite of its location within a SAC.
Work started on site in September. Vegetation within 3 metres of the bridge was cleared. Scaffolding to support a crash deck under the bridge and encapsulation around the main girders had to be completed before the spawning season started.
Grit blasting and painting of the girders was undertaken by Jack Tighe. After this was completed, rectangular holes were cut into the encapsulation to provide ventilation and also a sneak preview of the new Holly Green paint finish which replaced the previous light green.
The Christmas Possession
The largest item of work was the planned redecking, waterproofing and provision of a drainage system during a 77 hour disruptive possession from 21:00 on Christmas Eve to 02:50 on 28 December.
This work was entrusted to Stobart Rail under May Gurney’s supervision. The life-expired timber decking was to be replaced with 46 steel units fabricated by Britcon (Scunthorpe) Ltd. These units, typically 2.7m long x 3.4m wide x 0.75m high, have an L-shaped cross section to give improved ballast retention.
Christmas in Carlisle was mild and mainly dry, but with 30 mph winds. Although this would have prevented the use of cranes, it did not disrupt the Cummersdale work which only required low lifts by on-track plant. To enable these to work from the adjacent line, the redecking was planned to be carried out one track at a time with the Up line removed first.
The 120 foot long, jointed track panels on the bridge were cut into 60 foot panels and removed from the bridge by a tandem lift.
Once ballast had been cleared, the timber decking was removed by 360° excavators, enabling the tops of the steel girders to be treated prior to installation of the steel deck units. The crash deck and encapsulation prevented any contamination of the river during this work.
By the early hours of Boxing Day morning the Up side of the bridge was ready for its new steel deck units. However, during marking out with the bridge dismantled, it was found that some units did not fit into the stonework at the end of the bridge. This unforeseen problem was resolved on site, but the resultant delay was greater than the possession contingency time.
As required by Network Rail standards, possession plans must include hold points beyond which work should not proceed unless the expected progress has been achieved. The Cummersdale viaduct possession had two hold points, the lifting of the Up line and the lifting of the Down line.
As the criteria for the second hold point had not been met, Network Rail’s standard NR/L3/INI/CP0064 “Delivering Work within Possessions” required that the work could not proceed beyond the second hold point.
As a result, at 10:00 on Boxing Day morning, the decision was taken not to commence the replacement of the second half of the deck and Network Rail agreed that the timber deck under the Down line could be replaced in a future disruptive possession.
Whilst this was understandably frustrating to those on site, this instruction ensured there was no risk to the handback time for the possession of 02:50 on 28 December.
The Site Construction Manager considers that the experience gained from the Up line deck replacement will be useful when the time comes to replace the Down line deck. Time consuming marking out will not be required as deck unit positioning will be determined by the units already in place under the Up line.
Environment Agency restrictions on accessing the water during the salmon spawning season will determine when the scour protection works at Cummersdale viaduct can be finished, as the installation of riprap stone around the piers for scour protection cannot be undertaken until June 2012 – after the spawning season.
Completion of the bridge re-decking work will be dependent on May Gurney securing suitable levels of possession access to the route during 2012, which is normally restricted to Sunday mornings and Christmas Day/Boxing day.
During the period of the possession, the level of the River Caldew rose after a particularly heavy rainfall and the water was fast flowing, showing the challenge that the salmon face to swim upstream to lay their eggs. This also demonstrated the need for scour protection, and the difficulties associated with its installation.
Functional and Unobtrusive
Network Rail’s Scheme Project Manager, Chris Chatfield, commented, “The maintenance and re-use of the existing main girders, combined with the installation of new waterproofed steel deck units, optimises the most efficient blend of old and new materials to secure the working life of the structure over the long term.”
The steel-plate Cummersdale Viaduct is only a few metres above the river, has no graceful curves or tall piers, and so is unlikely to attract much attention from those who walk beneath it on the Cumbria Way long-distance footpath. As one of the project team said, “It is not a thing of beauty, but it is functional and looks right to me”.
However, with the completion of its refurbishment the viaduct will continue to be functional for many years and, resplendent in its new Holly Green coating, it might even attract more glances from those who walk or cycle under it.
This article was written following a site visit to the viaduct for which May Gurney’s assistance is greatly appreciated.