Repair and maintenance of a historic Portsmouth bridge is proving the wider benefits of a blockade approach to construction works.
Network Rail engineers are taking a fresh approach to planning essential maintenance and improvements to Landport Viaduct in Portsmouth.
The steel and cast iron Victorian viaduct between Portsmouth & Southsea Station and Portsmouth Harbour Station supports two platforms for Southwestern, Southern and Great Western trains.
Work to strengthen the ageing structure, which was built in 1876, will ensure it can support train services for another 60 years.
Between 18 and 24 January, the line from Portsmouth & Southsea station to Portsmouth Harbour was closed, allowing the team to start work on strengthening 10 of the 129m long structure’s 17 spans.
The remaining seven spans will be strengthened during a blockade planned for next year.
Network Rail senior asset manager Mark Evans says the team – which includes contractor Osborne – is approaching the £5.3M project across two defined periods, reflecting a split in the structure’s requirements.
“Even though all 17 spans are next to each other, they’re in two different scenarios. Spans seven to 17 pass through the station structure and they are, for the most part, pretty well protected by Portsmouth & Southsea Station,” he explains. “It’s a coastal area and a metallic structure, so it can suffer pretty harshly from the marine environment with that sea air being blown in from the coast. Spans one to six are far more exposed.”
The programme of work is complex, with the team undertaking various improvements and refurbishments concurrently.
“Once you’ve got all the staff mobilised there, it makes sense to get as much bang for your buck and use that as an opportunity to extend its life,” adds Evans.
One element that we try and improve on at every opportunity is to remove any inherent weaknesses or risks with structures
“One element that we try and improve on at every opportunity is to remove any inherent weaknesses or risks with structures – and a big one is timber. Quite a lot of our bridges have timber decking [which provides a safe access walkway for railway maintenance staff] and inherently that can suffer from decay and rot.”
Evans explains that the project has provided an opportunity to replace the timber decking boards with a more durable material. “It will be a form of plastic – we use a GRP [glass reinforced plastic], typically,” he says.
The new plastic decking has the dual benefit of alleviating the risk of deterioration associated with timber, as well as improving workforce safety. “Where we’ve got the opportunity to do that work, it is absolutely a priority,” says Evans.
Network Rail Wessex route director Mark Killick explains that the wider project would have normally taken a year to complete, with a series of weekend closures. “It would take a lot longer and, in a lot of cases, the quality of the work suffers because it’s so piecemeal,” he says.
Instead, adopting a blockade approach has boosted efficiency and allowed additional work to be completed on site.
“In terms of maximising the benefit of prolonged periods of access, it opens opportunities that you otherwise don’t see,” says Evans. For example, he explains, the track running across the viaduct is supported by longitudinal timbers which have also been incorporated into the refurbishment project.
“They are some of our most complex track support systems. They require a lot of inspection and maintenance for the same reasons as the timber decking,” says Evans.
“We won’t have the opportunity to replace them all but we are able to take out several in a row. We can then improve track alignment, which will improve ride quality, for example.
“If you are working across weekends or shorter accesses, that opportunity just doesn’t exist.”
In terms of maximising the benefit of prolonged periods of access, it opens opportunities that you otherwise don’t see
The site access in January was primarily for the viaduct work, but the team has also carried out
vital maintenance on the line from Cosham and Bedhampton to Portsmouth Harbour.
Engineers have undertaken track improvements and renewed timber rail supports – wheeltimbers – on the nearby St George’s bridge and the Portsbridge Creek crossing.
As well as providing an opportunity to deliver a broader programme of work, the blockade strategy also marks a shift in Network Rail’s focus on customer experience.
“There’s a lot of planning in advance and communicating to passengers around what the alternative routes will be. We make sure we’re really thinking about how passengers will travel around the engineering work we’re doing, rather than just focusing on the engineering work,” Killick says.
“Passengers will remember the experience much more than whether we painted and strengthened bits of infrastructure. It is about getting that balance between engineering and passenger experience.
“It’s not the way we might have done things in the past, but by focusing on passengers’ whole experience, what their options are and how we manage them through that has proved that this is the right way to do it.”
Killic admits that the pandemic and subsequent travel restrictions have made it easier to manage passenger flows, but he is confident the blockade strategy has helped to support improved efficiency across the wider project.
Killick says: “The more we deliver these [blockade strategies] in a successful way, really putting the passenger at the centre of what we need to do to deliver the engineering work, it builds a much more efficient way of working.”
During the interim between the two blockade periods, the team has moved onto other infrastructure projects in Network Rail’s pipeline. “We also continue developing the final details for spans one to six during this period,” says Evans.
Work on the remaining spans is scheduled to commence in January 2022.
Department of Civil Engineering https://www.ibu.edu.ba/department-of-civil-engineering/