HomeRail NewsFour bridges One valley

Four bridges One valley

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Regular readers of the rail engineer will have read reports on many infrastructure projects carried out all around the country in a variety of terrains. They will be forgiven for thinking that, after meticulous planning, all projects go exactly to plan and are delivered “on time and under budget”.

Unfortunately, real life isn’t like that. Most projects do indeed go as planned, although they will all have their little quirks and snags which have to be addressed. However, occasionally the opposing team, made up of the gods, Mother Nature, gremlins, protected species and the weather, can conspire against the project team. That’s when the ability to think quickly, adapt plans and timescales and find suitable ‘real-time’ solutions is critical, as is the sharing of lessons learnt post project.

Picturesque Esk

One recent example of this was on Network Rail’s Esk Valley line in the North Yorkshire Moors, between Middlesbrough and Whitby. The River Esk meanders through the valley, criss-crossed by the railway. A series of six bridges were built in the area in 1864, all to a similar design, which comprised a series of brick arches over the valley and a metallic bridge over the river itself. The bridges were each constructed from two wrought iron main parapet girders with curved cast iron top flanges. Wrought iron cross girders spanned between the parapet girders supporting the track mounted on longitudinal timbers.

In 1926, a strengthening scheme installed a steel spine beam to the underside of the bridge decks along the bridge centre line. At various times since, each bridge has had additional strengthening added in the form of bracing struts and extra stiffening.

By 2012, one bridge was disused and another, on the North York Moors Railway (NYMR), had already been replaced in 2010. Now it was time to replace the other four, all of which are on Network Rail’s Esk Valley Line. As the route is regularly used by schoolchildren, the obvious best time was during holiday time. So arrangements were made to do the work 2-11 June, which was school half term.

Making plans

As is usual, plans were made by Network Rail and main contractor BAM Nuttall. AECOM were appointed to do the design work, and ecological and ground surveys were undertaken.

Access is a problem in that area. With hills as steep as 33% (that’s 1 in 3!), getting materials in and out would be difficult. All the major components were therefore planned to come in by rail, and the lifting work would use two Kirow rail cranes, one from Colas Rail and the other from Volker Rail. This significantly reduced the impact of the project on the surrounding environment.

Best practice was adopted from an earlier scheme – the replacement of NYMR’s bridge 30 in 2010, with a similar design principle adopted. All bridges would consist of two main steel girders braced together supporting a precast concrete segmental deck with walkways. Unlike the NYMR bridge, the beams would be of weathering steel, so there would be no need for future maintenance painting regimes.

Due to the locality of the bridges, they would be constructed in two pairs utilising the same principal resources. The main project compound would be at Carr End bridge (Structure 81), close to Glaisdale railway station, with Thorneywaite (76), 1144 yards further away, being the second of its pair. Four and a quarter miles away is Duck bridge (60), with Danby (58) 621 yards beyond that.

Setting up shop.

Neighbours close to the compound at Glaisdale were contacted and the team worked closely with them to try and mitigate the impact of the works. Unfortunately, they remained vocal in their opposition to what is a “once in a life time” project.

With everything in place, preparations could begin. Some of the brick arches, such as the small cattle bridge (Structure 59) between Danby and Duck, had to be shored up and strengthened with temporary propping to withstand the weight of the Kirows when carrying a load. Doing the same on the brick arches at Carr End closed the road, so that to drive between the site compound and Glaisdale station, just on the other side of the tracks, meant a detour of around five miles.

Materials came in by train, and the two Kirows arrived. A family of blue tits was found nesting in one of the bridge structures, but the chicks fledged three days before work was due to commence so there were no problems there.

Darned dipper – part 1

However, the project team weren’t so lucky when, two days before the possession, as scaffolding and netting were being installed, a dipper was found nesting deep within Carr End bridge. She was so far in, that the nest could not be seen from ground level at all. The only way to have spotted the nest would have been to stand waist-deep in the river itself.

Dippers are rounded, short-tailed birds which are noted for walking into and under water in search of food. They are not particularly rare – the RSPB believes that there are between 6,800 and 20,000 breeding pairs in the UK. However, their nests cannot be disturbed without a licence from Natural England. Given the bank holiday, this was going to take several days to procure. Network Rail and the BAM Nuttall project team reset their programme to minimise delay to Carr End and to start work on the other three bridges.

Making a start

Props were installed between the abutments, holding them apart and in place so that there was no danger of them collapsing inwards under the weight of a Kirow crane close to the edge. In addition, due to exceptionally poor ground conditions at Danby, embankments were stabilised under the high Kirow loading by placing fill material at the toe of the slopes.

Demolition contractors S Evans & Sons moved in, and the three other bridges started to come down. The old cast/wrought iron structures were cut free and lifted out by the Kirows, then moved to compounds where they were cut up and the pieces loaded into lorries. Some of the beams exceeded the carrying capacity of the Kirows so they were cut into smaller sections. Before that, strengthening angles were added to ensure girder stability was maintained even while the cuts were being made.

The bridge abutments were dug away, freeing the old 1926 spine beams which were similarly removed. More of the abutments were cut away, making room for new precast concrete impost units to be fitted. These imposts, together with the concrete bridge deck sections, were already on site having been manufactured by Macrete in Northern Ireland.

With the bridges removed, the Colas Kirow was land-locked between Danby and Duck. Careful planning had made sure that all the components were on site, and a large RRV excavator on the Middlesbrough side of Danby was utilised to undertake the excavations on that abutment.

Once sufficient material had been removed, a layer of semi-dry concrete was carefully levelled to within a couple of millimetres of the design requirement and the impost units lowered into place.

Several of the bridges had a high degree of skew. Danby had none, but Duck was 42°, Thorneywaite 52° and Carr End 57°. The impost units were designed to remove that skew, allowing the new beams and concrete deck sections to be regular in shape.

Darned dipper – Part 2

By Wednesday 6 June, all three bridges were out and work was continuing on the abutments. Natural England, having visited site, gave verbal consent to remove the dipper from Carr End, though physical removal could not take place until a formal licence was in place which took another 24 hours.

Once granted, the nest was immediately relocated, allowing work to start, though time taken to resolve the issue left the project requiring an extension to the original possession of around 24 to 48 hours.

Crane issues

Demolition got underway, and before long the old bridge deck was ready to be removed. When first lifted, the beams tilted, implying that they weren’t balanced. A short section was cut off to equalise things, and the lift started again. This time it tilted even more alarmingly the other way, causing the end of the lifting beam to hit the crane jib, breaking a metal conduit and damaging the wiring inside.

Work stopped while the wiring was repaired, which took twelve hours. Scheme project manager Darryl White himself found the vital missing fuse amongst the ballast to get the Kirow up and running. The only requirement now was to weld the conduit back to the main jib. Amazingly this was undertaken by a local mechanic who could have asked for the earth but only charged the magnificent sum of £20. Well worth the money!

Back in action, the Kirow removed the offending bridge beams and work on the abutments could begin.

But now there was another delay. The rain had been heavy for a few days, and as a result the water level in the river had risen. Even though the danger to the workforce had originally been assessed as minimal, with harnesses and life jackets utilised where required, by the weekend the river was in flood. HM Inspectors asked the project to suspend work while divers, boats and lifelines were acquired in case anyone should fall in the river. It was another day lost although, in view of the conditions, it was a sensible precaution.

Beams, section and hollow chambers

By now, the other three bridges were nearing completion. The spine beams for the new bridges had been made by Allerton Steel and delivered to site via train from AV Dawson’s yard in Middlesbrough. At Danby, the beams had been delivered to site already bolted together but it was decided that, as there was only one prop in this location, it would be safer to reduce the load and install the beams singly. The pre-assembled beam was unbolted, and each part installed separately. Some of the new beams were nearly 34m long and, to extend the reach of Kirow, these were installed with counterweights to offset the centre of gravity closer to the crane.

Once installed, the precast concrete deck sections were fitted. Resembling an upside-down top hat in section, track was relayed in the “crown” section, while the “brim” on either side formed the walkway. Each section had rectangular holes in the bottom, corresponding with shear studs on the beams that were grouted into place to stitch the concrete section to the steel beams and allow the section to act monothically. At each end of the bridge, a precast concrete step section gave access to the walkway, which was fitted with a handrail.

When each bridge was complete, the ballast and track could go back down, ready for tamping.

Meanwhile, there were more delays at Carr End. Once the bridge deck was up, it was discovered that the original abutments, as built, were hollow and made up of a number of chambers or voids. At some stage, probably during the fitting of the spine beam in 1926, these had been half filled with clay, which is what the trial coring had shown. However, they weren’t full, and would need to be, to support the Kirow installation loads. Fourteen lorry-loads of ready-mix concrete (80 cubic metres in total) had to be conjured up quickly.

Temperamental tampers

At Duck and Danby, tamper trouble saw the job completed with a 20mph speed restriction. A second tamp was organised through Network Rail NDS for Thorneywaite and Carr End, but unfortunately the tamper broke down again, with a complete new tamp required post possession.

Despite the challenges (of which there were many), the project was finally finished and the bridges handed back on Saturday 16 June, five days later than planned. On the following day, the bridges were crossed by the famous Sir Nigel Gresley A4 steam locomotive which was travelling to Grosmont to carry the Olympic torch on its journey through Yorkshire. That deadline had been another pressure to get the job completed.

So, a very relieved project team were pleased to be finished. Two follow up tamps would be required to restore the linespeed to 45mph (35 on Carr End but that is so close to Glaisdale Station that it is impossible to do that speed anyway) and these were carried out before the end of June.

Looking back

Darryl White reflected on a difficult few weeks. “I’m pleased all of the work was completed, as having to come back, more than likely during the winter, would have been particularly difficult. This was definitely the best outcome for everyone, putting the customer first. A return visit to complete Carr End would have taken longer than the five day overrun. You have to add into this the disruption to the locals for remobilising and demobilising and it’s probably saved at least another 3 months on site.

“Of course I’m disappointed that the works overran, but taking into consideration the challenges faced and the intense pressure that we, Network Rail and BAM Nuttall, were all under, I think we worked well together to see the job through to completion – it should be noted without any accidents or injury.”

Richard Allan, area director for the train operator Northern Rail, was in agreement. “The decision to extend the closure of the Esk Valley line was a joint decision reached with our colleagues at Network Rail. We chose to extend the blockade, as opposed to stopping work all together, in order to reduce the overall disruption to local communities in the Esk Valley.

“Although the work did overrun by five days, we managed to reduce impact as well as cost, by ensuring further blockades did not happen, especially during weekends, which are vital to Whitby’s busy tourism season. With both man and machine already onsite, it was a more cost effective approach for the industry on a whole, to remain there and finish the work which had been started.”

Looking forward

But what of the challenges – the birds, the weather, the cranes and the structures themselves? A thorough “lessons learnt” exercise was carried out the Monday after work completed to make sure it was fresh in the minds of all those involved.

Nesting birds were naturally top of the list. Thanks to the dipper, not only will future surveys be suitably timed to take account of bird nesting seasons, but wherever possible mitigation will be put in ahead of work starting to prevent the problem.

The ORR intervention was also discussed, along with the fact that the British weather will always remain a challenge. When working over water, worst case scenarios will be taken into account at planning stages.

As for combining works (four bridges, one job), it was decided that, for future projects, different scenarios will need to be tested through a schedule risk assessment process which challenges the robustness of the programme and the likelihood of success. Fallback plans should be in place to enable the right decisions to be made by project teams.

So that’s it. Four new bridges in the Esk valley. Darryl White Network Rail Scheme Project Manager just hopes that, on his next job, the opposing team of the gods, Mother Nature and the gremlins all stay at home!

Many thanks to Darryl White and the Network Rail and BAM Nuttall project teams for their courtesy and assistance in arranging a site visit and helping with this article.


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