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The final countdown

July 28th 2010

Reopen our disused railways - for many years this has been the cry of enthusiasts and nostalgics. Mainstream thinking has caught up recently as it is realised that rail can offer a sustainable alternative to congested roads. One of the first steps taken by the devolved Scottish administration was to take a hard look at transport and authorise the reopening of a number of key rail links. The first passenger train for over 50 years is due to run between Airdrie and Bathgate before the end of this year but the project neatly illustrates the difficulties and realities of relaying old routes.

Routewise

The Airdrie to Bathgate project featured in last month's magazine with an insight into the track and electrification works. This month it is the turn of the structures. At the risk of boring those who read the route description last time and resisting the temptation to ‘copy and paste', a brief summary follows for structures engineers who skipped a piece apparently about OLE and turned to the next article about a rotten bridge.

With Airdrie at one end and Bathgate at the other, the project naturally lends itself to a three character abbreviation. The project team clearly saw this coming so chose to use a fancy arrow instead which isn't even in Wingdings, thus AÛB.

The station before Bathgate is Armadale which in turn is preceded by Blackridge. Therefore whilst you need to head east to get from Airdrie to Bathgate you can also do a different A to B heading west. The next stations beyond Blackridge are Caldercruix and Drumgelloch which means that you can take in D and C en route from A to B with an intermediate A-B rondo variation. At this point the map may prove of assistance.

Structure numbers

How many structures are involved? On the face of it knowing the answer would appear to be pretty crucial. However, the problem with this type of project is keeping track of the figures as every time you add them up they seem to change. Just beyond Airdrie Station is underbridge UB64 carrying Broomknoll Street. As the alignment curves into Bathgate it crosses golf club underbridge UB31. Do the subtraction: 64 less 31. Yes, there are 46 bridges involved!

The difference of course stems from the bridges added since the original Bathgate & Coatbridge Railway opened in 1863 such as OB62A and OB34A, and also the 13 new crossings required for the reopening. These include six new footbridges at the stations, other foot and cycle bridges to maintain existing rights of way and a number of new road links.

As you cut the numbers in different ways, it is clear why the figures jink around so much. The route started out with 33 existing bridges. One of these will be demolished and not replaced. The new structures will be added. As the project developed, footbridge 57A was deleted from requirements as the play area it was proposed to serve was found to have a rather antisocial recreational use. Thus that 46 total may really be 44 in the final count but could be 45 before the demolition occurs.

Non-operational civils works

Having got that cleared up, the design appraisal for the Parliamentary Bill talks of 103 bridges. Referring to Airdrie-Bathgate overlooks the fact that the project will create a new rail link between Glasgow and Edinburgh. On the west side, the route as far as Drumgelloch was already electrified as part of the Glasgow suburban network and double-tracked as far as Airdrie. However, to the east, doubling of the line from Bathgate to Newbridge Junction and electrification into Edinburgh were needed. Modification works to bridges on this section accounts for the other structures.

Thus extensive works were needed to 18 miles of operational railway in addition to the 15 miles of new link. Integration of the works and ultimately the new train service into the existing network was key, hence Network Rail was tasked in May 2005 with delivering the project.

The contract split reflected the need to start early on the operational sections with working time limited by the availability of possessions. Civils works here were carried out by Galliford Try, Jarvis and BAM Nuttall. Signalling and comms systemwide were done by Invensys. Track and OLE, as reported last month, were won by Balfour Beatty.

The civil engineering between Drumgelloch and Bathgate took the lovely title of ‘non-operational civils works' which probably confirms most people's suspicions of the abilities of civil engineers. In fact it refers not to the final product but to the state of the railway at the time of works. This was packaged separately to take advantage of the green-field nature of the site where the usual railway working restrictions did not apply, potentially opening the market to a wider field. Carillion was appointed to this £76 million contract.

Bridge specifics

Much of the scope of the bridge works was defined by the May 2006 Parliamentary Bill and its requirements. Key amongst these was the intent to electrify the line. Electric traction ticks a whole range of boxes - low emissions at point of use, reduced wear and tear on the infrastructure due to lighter vehicles, pleasant station environments and improved passenger comfort with a quiet ride.

However, electrification needs space for the wires. Extensive reconstruction was needed to provide W10 loading gauge with minimum 4.68m clearance from rail level or 4.78m for new structures. Of the 49 existing overbridges between Airdrie and Edinburgh Haymarket (another different number), 60% were too low so 22 were rebuilt with greater clearances and seven demolished. Of the 40% retained, 14 needed parapet modification works and only three needed no works at all, these on the section between Airdrie and Drumgelloch which had already had its single line electrified.

The overbridge rebuilding programme had a number of advantages - not least it guaranteed a 120-year design life with low maintenance. Parapets and approach barriers which comply with current H4a standards were built-in. Risks were much reduced compared to the uncertainties of structure refurbishments. However, economies of scale are little consolation when so many bridge reconstructions were needed to provide clearance, particularly when some of the removed structures were still in fair condition. It's no surprise that the structures budget was significant - around £15 million was estimated when the Bill was submitted.

In situ integral portals were used extensively to remove the need for bearings and expansion joints, taking advantage of the luxury of having time to cure the concrete. Other common designs for on-line reconstructions reused the existing abutments, casting new cill beams and often inserting U-troughs between the toes, with Macrete precast beams for the decks.

Work scope for the underbridges was assessed depending on their merits and condition. Even so, extensive reconstruction was needed - between Airdrie and Bathgate, six of 14 underbridges were redecked with a further two new decks beyond Bathgate. Lanarkshire Steel and Mabey Bridge provided a clutch of steel decks apiece. A further five underbridges were waterproofed to reduce future maintenance, excavating down to the crown for the arch structures.

So reusing the existing infrastructure provides the formation and alignment. But, particularly if the switch is made to electric traction, you may effectively need to start again on the majority of the structures. Another statistic - including all 33 existing underbridges and overbridges between Airdrie and Bathgate, 70% needed significant structural alterations with only ten avoiding major works.

The human factor

Even the trackbed is not guaranteed though. When the railway closed to freight in 1982, the advantages of the abandoned route were seen by cyclists as the solum was turned into National Cycle Route 75 - a similar fate has befallen many disused rail lines. Reopening the railway also meant catering for the existing users of the route by reinstating an alternative cycle route at a cost of £7 million.

Creation of modern infrastructure also needs to take into account maintenance requirements. A single cess route has been provided adjacent to the Up line throughout using modular TroTred units to provide a combined cable route and walkway. Slope works, gabions and retaining walls have been needed to increase the formation width. Earthworks were complicated by the poor ground conditions throughout the route, particularly the 20m depth of peat underlying the area around Hillend reservoir. At the underbridges a combination of redecking, cantilever arms and new external footbridges have been used to provide the continuous walkway.

Fast track

The project timescales bring a whole new meaning to the phrase high speed rail. From the time the Bill was submitted, the published in-service date has been December 2010 - and the project is still on course to achieve this. Short design and tender periods were the order of the day. The design and construction contracts were kept separate, enabling the design to be progressed by Scott Wilson whilst the Bill was under consideration.

Detailed designs were therefore available for many of the structures prior to letting the construction contracts, enabling the prices to be fixed. Inevitably external factors led to uncertainty for some bridges: OB35 at Armadale had adequate clearance but failed its assessment and was due to be replaced as part of developer-funded improvements to the road network. The property downturn put this on hold but regrettably did not change the project deadline - it was decided to strengthen the existing bridge instead as the unusually deep 750mm of fill allowed new I-beams to be installed within the available construction depth.

Protracted negotiations over a 48" gas main at OB43 led to a projected three-month delay. The proposed three-span bridge would have straightened a nasty kink in the A89 at Bedlormie Toll. In what is termed a mid-project efficiency, the design reverted to a single span redeck on the existing road alignment to improve the programme and save on costs. The girders - already fabricated by Mabey Bridge - ended up being modified to suit an alternative design for UB57 to avoid extensive temporary works in the river. To keep things moving Network Rail's framework with Carillion was used to procure the designs by Cass Hayward while the build was varied into the construction contract.

Collaborative working was needed to overcome delays due to the atrocious weather at the start of the year. Originally it was planned to hand over complete route sections to the trackwork contractor. The pain of delayed handover in some areas was eased by allowing early access elsewhere so that tasks such as OLE foundations could commence. There has been a desire from all involved to be associated with a successful project which has undoubtedly eased these interfaces. Shared project offices have also helped, with Network Rail, the designer and the contractors all based in Armadale.

Technical approvals are the bane of many a construction programme. In this case Network Rail gave themselves 14 days to sign off with comments on the first submission. An additional complication was that the bridges carrying public roads would revert to the local authorities so an additional page (and an eighth signature) was added to the Form A for highways authority approval. The road-based approvals such as approach barriers were split out from the structures approvals - a good decision given the lengthier timescales for the highway authority responses.

It's all relative

The Airdrie Bathgate Rail Link project has attracted much interest and observation. Albert Einstein obviously knew about the project when he commented, "Logic will get you from A to B. Imagination will take you everywhere." Fortunately engineers are a pretty logical lot, although a considerable amount of imaginative thinking has been applied in the process. According to American author E B White, "Everything in life is somewhere else, and you get there in a car." It is precisely to change this sort of attitude that Transport Scotland is investing £300 million in the rail link which is expected to open on 12th December 2010.

The final countdown

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