A legacy of the rapid early growth of Britain’s railway network is that the UK has one of the world’s most restrictive loading gauges. As a result, typically half of the cost of British electrification projects is the civil engineering work to adapt structures to provide clearance for wires and pantographs.
The £742 million Edinburgh Glasgow Improvement Project (EGIP) will electrify the Edinburgh to Glasgow main line that carries around 20,000 passengers each day and is Britain’s busiest inter-urban route (one that does not go to London). The line opened in 1842 and its electrification requires work at almost all of its original structures. Inevitably, the scale of this work brings disruption to both rail passengers and road users.
With clever construction techniques, the railway closures associated with bridge replacements can be limited to long weekends. However, increasing clearances in tunnels is a different matter as the logistics of such work may require a rail closure of a matter of weeks or longer.
For example, the tunnel at Farnworth, near Bolton, is closed for five months whilst the tunnel-boring machine increases its diameter (issue 127, May 2015).
As part of EGIP electrification, Winchburgh tunnel, just east of Linlithgow on the route out of Edinburgh Waverley, required track lowering up to 200 mm and the installation of slab track at a cost of £17 million. This is an essential element of the Edinburgh to Glasgow electrification, which will transform train services across Scotland’s central belt.
Unavoidable severe disruption
As a result, Scotland’s busiest line was blocked for 44 days between Linlithgow and Edinburgh where there was no straightforward diversionary route. This entailed severe disruption that was partly mitigated by starting the diversion on 13 June to take advantage of the holiday season and ensuring the line was open in time for the Edinburgh Festival.
During the tunnel closure, through passengers were encouraged to use other routes between Edinburgh and Glasgow on which there were some extra trains. Dunblane to Edinburgh trains continued to run via Linlithgow and the Fife lines after reversing at Dalmeny. As these trains did not provide sufficient capacity for commuters to Edinburgh at the eastern end of the line, replacement buses were provided between Linlithgow and Edinburgh – increasing the journey time from 22 minutes to over an hour. In the event, the buses ran empty as commuters turned to their cars.
Unfortunately, there was no way of avoiding this significant disruption. Critics pointed out that it would not have occurred had the Dalmeny chord in the original EGIP plan been provided (issue 104, June 2013). Yet, with two grade separated-junctions, this chord would have cost £175 million and could only have carried a small proportion of Edinburgh to Glasgow traffic as the Fife lines are heavily trafficked.
What was done before the Winchburgh blockade was to complete a signaling upgrade on the route between Edinburgh and Fife for which a £16 million contract had been awarded to Siemens in January. This included replacing 3-aspect with 4-aspect signals between Dalmeny and Edinburgh and the installation of six new signals on the Forth Bridge. As a result, diverted trains could reverse at Dalmeny without disruption to the train service.
Winchburgh tunnel lies at the eastern end of a five- kilometre long cutting. It is 338 metres long and was opened in 1842, having taken two years to complete. When digging the cuttings and tunnel, the contractor, Gibb and Sons, removed 200,000 tons more rock than expected and consequently made a loss.
The tunnel was cut through dolerite rock, mudstone and shale. In the middle on the nineteenth century, these oil shale deposits once made West Lothian one of the world’s biggest oil producers. This shale was also a factor in an unfortunate accident during tunnel construction in 1839 when a man was severely burnt by firedamp.
The cutting is crossed by two streams, west of the tunnel. A twin four-foot diameter cast-iron inverted syphon was provided to carry Myers Burn under the railway. Swine Burn crosses the cutting on an aqueduct that had to be re-decked as part of the EGIP electrification works. Downstream of the aqueduct is a pumping station, which drains the cutting west of the tunnel. This is an area with significant drainage issues, some of which are addressed by the tunnel works.
The tunnel has a pointed roof profile and had a narrow six foot (1571 mm) which the tunnel works marginally increased to 1605 mm. Lowering the track by up to 200 mm, together with the use of a Furrer+Frey Rigid Overhead Conductor Rail System (ROCS), was just sufficient to provide the required electrification clearance. To ensure this clearance is maintained the track has to be fixed in position requiring the installation of slab track. This will significantly reduce track maintenance in the tunnel and increase speed through the tunnel from 80 to 90 mph.
The Austrian Solution
The principal contractor Morgan Sindall chose the ÖBB- PORR Austrian slab track system for the Winchburgh project. This is its first use on the UK rail network although it had been trialled on the Old Dalby test track in Asfordby tunnel (Rail Engineer June 2014). The system was jointly developed by Austrian Railways (ÖBB) and Allgemeine Baugesellschaft – A. Porr. It was first used in 1992 and since 1995 has been Austria’s standard slab track system. Since 2001, it has also been widely used in Germany where the Erfurt to Leipzig high speed line used 180 km of the slab track. There is now around 580 km of the ÖBB-PORR Austrian slab track in use.
The principal element of the system is a 160 mm thick concrete base plate that has eight pairs of track fastenings. There are three different plates for straight track and different curves. The base plates are secured on a suitable flat base by self-compacting concrete (SCC) that is poured through 640 mm square tapered openings in the base plate after it has been accurately positioned. The SCC reinforcement and 80 mm thick support blocks are first placed on the flat base, which is sufficiently flexible to be positioned using the five jacking screws in the base plate.
The base plate incorporates an elastic rubber coating which absorbs vibration. This coating also serves as a barrier between the base plate and the SCC. This enables the SCC to be easily broken out and the base plate removed in the event of derailment damage. This can be done in a matter of hours once rails are removed.
44-day track transformation
The main contractor for the Winchburgh tunnel works was Morgan Sindall who secured a £113 million position on the £250 million alliancing contracts for EGIP infrastructure works that Network Rail awarded in November. The work started with the establishment of a large compound at the eastern end of the tunnel, which took five weeks. After the compound was established, two weeks were spent installing new track drainage either side of the tunnel during disruptive possessions. Then it was time to install the slab track during the 44-day blockade.
Other tunnel work during the blockade included a new drainage system, installed at invert level next to the base slabs, and the installation of fixings for the conductor rail system that is to be fitted later as part of the electrification works. About 10 square metres of brickwork needed repairs, but otherwise the tunnel lining was generally in good condition.
Although the project required no work on signals, tunnel wall mounted cable supports were provided to lift cables from the trackbed.
Tunnel logistics required that one track be available at all times for the supply and removal of the large amount of material. Thus, it was not possible to work simultaneously on both lines. The plant movements for handling this volume of material, adjacent to work undertaken in such a confined area, required a detailed work plan to prevent conflicts and delays.
A robust site-specific safety regime was implemented which included special rules for plant movements, health screening for Weil’s disease and extractor fans. These were provided by Factair who also undertook air quality monitoring.
The first track to be lifted was the Up line. The track, ballast and formation was typically 1.2 metres deep and removal of this material revealed the tunnel invert for probably the first time since the tunnel was built. The invert itself had then to be treated to remove loose mudstone and high dolerite rock outcrops. Steel dowels were then fixed into the base rock to secure the concrete base slabs.
On the fifth day of the blockade, the first base slab was poured. It took five more days to pour all the base slabs which varied in depth from the minimum allowable 150 mm to 600 mm where a large amount of mudstone had been removed.
By day nine, the first base plates had been positioned outside the tunnel mouth. To provide a transition to ballasted track there is 70 metres of slab track outside the tunnel. The usually problematic ballast to slab interface was overcome by installing the Rhomberg Sersa V-TRAS Module, also first trialled by Network Rail on the Old Dalby test track in Asfordby Tunnel (Rail Engineer June 2014) which offers a long term maintenance free transition solution, giving each line a total of 470 metres of slab track.
Drainage and permanent way works were undertaken by sub-alliance partner Babcock which also cast the base slabs and procured the services of Rhomberg Sersa, the licensed installers of the ÖBB-PORR Austrian slab track. It took two days to accurately position all the slabs on one line. When there were sufficient slabs in place, 110-metre length rails were fitted on them to ensure accurate positioning.
Watertight formwork was needed as the self-consolidating concrete (SCC) is very fluid. After the SCC pour, it took 24 hours before the track could carry traffic. The slab track was then complete and the process was ready to be repeated for the down line. A press release on 4 July, and visit from the Scottish Transport Minister, confirmed that the work was on target at this halfway point.
The Winchburgh improvements almost eliminate maintenance in the tunnel, increase the speed through it and significantly reduce the flood risk. The work required the removal of 2,000 cubic metres of spoil, casting of 1,200 cubic metres of concrete, removal of 200 tonnes of rock, reworking 825 metres of drainage and the installation of 188 five – metre slab base plates. All this work required a total of 80,000 man-hours of work.
More to come
Doing all this work in 44 days is a worthy achievement. However, it was not likely to impress most commuters affected by the six-week Winchburgh blockade work who were more concerned with their journey to work. Communicating why this work was necessary and what it entailed was a significant challenge. It involved a big campaign by both Network Rail and ScotRail that included use of social media to engage with those affected and give good detailed information about the work.
A similar campaign will be required next year when the line’s commuters face another blockade when the tunnel into Queen Street Station will be closed for 20 weeks as its 40-year-old slab track is deteriorating. The ÖBB-PORR Austrian slab track system is also to be installed in this 1.9km long tunnel.
While this is not strictly part of the electrification works, as the tunnel already has the required clearances, it forms a precursor to the extensive remodelling of Queen Street high-level station. This cramped terminus is to be extended with longer platforms that are an essential part of the electrification scheme. Phil Verster, managing director of the ScotRail/Network Rail alliance, considers that the new station will be stunning and “on a par with St Pancras or King’s Cross”.
Electric trains will start running between Edinburgh and Glasgow in December 2016. The forthcoming electrification is evident from the masts starting to appear along the line along with extended platforms. Most of this work is being done at night with no disruption to passengers.
Unfortunately, the route’s tunnels are another matter, so its commuters face unfortunate disruption before they see their electric trains. Then they will have a more resilient network with the faster, longer trains needed to accommodate growing passenger numbers. So the few weeks’ disruption at Winchburgh was an unavoidable part of transforming central Scotland’s train services.