On New Year’s Day in 1842, the citizens of Glasgow were able to walk through the newly constructed 1159-yard tunnel into Queen Street station, at their end of the Edinburgh and Glasgow Railway. The tunnel had been whitewashed and gas-lit for this event, which raised funds for those injured building the railway. The railway opened on 21 February that year, with four trains a day between the two cities taking 21⁄2 hours.

The railway company had originally intended to approach Glasgow by a bridge over the Monklands canal and build a station just north of the present station. However, the canal company opposed this, so a tunnel under the canal with a 1 in 44 gradient was required. This was too steep for locomotives of the day so, up until 1908, trains were hauled up this incline by cable and descending trains had a special brake wagon.

This steep tunnel continues to present operational and maintenance problems, although the canal is long gone with most now buried under the M8 motorway. Yet the canal company’s objection gave Glasgow its Queen Street station, which was closer to the city centre than originally planned.

The original station soon proved woefully inadequate for its increasing traffic and so was rebuilt between 1878 and 1880. The tunnel, whose original southern portal was just south of Cathedral Street, was shortened by 153 yards to create a new station throat and platform extensions. The wrought-iron arched roof was built at this time. As part of an East-West line under the city, the Low Level station was excavated underneath the original station and opened in 1886.

Out with the 70s

In the 1970s, concrete slab track, then a new innovation, was installed to reduce track maintenance in the heavily used tunnel. As this slab track is now at the end of its design life, it has been subject to much remedial work, including the use of ‘hedgehog’ sleepers with protruding reinforcement to key into the infill concrete. In 2011, Pandrol SFC baseplates were installed under the tunnels’ track to provide horizontal adjustment to compensate for the deterioration.

With station usage set to grow from its current 20 to 28 million passengers by 2030, Queen Street station has to be rebuilt. Standing in the way were some other 1970s developments, Consort House and the station’s adjacent hotel extension, both of which obscure the station frontage. When the station rebuild starts in 2017, these buildings will be demolished to reveal the arched roof and increase the station’s footprint so the new station can have increased concourse space, improved accessibility, remodelled passenger facilities and longer platforms.

Lengthening the platforms is being undertaken in two stages. The first is re-modelling the station throat, along with associated platform alterations. The second stage is the major station rebuild which includes further platform extensions. This will enable new electric trains (issue 139, May 2016) to operate in seven-car formations from December 2017 and as eight- cars from December 2018.

With the need to both replace 1.8 kilometres of tunnel slab track and undertake station throat works, a lengthy closure of Scotland’s third busiest station was inevitable. So, on 20 March, Queen Street High Level station was closed for twenty weeks. During this time a comprehensive plan ensured passengers could get to Glasgow, albeit with extended journey times. Trains were diverted to the Low Level station or the city’s Central station, additional use was made of the line via Airdrie and Bathgate and extra local buses were provided for local stations.

The main Edinburgh to Glasgow trains were diverted over a new junction at Anniesland to the west of the city, built at a cost of £20 million specifically for this purpose (issue 136, February 2016). This involved a 20 kilometre circular diversion through the North Clyde lines to the Low Level station.

£60 million blockade

This 141-day closure follows a 44-day blockade last year to install slab track in the 338-metre long Winchburgh tunnel (issue 130, August 2015). This was the first UK use of the STA (Slab Track Austria) slab track system, which is being installed in the 918-metre long Queen Street High Level tunnel as part of this blockade. This, and the associated station works, will require around half a million man-hours work and cost £60 million, with an approximately equal split between the tunnel and station work.

It took two years to plan the complex interaction between all the work packages for which the main constraint was the need to keep one line through the tunnel operational at all times to deliver the work. Network Rail considers this to be the largest piece of engineering work on the Edinburgh- Glasgow railway since it was built.

Principal contractor for this work is Morgan Sindall, which was awarded an alliance contract in 2014 for the core EGIP physical works. This is a risk- share agreement – intended to create a collaborative environment.

Morgan Sindall has engaged CPR for platform extension work, Story Contracting for the removal of the existing slab and construction of the base slab, Siemens for signalling and Babcock for the trackwork which, in turn, procured the services of Rhomberg Sersa who are the licensed installers of the STA slab track system (manufactured by Porr AG). Rhomberg Sersa would also install the Sonneville LVT slab system for the S+C within the tunnel. Another EGIP alliance contractor, Costain, installed the station’s OLE and a Furrer+Frey conductor bar in the tunnel.

Work outside the tunnel

Track renewals work undertaken by Amey Sersa north of the tunnel started as soon as the blockade possession had been taken. This involved the renewal of three kilometres of track and five point ends, and the refurbishment of four more. This restricted movements into the tunnel, so slab track work could not start in earnest until this phase was complete.

Complex S&C arrangement from tunnel portal

Other work north of the tunnel was the demolition for electrification clearance of Gourlay Street and Fountainwell Place bridges at the end of May, during a three-day window when train movements were not required through the tunnel.

Also starting as soon as the blockade was taken was a 13-week programme to reconfigure the station throat to accommodate seven-car class 385 units. This involved 2,000 cubic metres of platform demolition and the construction of 642 metres of platform walls. 615 metres of new track was laid in the station as well as seven new switch and crossing units on timber sleepers, which were first constructed off-site to check components and methodology. A further four S&C units (slab track S+C) were replaced in the tunnel and a total of 455 metres of new drainage was installed.

Other work in the station included a new housing for the upgraded signalling, a new signal gantry and the provision of nineteen OLE structures with associated wiring. New standards were provided for lighting and the station PA system, which had previously hung from the station roof but could not remain there after electrification.

The project team took advantage of the blockage to excavate platform wells beyond the current buffer stops. As there is no space to extend platforms until the station is rebuilt, these were filled with polystyrene blocks and resurfaced for easy excavation during the station rebuild.

Breaking up the slab

Unlike Winchburgh, the Queen Street work required the removal of the previous slab track. With the unprecedented nature of this work, a trial breakout was undertaken in December to confirm the proposed methodology. This removed 20 metres of the tunnel slab track, which was then temporarily replaced with ballasted track.

Other advanced works included the removal of redundant tunnel cables and, at the top of the tunnel, the provision of a cut-off drain into a sewer to minimise water flow into the tunnel.

Once the blockade started, tunnel, lighting, ventilation and communication systems were installed and a coring machine was used to prepare the slab track for its removal prior to completion of the track renewals work north of the tunnel.

Story Contracting project manager Eddie Esdale is responsible for the removal of the old slab track, constructing a concrete base layer that would eventually be used to construct the new slab track on and installing a new drainage system between the Up and Down base slabs.

To minimise vibration, the old slab track was first cut up by horizontal and transverse saw cuts and then broken up using remote hydraulic breakers. Specialist concrete cutting contractor Corecut was engaged for this work, which produced 10,000 tonnes of concrete lumps which were removed from the tunnel on trains that each took 400 tonnes. Once the base sandstone rock had been exposed, it was found to be uneven and had to be trimmed between 50 and 300 mm to lower track level by 30 mm.

This work was completed in two seven-week phases, first the Up line then the Down line. Eddie regarded the logistics of the blockage to be the biggest challenge with a train going through the tunnel every day for the station work and work north of the tunnel sometimes blocking access. Typically, his work required a materials removal or supply train each day, with three on-track machines and three off-track machines working in the tunnels in addition to various hand trolleys.

Eddie and his team had to mitigate the risks of working in a tunnel with such a severe gradient, for which a number of precautions were taken. These included the use of low rail on-track plant for better traction and braking and a specially devised clamping system for hand trollies.

Supply by shaft

The concrete for the STA system base slabs was supplied through the two original tunnel construction shafts. These are around eight metres square and capped with decks on 300 mm full width cast beams.

To get concrete through these capped shafts, surveys and temporary design calculations were undertaken to determine where they could be penetrated. A 75 mm pilot hole was then drilled from which a 200 mm hole was created for the 120 mm pipe through which concrete was poured into a trailer wagon attached to a road-rail excavator and taken to the cast slab framework awaiting its concrete. This shaft hole was also used to supply water and compressed air to the tunnel.

Casting the base layer required 2,500 cubic metres of concrete. On the Up line, the first base layer was cast on 21 April and the last one on 19 May. 3,245 steel dowels, drilled 2.2 metres into the base rock, were required to anchor these slabs.

The Austrian system

Rhomberg Sersa first trialled the STA slab track system on the Old Dalby test track in Ashfordby tunnel (issue 116, June 2014). It is Austria’s standard slab track system and is widely used in Germany having recently been used on the German VDE High Speed Rail Project.

The principal element is a 5.2-metre-long, 160mm thick concrete baseplate with eight pairs of track fastenings. These are secured on the concrete slab by self-compacting concrete (SCC) that is poured through 640mm square tapered openings in the baseplate after it has been accurately positioned. The SCC reinforcement and 80mm thick support blocks are first placed on the flat base, which is sufficiently flexible to be accurately positioned using the five jacking screws in the baseplate.

The baseplate incorporates an elastic rubber coating to absorb vibration and which also serves as a barrier between the baseplate and the SCC. In the event of derailment damage, this enables the base plate to be replaced in a matter of hours once rails are removed by breaking out the SCC.

On 3 June, Network Rail announced that the blockade had reached its half- way point and, with the Up line finished, was on schedule to re-open the line on the 8 August. By 11 July, all the STA units were in place and the main work remaining in the tunnel was Costain’s installation of the Furrer+Frey overhead line conductor bar.

The PM’s tour

On 14 July, Rail Engineer was given a tour of the blockade works by the project managers from Network Rail and Morgan Sindall, Gary Murphy and Neal McKenzie. At this time, the slab track was complete, tunnel conductor bar brackets were being installed, platforms were being prepared for surfacing and most station OLE masts and brackets had been erected.

Gary also stressed the point about the logistics involved in keeping one line open and that the blockade always had to be ready to accept ballast trains through the tunnel. He advised that, while almost all heavy materials were delivered and removed by train, some were also supplied through the site compound at Queen Street station, where lorry weight was limited due to the bridge over the Low Level line. A part-road closure had been taken on the Cathedral Street bridge over the station to supply materials, including pumped concrete and the bricks and copes for platform re-construction.

Neal mentioned that the three parts of a new signal gantry had also been delivered from this bridge. After its assembly on the station’s tracks, a 250-tonne Kirow crane had been brought through the tunnel to lift the completed gantry into place. This crane was booked months before the blockage and is an example of the detailed planning that had taken two years.

Preparing tunnel floor for concrete base next to installed track

Neal commented that the only time that work didn’t go to plan was when unknown services were found in the platforms. One item found during the excavations at the station throat was a pulley wheel from the original cable haulage system, a reminder of the tunnel’s heritage.

As with most projects, signalling work is generally the last to be completed. At the end of the blockade is a ten-day wheels-free commissioning period. This reflects the signalling works undertaken which include the replacement of track circuits from the buffers to the north portal by Thales AzLM K axle counters. All signals within this area were replaced with Dorman signals with LED heads used in the tunnel.

The new points in the throat have SPX In-Bearer Clamplocks, while those in the tunnel are operated by HW point machines. To accommodate new despatch arrangements for the class 385 units, new equipment is being fitted to enable platform staff to operate indicators for closed door (CD), right away (RA) and train ready to start (TRTS).

Eventual transformation

Regular passengers will be glad to see normal services from Queen Street High Level resume on 8 August, although some may wonder why the station has been closed for twenty weeks.

A huge amount of work was done during the blockade, but this may not be evident to the average commuter, especially if they don’t follow the informative @NetworkRailGQS Twitter account.

It may be some time before such passengers notice a difference. They should see the first new Class 385 electric units in August next year, which will operate a full Edinburgh to Glasgow seven-car formation service in December 2017 to provide 27 per cent more seats than the current six-car Class 170 diesel units.

By then, the reconstruction of Queen Street station will be well advanced. Unlike the current blockade, this should not disrupt train services as the required track and platform alterations are minimal and have been partially completed by this blockade.

By December 2018, a full eight-car service will be introduced, offering 45 per cent more seats than the present service. Journey time between Scotland’s main cities will then be reduced to 42 minutes. A few months later, the new Queen Street station will receive its final touches. By then the transformation will be evident to all.