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Improving Glasgow Subway’s tunnels

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At over 120 years old, Glasgow’s ‘Clockwork Orange’ Subway tunnel system is the third oldest underground urban railway still in operation throughout the world. Originally powered by a ‘clutch and cable system and driven by steam-powered plant between West Street and Shields Road stations, the whole system was first updated to electric power in 1933 and then the line was electrified in 1935. With rolling stock converted to electric traction, journey times were reduced and the comfort of passengers enhanced.

In comparison with other underground networks, Glasgow’s underground has a small tunnel bore – only 3.4 metres in diameter in most locations. Because of this, the scale of the track gauge is equally small at only 1,220mm (four feet).

There are also significant gradients as a legacy of the cable hauled system is that the stations are on a hump to aid deceleration and acceleration. Four types of tunnel lining construction have been used: Brick/Concrete Horseshoe, Cast Iron, Brick/Concrete Circular, and Brick Circular. Much of the tunnel’s lining is located underneath the water table and housed within a variety of different ground conditions – including clay, silt and rock.

Need for improvement

With passenger numbers swelling to over 13 million a year, a schedule of works was outlined in 2015 to mitigate any impact from the varied surrounding geological conditions.

As part of a £19.5 million tunnel lining improvement project, Strathclyde Partnership for Transport (SPT) approached specialist civil engineer Freyssinet to survey the tunnels and conduct a series of works to futureproof the service as the city’s principal method of transport.

The project called for upgrading the tunnel lining by grout void filling and lining repairs on a scale not previously seen on the network.

One of the key factors of managing the network is the need to control water, and there is plenty of that beneath the streets of Glasgow!

Ingress of water can affect signalling equipment, damage brickwork and corrode steel if it is not managed. Water ingress has many likely sources, but remains most common from burst water mains or underground water courses.

As a result, Freyssinet not only had to control water, it also had to ensure that SPT could continue to use the network for normal service operations. This meant that all enhancement and remedial works would be carried out at night when the network was closed.

Given its expertise in specialist grouting solutions, and experience as a legacy supplier to previous SPT grouting projects, Freyssinet and SPT turned to Tarmac’s Pozament team to supply the materials – Pozament SPA4 grout along with amended SPP2X grout for flowing water. These two products truly excel in these demanding conditions, providing the solution both Freyssinet and SPT were looking for.

Pozament was initially commissioned to supply 2,600 tonnes of specialist set accelerated tunnelling grout SPA4 from January 2016 to March 2017, delivering between one and two loads a week. The grout was to be installed during the night closures, between the hours of 00:00 and 04:00 each day, so as to allow the grout to cure ahead of the 06:00 line re-opening and to avoid disruption to the travelling public.

Change of plan

SPT’s original intention had been to upgrade the Subway without any closures. However, this was not possible for the renewal of the subway access ramps to the depot and its turnout chambers. Hence the entire underground network was shut down in July 2016 which provided an opportunity for 24/7 access
to the line. As a result, Freyssinet approached Pozament to supply 12 months’ worth of material in the 31- day window.

Whilst supplying the 1,000 tonnes of grout required for July proved straightforward, there were several logistical issues to overcome. There are no storage facilities available within the underground network, so all equipment and materials have to be loaded in and out of the network at the start and end of every shift.

From January to June 2016, to accommodate the limited working conditions, sacks of product were manually loaded on to small pallets and hoisted down the station’s fire escape staircase. However, the increased product supply for July would require much more space and man-power than was available.

Senior Freyssinet project manager Christophe Zapirain and his team overcame this hurdle by commissioning the design, manufacture and installation of a bespoke conveyor system fixed to the soffit of the station’s emergency staircase. The conveyor loading frame is fixed to a trackway which takes the load contained within a lifting stillage, allowing operatives to guide the load both in and out of the station platform area. This not only increased productivity but also reduced unnecessary manual handing.

Additionally, the design and manufacture of bespoke access ladders off station platforms to track level has provided safe access and ingress for operatives.

The Pozament team came up with a packaging solution and redesigned its pallet size to enable whole pallets to be hoisted down the fire escape staircases without prior unloading. This led to significantly faster installation times, keeping the project on track and allowing workers to cope with the extra volumes of material going through the station.

Freyssinet also commissioned a bespoke track-mounted heavy-duty working platform for use within tunnel sections. This was specially designed and fabricated to enable remote drilling, another innovation developed by the team. Using the drilling rig also avoided a significant issue on construction sites, that of hand-arm vibration.

With Freyssinet massively up- scaling its workforce to 30 grouting teams, Pozament supplied on-the- job training to ensure all workers were fully familiar with the product and its application requirements. As such, all planned work was able to be completed on time by the end of July, at no inconvenience to SPT.

Despite the significant unforeseen scheduling changes, Pozament successfully met the high volume product requirements and helped ensure there was a quick turnaround, fully utilising the rare opportunity that the month-long closure provided.

Christophe Zapirain commented: “The Pozament team, throughout the project, has been very proactive to assist our teams on site and meet our supplying requirements. The tunnel closure was challenging in all aspects and the Pozament team played a key role in delivering the significant amount of grout materials in a very short time window.”

The project is now nearing completion, with the final stages being undertaken to rehabilitate the tunnel lining.

Thanks to John Kennils of Freyssinet and Alex Wright of Tarmac Pozament for their assistance in preparing this article.


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