Upgrading the world’s third oldest subway has posed some new challenges.
Trains leave and enter Glasgow Subway’s 10.5km underground loop via long, turning ramps, which connects to a depot and maitenance shed at surface level.
The ramps and turnouts for the depot were life expired, with the last update taking place in the 1970s. More specifically, the long shopping list of required works included: geometry re-design (horizontal and vertical alignment), a new trackbed system, drainage, third rail, signalling, as well as track components (point motors, switches and crossings).
Nineteen companies showed official interest in the tender for the upgrade work. Three bids were received in November 2014, and Colas Rail won the £5M design and build contract for the work.
Over a four week possession 2,400t concrete was poured and 2,500m rail laid, using 1,487 rail blocks each weighing 92kg and 1,030m of conductor rail. Subway services were suspended on 2 July, 2016, and reopened for service from 10 August.
Complicating the job for Colas was the fact that Glasgow’s subway trains run on a bespoke rail system, dating back long before track gauge standardisation. Victorian-era politicians were positively proud of how unique and ground-breaking their subways were, so there was little standardisation with other metro systems.
The Glasgow Metro runs on an unusual 1,220mm gauge and 39E1 rail sections, in tiny 3.4m diameter tunnels. Standard plant just does not fit, and so workarounds and modifications were needed.
01 Ramp install prior to concrete pour
Logistically, workers and plant could only access the tight spaces via the turnout ramps, and so the operation was sequenced to work backwards out of the tunnels and up to surface level. Concreters had to pump large distances using a fibre reinforced C30/36 mix.
First to go was the concrete above the unreinforced concrete structural floor slab that varied in depth between 30mm to 75mm below the old timber bearers. Associated track bed concrete, sleepers and rails and conductor rail equipment were also removed.
The track bed was replaced by Sonneville low vibration track blocks – concrete blocks in rubber boots – cast into a fibre reinforced concrete slab utilising a top down method. This involved suspending rails and blocks from jigs, set up to the design levels before the in-situ concrete was cast around them.
02 Ramp concrete pour
The switches and crossings units were bespoke manufactured units with additional heat treated specifications to prolong their lives. Existing 2m point machines were replaced with Contec CSV24 4ft mounted units.
The existing conductor rail components and track were entirely replaced with new modern equivalent components utilising a new standard composite conductor and brackets. Signalling changes were limited to minor alterations to track circuits and bonding arrangements.
Such was the rarity of a month-long possession on the line, other sectors within Strathclyde Partnership for Transport (SPT) accelerated works that would otherwise have been done within short nightly possessions. These included checkrail replacement works, station refurbishments and tunnel lining improvements.
Importance was placed on getting enough time to remove, replace and cure the concrete, up to trafficable strength within the four week window.
At a grand old age of 120 years it might surprise some to learn that this is only the third time Glasgow Subway has undergone major surgery, after being electrified in the 1930s (originally it was a cable-hauled system), and a modernisation in the 1970s.
In the 1970s all 15 stations were upgraded and the system went from ballasted track with timber sleepers to a concrete track bed with cast in rail blocks.
Also carved out in the 1970s was the new turnout ramp section, requiring earthworks, concreting and track laying, which took more than three years. This expansive and high-walled passage meant that rolling stock no longer had to be dropped into the loop via a crane at a depot at Broomloan.
01 Ramp install prior to concrete pour
But the quality of the 1970s concrete later posed problems, as it began to crack. Chiefly, the surface concrete on turnout ramps degraded. As a patch-up job, owner and operator SPT undertook regular maintenance to inject resin into the concrete cracks. But successive winters brought on more deterioration due to water ingress, which would then freeze and thaw, further shifting the concrete.
Water ingress is a perennial issue for the subway which runs under the River Clyde. Much of SPT’s work has been to reduce, rather than eliminate, water risk. This alleviation work involves improving the structural lining, removing voids, diverting water away from the track system and improving pumping systems. A Knowledge Transfer Partnership with SPT and Glasgow Caledonian University has led to an award-winning project that aims to harvest the water and use its energy as a sustainable heat source in the stations.
120 years’ young
To fully understand the loop model of Glasgow Subway you have to understand the city’s history.
When the Subway first opened, Glasgow was the Second City in the Empire and its population growth was spectacular.
It was the largest city in the world and also the wealthiest thanks to its trading connections.
The 10.5km loop was built around the River Clyde and designed to move vast numbers of people about the city quickly and easily so they could get to work in the shipyards of Glasgow, mostly on the south bank of the river.
Using the Subway was the quickest way to get around and in 1918 it carried almost 21M people passengers. By 1922 that dropped to almost 8M as people preferred the expanding tram network.
Then during the Second World War, patronage rose again significantly as shipyard activity increased on the Clyde.
This continued after the war and in 1949, patronage reached an all-time peak of 37M.
Today about 13M passengers use the system per year, or about 40,000 a day
But rather than shipbuilders’ patronage, it is now more likely to be university students or city workers.
Potential expansions have been mooted in decades past, but the £bn’s required have never been on the table.
Instead, retrofitting and digitisation is the way forward. New trains, signalling and equipment valued at £200M are expected in the next five years, with the contract awarded to the Stadler Bussnang/Ansaldo STS consortium.
There will be 17 new train sets in all, the same length and size as existing rolling stock but instead in a four-car orientation, as opposed to current three-car. Open gangways will maximise space and allow for wheelchair access.
Upgraded control systems and a control centre are also intended to improve availability and reliability. The unattended CBCT Communications Based Train Control system can, due to its real time nature, facilitate smaller headways and more efficient deployment of the same number of trains.
“Unattended train operations will eventually come into play but not until all trains are in service, the signalling and operational control centre and the new platform screen doors are in place so sometime after 2021,” says SPT senior project engineer Eric Thomson.
“There’s nothing for passengers to worry about, the trains we have at the moment are already automatic train operation so this isn’t such a huge leap.
“Unattended train operations are standard in many other European countries and people are used to that and are comfortable with it.”