Installation of the last 1.5m long ring of segmental lining for the Costain/Vinci JV completed excavation on the 4.7m diameter 3.1mile long Shieldhall sewer tunnel in Glasgow. The focus now for the largest investment in the Greater Glasgow waste water infrastructure in more than a century is to connect the tunnel to the existing waste water network before it becomes operational next year.

The tunnel is a key part of the £250 million, five-year programme by Scottish Water to improve river water quality and the natural environment. The new sewer runs from Craigton to Queen’s Park via Bellahouston and Pollok parks. The route was chosen to maximise the use of parkland and minimise urban disruption during construction.

With an additional storm water storage capacity of 90,000m³, the project will alleviate pressure on the existing network, reduce the risk of flooding in parts of the Mount Florida, Toryglen and Giffnock areas and improve screening of overflows into the River Clyde.

The 180m long, 4.7m EPBM, supplied to the project by Herrenknecht, excavated at a speed of 2cm/min, through challenging ground. The cutterhead, dressed with 25 cutters, succeeded in geological conditions that included boulders, clay, hard sandstone, glacial tills and old coal workings.

During construction the tunnel passed beneath the Glasgow Paisley Canal railway line and the M77 motorway.

Shieldhall facts and figures

• More than 3,200 1.5m long concrete rings were installed
• Each ring comprised six segments weighing 2.5 tonne each
• More than 500,000 tonne of earth, stone, clay and other aggregates was excavated
• Construction took more than 1.5 million working hours
• More than 90% of the excavated material has been or will be recycled

It is a daily work commute with a difference for a team of engineers and professionals in the crew working on the Shieldhall tunnel project for Scottish Water in Glasgow.

“Getting to my place of work is certainly quite different to what most people do every morning above ground,” said Tom Rushe, one of the crew, “but I would never want a conventional office job. Building tunnels is cool and I really would not swap it for anything.”

Rushe and his colleagues are part of a team of engineers working with the 5.5m diameter Herrenknecht slurry TBM to complete the 5km long sewer tunnel at up to 32m deep and at progress rates of up to 30m a day. Progress has been steady and crews recently completed the first 1.6km of the tunnel.

Each day, the working shift starts at 7am and runs to 7pm when the second crew arrive for the 12hr nightshift. The workers, who work for the project contractor Costain/Vinci JV, follow this pattern five days a week, as the machine tunnel advances on a 24hr, night-and-day operating schedule.

Arriving at the Craigton industrial estate working site, the men receive a briefing from the shift engineer that includes an overview of the type of ground they will be working in, before heading to the 20m deep access shaft.

With their own tally number in hand, they descend the four-flight metal stairway. Covered by a sound-proofing roof to minimise noise inconvenience to local residents, the shaft accesses the tunnel staging area where all materials and supplies load onto service trains pulled by an electrically-powered locomotive for travelling into the heading, and all excavated material is extracted. By the end of the project, about 250,000 tonne of excavated material will have been lifted out of the access shaft and more than 18,000 precast concrete segments, weighing 2.5 tonne each, will have been installed.

At the bottom of the shaft, the crews also load into the manrider for their commute to the TBM. As they being work, they pass the small, encased wooden carving of Saint Barbara, the patron saint of tunnellers, which is mounted on the shaft wall to keep silent watch over them in accordance with tunnelling tradition.

The TBM, named Daisy the Driller by a local schoolboy, is an impressive and complex piece of kit. It is 180m long from its cutterhead to the end of its associated equipment training backup. Working in the narrow underground tunnel boring environment is challenging but there is a mess room, kitchen facilities and toilets for the convenience of the crews who spend their days and nights down in their special work place. Workers must be skilled and well trained to work in the confined spaces of the tunnel.

At any one time, there is usually a team of about eight crew working on the TBM, operating it and the support equipment it uses to excavate material and build the six concrete segments in each 1.5m long ring as the heading advances. Another 20 support staff work behind the machine extending pipework and cables for water supplies and power, ducting to convey fresh air into the heading, and extend the pipework circuit that carries the excavated material in the slurry suspension back to a slurry treatment plant on the surface and returns cleaned slurry back to the TBMs excavation chamber.

The Mixshield cutterhead is dressed with 25 disc cutters that penetrate the soil ahead at about 2mm per minute. With the ring building operation behind, the crews target a progress of rate of 24 rings/day.

When complete in late 2017, the 4.65m i.d. tunnel will be the largest wastewater tunnel in Scotland, with a storage capacity that provides extra to spare.

This is work that the tunnel crews relish. “It is fantastic to be working on such an important project,” said Rushe, who is 25 and from Birmingham. “I enjoy working in tunnels. It is technical work in these conditions and one I enjoy every day. You become used to the confined space and we have everything we need down here to work our shifts.”

The machine is on schedule and expected to complete its journey and emerge at the Queen’s Park reception shaft in the Summer of 2017, after which the new tunnel will be connected to the existing network and the project completed by about the end of 2017.

Inevitably, as the tunnelling progresses and the TBM gets further along its 5km long route, the journey to work for the crew will also get longer. In the final stages of the drive, the commute will take almost 30 minutes.

At the end of each day, the workers make the journey in reverse, taking the train back from the TBM to the access shaft, passing Saint Barbara, climbing the stairs and checking out at ground level.

Like all commuters, the gang are delighted to head home, eat, relax and sleep….and get ready for another day at their special work place tomorrow.

The £100 million Shieldhall project is part of the biggest upgrade in the Greater Glasgow wastewater infrastructure since Victorian times. When complete, the tunnel will run from Craigton to Queen’s Park, under Bellahouston and Pollok parks, and will help improve river water quality and tackle flooding in the south west districts of Glasgow.

The project matches the investment by Scottish Water and in an alliance with Caledonia Water, for improving water supply infrastructure for their Ayrshire and Renfreshire service areas, which also includes a TBM operation to pass under a main line railway corridor.