CH2M helps Scottish Water, Shieldhall Tunnel reach major milestone

Big enough to fit a double-decker bus inside, Shieldhall Tunnel is one of the most significant infrastructure projects in Glasgow since the Victorian era and will provide 90,000 cubic metres of extra stormwater storage, the equivalent of 36 Olympic-size swimming pools. The increased capacity of the waste water network will improve screening of overflows into rivers and reduce the risk of flooding in parts of the Mount Florida/Toryglen and Giffnock areas.

Appointed by Scottish Water in 2012 to advise on various tunnel options, CH2M prepared the reference design, carried out site investigations and assisted with tender preparation and evaluations. In 2014 the tender was issued, with contact award in 2015. Throughout the process, CH2M provided technical assistance and a site team to supervise the tunnelling works construction. The tunnel is due to be completed in May 2018.

Extraordinary feat of modern engineering
"The Shieldhall Tunnel is an extraordinary feat of modern engineering, which builds on the endeavours of those pioneers who sought to improve Glasgow's waste water network more than a century ago," said Roseanna Cunningham, the environment secretary. "Providing an excellent, effective waste water network which serves our growing communities is vital to the city's infrastructure and environment, now and for future generations."

"With Daisy the Driller having reached her destination, we have completed the most challenging part of the project," said Douglas Millican, Scottish Water's chief executive. "We now move to linking the tunnel to the existing Glasgow waste water network and bringing the whole new system into operation next year."

Navigating through tough geology and mine skeletons
Measuring 140 metres long and weighing 1,000 tonnes, Daisy the Driller tunneled through some of the most difficult and challenging ground conditions in the UK, including mine workings. While tunnelling, Daisy installed more than 3,200 concrete rings (6 segments each weighing over 2 tonnes) to form the tunnel, advancing through the ground at 2 centimetres per minute. More than 500,000 tonnes of earth, stone, clay and other aggregates were excavated, 90 percent of which are being recycled.

The challenging geology conditions ranged from soft clay, glacial till to hard sandstone and mud stone. The cover to the crown of Daisy the Driller was less than 1 diameter in places, making control of face pressure critical. The tunnelling team successfully overcame obstacles, particularly where the alignment crossed beneath Paisley Canal railway line and cover was reduced to less than 1 diameter with soft clay.

The ground beneath Glasgow is riddled with old coal mine workings, some of which are unrecorded.  Before any tunnelling could start, the team had to grout infill in four areas along the alignment, a challenging undertaking. Grouting not only allowed Daisy's safe passage through old mining areas, but also ensured the tunnel's long-term stability. The team used approximately 15,000 tonnes of grout to fill the voids left behind by these workings.

About CH2M 
CH2M leads the professional services industry delivering sustainable solutions benefiting societal, environmental and economic outcomes with the development of infrastructure and industry. In this way, CH2Mers make a positive difference providing consulting, design, engineering and management services for clients in water; environment and nuclear; transportation; energy and industrial markets, from iconic infrastructure to global programmes like the Olympic Games. Ranked among the World's Most Ethical Companies and top firms in environmental consulting and programme management, CH2M in 2016 became the first professional services firm honoured with the World Environment Center Gold Medal Award for efforts advancing sustainable development. Connect with CH2M at www.ch2m.com; LinkedIn; Twitter; and Facebook.

SOURCE CH2M

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