Water & Wastewater Treatment Magazine
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18 | XXXXX 20XX | WWT | www.wwtonline.co.uk 18 | SEPTEMBER 2018 | WWT | www.wwtonline.co.uk The Works: sewer networks the geology is very mixed and can change rapidly. There's not a lot of tunnels in Glasgow and there's not a wealth of literature regarding the ground." In the face of all these challenges, Scottish Water sought outside expertise through a Costain Vinci joint venture that combined UK and European civil engineering specialists with extensive tunnelling project experience. "There was a recognition from Scottish Water that this project was outwith the skillset of our own internal framework suppliers, so the decision was taken to competitively tender the project," Flanagan adds. Explaining the particular skills of the main contractors, Costain project manager Neil Grosset says: "Vinci's strength is very much in slurry tunnelling. Costain, as well as tunnelling experience, brought the UK element, dealing with the civil construction work and the interfaces with Network Rail and Transport Scotland." The Costain Vinci JV brought in AECOM to coordinate the design of the tunnel and its ancillaries, while Halcrow – later acquired by CH2M, which has itself now merged with Jacobs – worked client-side with Scottish Water to offer guidance. "It was very much the experience of the teams and the tunnel machine operators that ensured this was completed successfully," Flanagan says. The Glasgow Tunnel Partnership, as the group was known, had a co-located office on site and Flanagan adds: "That was a key part for us – ensuring we were all working together. It was all about collaboration and risk management, making sure we were dealing with issues when they arose." For the rail and road crossings, Network Rail and Transport Scotland were invited to work at the office. "There was a lot of time spent with Network Rail," Flanagan says. "We had the approvals in principle in place but then it was down to the engineering capability and how we deliver while keeping the railway safe and operational up above us." As Scottish Water had opted for a gravity sewer, the depth at the opening of the tunnel needed to be relatively shallow, which presented particular problems when crossing the first railway line. Grosset says: "The fall between the two connection points is only 4m, so you've got a 4m fall over 5km of tunnel, and the Paisley Canal railway was the point where we had the lowest cover between the crown and the existing ground level. Having a 4.7m diameter tunnel where you've only got 3.7m of cover is quite a challenge. "The ground conditions under the railway were also challenging." Flanagan adds: "A lot of work was put into satisfying Network Rail that we had an engineering solution to be able to deliver that piece of work safely." There was a sizeable task in managing disruption to the public, too, The TBM was produced by Herrenknect but Scottish Water spent three years on a communication campaign to raise awareness and forge links with local community organisations. "One of the key aspects was that very early on we recognised we were going to be disruptive to that local community," Flanagan says. "We actually built a new haul road into the site, which took away a lot of that major traffic problem from the local community. Doing that prior to commencing our work gave us a lot of credibility. "It wasn't just the tunnelling work though. Before the project could get up and running, we spent nine months infilling historic mine workings in three disparate areas along the route. It was a very disruptive bit of work – noisy, dusty – and that was the first bit people saw. "Trying to get over that hurdle was difficult, but the record speaks for itself – we've done the largest communications campaign Scottish Water has ever undertaken and had no complaints from the local community." With minimal disruption, the Shieldhall project has – in Roseanna Cunningham's words – "brought a 19th century structure into the 21st century", and its success owes much to the initial planning phase. "MGSDP set the direction for the project," he says. "It's all of the stakeholders collectively agreeing what is required via value management studies – it's effectively a co-owned solution. "That model of local authority working alongside the regulator and ourselves is now seen as a blueprint and has been starting to roll out into other Scottish cities as well. It means there's no question – everyone's bought into the solution and agrees it's the right solution. "That brings about efficient investment for the public pound." • The tunnel boring machine – weighing 1,000 tons and measuring 180m – was delivered to Scotland in sections by sea from German manufacturer Herrenknecht • Named Daisy the Driller by a local schoolboy, it was launched on 6 July 2016 and spent 15 months tunnelling at a speed of around 2mm per minute, using a 5.51m cutting head with 25 cutters at the front • The TBM had to cope with geology that varied from very so soil to hard and abrasive sandstone and mixed faces • It was a slurry shield TBM, which enabled the team to control the pressure at the tunnel face and support the ground in front • The Costain Vinci JV needed to put in a significant amount of work on the design of the machine to ensure it could cope with the Glasgow geology. For example, due to the prevalence of old mine workings, the TBM was not only equipped with gas detectors but allowed any gas that infiltrated the working chamber to be collected and diverted through the slurry circuit or released through the ventilation system • Because of the mixed geology and shallow depth, the project required a vast range of techniques: piled sha s, top-down constructed sha s, sprayed concrete linings, pipe jacking, grouting, cut-and-cover and bored solutions • More than 3,200 six-segment concrete rings were installed • Throughout the course of the tunnel work, more than 500,000 tonnes of earth, stone and clay was excavated, with the Glasgow Tunnel Partnership able to recycle over 90 per cent of that material either on the project itself or elsewhere • THE TUNNEL