Water & Wastewater Treatment Magazine
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www.wwtonline.co.uk | WWT | XXXX 20XX | 17 170-year-old structure was found to have settled by over 160mm from the original constructed level, thereby encroaching into the kinematic envelope of the London Underground trains below. The 2.1m tall by 1.7m wide sewer was originally built by Joseph Bazalgette in 1848, seven years before the first section of the London Underground was opened to the public. The two structures intersect near Baker Street tube station. At this location, the sewer is supported by two primary cast-iron beams spanning between pad-stones embedded within the brick walls of the London Underground tun- nel. The sewer's degradation at this location was attributed to the settlement of the London Underground tunnel beneath. Closing the tube line to repair the sewer from below ground would have cost around £1 million per day, which was not an option. Similarly, closing the busy junction between Marylebone Road and Baker Street to repair the sewer from above would have caused major disrup- tion for five or six months. Stantec's design solution involved a stainless-steel bridge and integral liner. These were constructed offsite, disman- tled and rebuilt inside the sewer, aŒer being lowered underground one piece at a time through a narrow manhole. "Our team's ingenious solution in- volved strengthening the sewer from the inside," Dr Neal Edwards, KSP lead designer and technical director at Stantec, says. "We designed and constructed a 'thin', lightweight bridge structure composed of modular super duplex stainless steel trusses which could be assembled inside the sewer, with a tailor-made fibre rein- forced plastic liner constructed within the steel structure to provide a conveyance medium for the effluent flow. "All project components were spe- cifically designed to be as lightweight as possible, modular and less than 2 metres in length to allow access through a single 600mm by 750mm manhole. The design and construction of this massive jigsaw puzzle demonstrates exceptional project execution, with every component fitting together with millimetre precision." Digital technology was invaluable in the provision of design data relating to the final fit of the proposed solution. It allowed the design team to accurately assess interfacing structures plus space limitations to minimise 'fit' issues and construction time inside the sewer. The digital model was shared with critical suppliers, so everyone worked within the same digital environment. Additionally, virtual reality and aug- mented reality visualisation techniques were adopted. "This approach familiarised Skanska and Balfour Beatty Construction teams www.wwtonline.co.uk | WWT | OCTOBER 2018 | 17 with the environment and the work prior to construction to minimise risk and improve health and safety considerations during construction," Skanska project manager Asad Hanfi says. Dr Edwards says: "This degree of preci- sion engineering resulted in the solution being absolutely aligned with the surround- ing environment. In addition, the choice of materials used were heavily influenced by the environment and requirement for a 120-year design life. The successful execu- tion of this modular approach also means it is repeatable for other major sewers crossing railways where site constraints are extremely challenging." Thames Water's Taylor adds: "The KSP project delivered by the eight2O team dem- onstrated exceptional project execution, client care and stakeholder engagement as well as thinking outside the box when faced with extraordinary constraints. "At £1.5 million per linear metre, the rehabilitation of an old Victorian under- ground pipe bridge could be considered expensive. However, this project not only delivered impressive savings of £23 mil- lion on our AMP6 business plan solution but it involved no rail or road closures. "It also saved over 26 tonnes of embod- ied carbon – equivalent to 100,000m3 of concrete not poured – and has delivered an asset capable of maintaining wastewa- ter operations for a further 120 years." SEWER NETWORKS Trial assembly of the duplex steel truss and liner panels