WET News

14 WET NEWS SEPTEMBER 2014 Mendip aqueduct goes into rehab The work has been confined to small areas around the shafts that give access to the aqueduct projEcT SpEcS • Rehabilitate and improve the 170-year old Mendip aqueduct to ensure it can continue operating for the foreseeable future • Install GRP (glass reinforced plastic) liners as well; concrete spray lining; and grout the existing tunnel • Construct shafts in order to access the aqueduct from the surface • Improve existing facilities at the Line of Works system to help operate and maintain the network more safely and efficiently • Bristol Water's Mendip aqueduct has been carrying untreated water from the River Chew for 170 years. What happened when it needed to be spruced up? T he city of Bristol is one of the largest cities in the UK, with a core population of more than 400,000. It is not sur- prising that Bristol with its great international trading history, cosmopolitan population and a significant tourist, cultural and engineering heritage has some of the oldest and most interest- ing infrastructure serving it. The provision of drinking water to Bristol has long been of great importance to the success of the city and this requirement is the responsibility of Bristol Water, the independent private water company established in 1846 and which serves some 1.2 million population in the Bristol area. As part of this responsibil- ity, Bristol Water has to main- tain the major and significant Mendip aqueduct. At almost 170-years old, the aqueduct is an excellent example of large scale Victorian engineering. The aqueduct has been carrying untreated water from the source of the River Chew at Chewton Mendip to the reservoirs and water treatment facility at Bar- row Gurney since it was con- structed during the mid-1840s, and was one of the first struc- tures to supply fresh drinking water to the city. As might be expected of a structure of this age, it has reached a point where it is in need of some refurbishment. In a project known as the Line of Works Rehabilitation and Improvement Scheme, Bristol Water, together with Black & Veatch, developed a rehabilita- tion programme designed to ensure that the aqueduct was able to continue operating for the foreseeable future. Once the design was confirmed the deal to complete the works was awarded to contractor Kier MG. As a significant part of the planned works was to utilise trenchless lining techniques these works were subcontracted to rehabilitation specialist con- tractor Matt Durbin Associates. Functional life The project, which will ulti- mately cost a total of £8M, will add a structural lining within the aqueduct in order to strengthen it, extend its func- tional life and improve the flow of water through the structure. The work was designed to be confined to small areas around the sha–s that give access to the aqueduct and is largely con- fined to private land through the Litton Area and in East Harptree (located in Harptree Coombe) as well as West Harptree and Chew Stoke. Whilst the majority of the 19km-long aqueduct runs underground at depths of up to 40m through predominantly sandstone and limestone strata, it does run on surface at Harp- tree Coombe, crossing Watery Lane near Winford and finally as a backdrop to the Village of Winford itself. The whole rehabilitation pro- gramme was planned to be com- pleted over three years in 2012, 2013 and a final stage in 2016. The rehabilitation work involves using a variety of tech- niques including: l The installation of GRP (glass reinforced plastic) liners l Concrete spray lining l Grouting of the existing tunnel NEEd To kNoW • The depths and access restrictions associated with the refurbishment works prohibited cost- effective use of remote refurbishment techniques • The 19km-long aqueduct runs underground at depths of up to 40m through predominantly sandstone and limestone strata • The contractors worked in collaboration to organise an emergency rescue scenario involving the specialist USAR and HART teams from the emergency services • Apart from the new shafts, access from the surface was restricted to the use of existing ones, which were typically 1,200mm diameter, with many of the deep shafts only being 900mm in diameter ThE vErdicT • Both phases of the project finished to programme • Engineering solutions were offered and implemented to overcome the isolation and infiltration challenges that arose on several of the sections. ONSITE AQUEDUCT REFURBISHMENT TEchkNoW • The lining works around the liner segments was completed with a Colmono CX410 high shear colloidal mixer • Both wet/dry spray techniques were utilised depending on the surface condition prevailing at the location of the installation • HDPE invert pieces were placed into the aqueduct • Stainless steel mesh was used around the crown of the tube onto which was sprayed a final surface treatment of 40 Newton micro-concrete

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