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Glencorse Water TreatmentWorks. Sustainable andinvisible - a golden combination

The construction team building the newGlencorse Water Treatment Works [WTW] inScotland are using camouflage techniques thatwould rival Harry Potter’s invisibility cloak intheir quest to hide the 10 hectare site in thePentland Hills above Edinburgh.

But the skills of Design and Build Contractors, Black &Veatch in conjunction with geotechnical experts Maccaferri,are more practical than magical. Their combined wizardrywill give Scottish Water a state of the art sustainablefacility, providing Edinburgh with more than 70% of itswater needs, which will be almost invisible to walkers andresidents in the surrounding hills.The Glencorse WTW will provide drinking water to around450,000 Edinburgh and Midlothian residents and has beencommissioned by Scottish Water to replace the two ageingfacilities of Fairmilehead and Alnwickhill, which had servedthe area for more than 100 years.The treatment plant’s setting, adjacent to the PentlandsRegional Park, 7.5 km south of Edinburgh, required carefuldesign and planning to reconcile the very large buildingsand reservoir with the surrounding area. The solution wasto effectively “bury” the works, into a carefully re-profiledlandscape, created by placing thousands of cubic metres ofexcavated material behind massive retaining walls.Glencorse comprises four principal structures: An IntakePlant which receives raw water from three neighbouringreservoirs; the main Water Treatment Building; a smallercontact-tank building and a massive, Clearwater StorageTank measuring 200m x 90m x 7m deep.By completely burying the Clearwater Storage Tank anddesigning a low aspect Treatment Plant incorporating whatwill be the largest grassed roof structure in Scotland, theinstallation will be one of the best hidden and mostsustainable construction projects in the country. “The wholeidea is zero visual impact” According to John Marshall,Contract Manager for Black & Veatch. As well as this, by locating the WTW at the elevated site ofGlencorse, Scottish Water was able to use gravity ratherthan energy hungry pumps to drive water supplies to pointof consumption. Another benefit of the gravity flow wasthe ability to generate 25% of the site’s electricity need byinstalling a turbine to harness the water’s kinetic energy.One of the biggest challenges faced by the constructionteam was the creation of a series of retaining walls up to9m high, required to support the huge quantities ofreclaimed fill material used to landscape the south and eastsides of the plant. For this, Black & Veatch brought in Perthbased Maccaferri Construction to provide design andinstallation expertise.Maccaferri proposed a network of mass gravity andreinforced soil structures, principally comprising their stonefilled Gabion Terramesh units in combination with highstrength uni-axial geogrids sandwiched between layers ofcompacted back fill, all in accordance with BS 8006: 2010,Code of practice for strengthened/reinforced soils andother fills.The largest of the five walls defines the western andnorthern perimeter of the access roads and turning areasfor articulated tankers and chemical delivery vehicles whichserve the works. Here the 9.0m high, near vertical structureabuts the Intake Plant then sweeps north around thevehicular turning head before following the north east wallof the Treatment Building.The Maccaferri Gabion Terramesh system forms a hardfacing to the wall and consists of a one-piece soilreinforcement geogrid with an integral gabion fascia unit.This system, including the reinforcing geogrid, is made fromdouble twisted steel wire mesh. The mesh is heavilygalvanised with an additional tough PVC sheathing toprovide a long design life. Each Gabion basket, 2.0m x 1.0m x 1.0m, has locallysourced red basalt, [200-100mm] hand placed to the

exposed face. This creates a crisp and consistent faceprofile with clean lines and uniform visual texture. Thebaskets were then mechanically back filled with similarmaterial.Behind the wall, varying lengths of Maccaferri Paragrid80/05 uni-axial geogrid reinforcement were placed andoverlain in 1.0m lifts, to coincide with the Gabiondimensions, with mechanically compacted fill to form thehigh-strength, reinforced soil structure. A filter fabric layerwas also placed against the back face of the gabion units toprevent migration of fines from the backfill.Allan Rice of Maccaferri. explains. “The main retaining wallsat Glencorse are ideally suited to the use of GabionTerramesh system as the structures are in an area of upfilland there was a requirement to use site won glacial till asstructural fill. As well as this, the walls were designed witha face angle of 6º from vertical to minimise land-take”A Gabion Terramesh wall is constructed in a similar mannerto any modular walling system with subsequent coursesplaced on top of the preceding, backfilling as buildingprogresses. Geogrid is incorporated as a reinforcementmedium which causes the wall and the retained material towork as a single physical mass with immense strength anddurability.According to Maccaferri, their double twist mesh gabionwalls can accommodate larger differential settlement thanmost retaining structures and are suitable for reinforcedsoil retaining structures of almost any height. The wallshave the aesthetics of a gabion with the economicadvantages of a reinforced soil structure.In addition to this, the long term durability andmaintenance free nature of the BBA Approved system wasseen as a significant benefit to the Client in terms of savingsto long term operational costs. In other areas of the Glencorse site, where walls below3.0m high were required, traditional Maccaferri Gabionunits [without integral geogrid tails] were used as massgravity structures, rather than reinforced soil installations.Here the physical mass of the stone filled units wassufficient to retain the back-filled material and no geogridreinforcement was required.Construction of the Glencorse WTW began in July 2008 andis due for completion in late 2011. The £130m scheme isthe largest capital project commissioned by Scottish Waterand has been described by Professor Paul Jowett, Chairmanof the ICE, Institution of Civil Engineers, as being “ not onlyan exemplar project in terms of critical infrastructure butalso in terms of sustainable development and carbonreduction”All the Maccaferri retaining walls were built by thecompany’s specialist installation subsidiary MaccaferriConstruction.

Geotechnical specialists Maccaferri isbuilding a series of earth retainingwalls at the new Glencorse WaterTreatment works in Midlothian. Whencompleted, they will support thousandsof cubic metres of soil being used in thecomplex re-landscaping project whichwill effectively hide the £130m plantfrom walkers and residents in thebeautiful Pentland Hills, south ofEdinburgh.

The Maccaferri Construction team is building a series of earth retainingwalls at the new Glencorse Water Treatment works in Midlothian.

Picture Above : Each of the Maccaferri Gabion basket, 2.0m x 1.0m x 1.0m,has locally sourced red basalt, [200-100mm] hand placed to the exposedface.

Main Picture: Maccaferri proposed a network of mass gravity and reinforcedsoil structures, principally comprising their stone filled Gabion Terrameshunits.The largest of the five walls defines the western and northern perimeter ofthe access roads and turning areas for articulated tankers and chemicaldelivery vehicles which serve the works. E info@maccaferri.co.uk

W.www.maccaferri.co.ukT 01865 770555

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