Scott Harvey takes a look at a £130m, PPP school campus construction programme in the Scottish Highlands and how the basic process of earth, cut, shift and retain has contributed to it's successful implementation.
27/11/2008
The construction programme is part of Perth and Kinross Council’s Schools Investment in Learning Initiative [IIL] and involves the design, build, finance and operation of six school campuses in the east of Scotland.
The IIL programme is the council’s biggest and most significant to date and will deliver the six campuses to local communities in Perth & Kinross, providing modern, high quality facilities for learning, teaching and community use.
Axiom Education Ltd, a PPP [Private Public Partnership] consortium comprising international Bank, ABN AMRO; facilities management provider, Mite and a major UK contractor, has joined forces with Perth & Kinross in a 30 year contract to jointly design, build finance and operate the schools.
The six learning campuses will include two all-through (nursery/ primary/secondary) schools, two primary and two secondary. Each will replace existing facilities which have reached the end of their working lives and will serve the communities of Breadalbane, Blairgowrie, Strathearn, Loch Leven, Glenearn and North Inch.
Work on the campuses began in December 2007 and is being phased over a four year period with completion of the final works due in October 2011.
One of the particular challenges facing main the contractors was the varying site topographies. On four of the sites they had to undertake major re-profiling. Sloping areas had to be levelled off and this involved the construction of several retaining walls to create large flat terracing for buildings or recreational areas.
In conjunction with Maccaferri, the contractors devised a clever, cut-and-fill scheme which meant that all the excavated material was retained on site and re-used to build up low areas behind the retaining walls. The cost and environmental economies were significant.
Visual impact on the surrounding landscape was also of major concern and the use of retaining walls with an environmentally sympathetic, green face finish was specified on three of the four sites.
Maccaferri’s Green Terramesh, an innovative formwork system that creates a “green” faced reinforced earth retaining wall when used in conjunction with polyester geogrids and compacted back fill, was specified for walls built at the North Inch, Breadalbane and Blairgowrie campuses.
Green Terramesh units include a factory-fitted, welded-wire ‘lost shutter’ formwork with a pre-set face angle. No external formwork is needed so construction is quicker and more economical. Significantly, it also provides a crisper, natural looking face, when compared with traditional geogrid wrapped-face structures built with external and removable, formwork.
Bio-degradable vegetation matting, fitted to the face of the unit forms a 300mm wide reservoir for top-soil, creating a nutrient-rich environment which promotes rapid vegetation cover, effectively hiding the units, resulting in a natural, green aspect to the slope.
At Breadalbane and Blairgowrie, the Green Terramesh walls support cuts which have allowed the installation of full sized football pitches for the schools. At North Inch the wall was constructed at the low end of a gentle slope and then back filled to maximise the available land.
At the Glenearn and North Inch campus sites, more substantial retaining structures were required and walls constructed using stone filled Gabions, also from Maccaferri, were selected. At Glenearn, the wall supports a local council transport yard which backs onto the site. At North Inch the wall will support the rear gardens of adjoining properties.
