Haul roads & compounds for solar park, UK

Turning challenges into opportunities: The Higher Stockbridge Solar Park & Naue Combigrid® revolution

Located to the northwest of Dorset, 3 miles south of Sherborne, the Higher Stockbridge Solar Park is being developed on a site comprising a collection of fields, mainly improved grassland, across an area extending to around 80 hectares. The solar farm layout will include a large construction compound, a substation compound, and around 3 kilometres of 4-metre-wide access tracks for the movement of vehicles across the site for initial construction as well as for future maintenance of the ground-mounted photovoltaic solar modules.

Challenge

As there’s no shortage of space at Higher Stockbridge, all vehicles and equipment will be stationed on-site throughout the construction period, and rather than installing temporary haul routes across the site during the construction period, it was proposed that permanent access tracks were completed during the initial stages of construction.

Classified as Grade 4 and Subgrade 3b agricultural land, which represents some of the poorest agricultural land in the county, the task of delivering a robust and stable network of access tracks and compounds for the development was a potential challenge for contractor Aider UK.

The central and southwest areas of the site have superficial deposits of clay, silt, sand and gravel. The bedrock for the whole site is mudstone and sandstone. The soil is recorded as ‘loamy and clayey with slightly impeded drainage’.

“Although obviously well-placed to benefit from sunlight, the site conditions were hardly conducive to road building without importing copious volumes of aggregate to create a sound base,” says Naue’s sales manager for southern England and Wales, Jake White, “and in many areas, excavations prepared for the tracks and compounds quickly transformed into rivers and ponds!”

From soft soil to solid roads: Combigrid®’s transformation at Higher Stockbridge

However, having gained experience of Naue’s products on previous installations, Aider UK were confident that a geosynthetic solution would also be suitable for this project.

“Combigrid® was perfect for this application”, says Jake White. “The amalgamation of a geotextile and a geogrid layer in a single product, simplifies installation on projects where separation, filtration, stabilisation and reinforcement properties are all essential. In addition, the geogrid’s excellent tensile strength at low elongations reduces the depth of the aggregate layer significantly.”

Combigrid® combines a laid geogrid, made of stretched, monolithic flat bars with welded junctions, and a mechanically-bonded and calendared filter geotextile welded within the geogrid’s structure. Combigrid® is used to stabilise and reinforce soils in many fields of infrastructure, environmental protection, and hydraulic engineering applications. Installed directly to a soft subgrade, the composite material acts as a separation layer between fine-grained soils and a coarse aggregate base layer; improving the bearing capacity of the aggregate layer, reducing surface deformation from vehicle movements, and ensuring long-term filter stability and extended service life.

Naue supplied 50 rolls for the project; each roll being 100 metres long and, at 4.75 metres wide, perfectly-sized for the 4-metre tracks.

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