Bellway Homes developed a new northern suburb of Nottingham on a greenfield site near Arnold.
Typically, planning consents are granted based on the SuDS retention equivalent of a green field site. For reasonably large developments such as this, the volume of water accumulated from rainfall run-off would mean sizeable ponds, using up valuable building land. The designer proposed a basin with steep slopes to save space; the lower portion at 60 degrees and the upper at 30 degrees. The challenge was to provide a steep wall with a green finish which can withstand surface run-off erosion and be structurally sound at minimum cost.
ABG proposed Webwall geocell since it stabilises locally won weak or low cohesion soils. Laid in horizontal layers, infilled and compacted using site won materials, Webwall geocell was shaped to fit neatly around the contours of the site and the outfall structures. This avoided the cost of importing aggregates and reduced the impact on the environment from the extraction and transportation of aggregate to site. During build up and filling, the front cells are filled with topsoil to encourage growth in the front cells once construction is complete. Vegetation on the face gives a pleasing visual impact and improves system longevity.
The wall needed to be stable during construction and service with calculations showing that layers of Abgrid geogrid were needed for the wall height above two meters.
Since the ponds are at the bottom of a series of swales, there will be a higher water table at times of heavy rain. Strips of Fildrain drainage gecomposite are included behind the Webwall to provide drainage for ground water flows and prevent saturation of the reinforced section of the structure.
The Abgrid geogrid was used to reinforce the upper slopes and the face was protected from surface erosion with Erosamat Type 1 erosion control matting while vegetation established. The overall construction was finished on time, within budget and specification to form a green civic amenity in the midst of a new urban development.
The ABG Service
ABG offered a full turnkey design, supply and installation package (installation by ABG subsidiary, ABG Installs). This package was chosen based on the technical proposal, meeting the construction program and ultimately cost effectiveness.
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