SuDS Retaining Wall Case Study

Attenuation Pond, Webwall Geocell, Bellway Homes, Nottingham, UK

Project Information

Project Description

Bellway Homes developed a new northern suburb of Nottingham on a greenfield site near Arnold.

The Challenge

Typically, planning consents are granted based on SuDS retention equivalent to a green field site. For reasonably large developments, such as this, the volume of water accumulated from rain 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 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.

The Solution

ABG offered Webwall® geocell as it uses locally won materials to stabilise weak or low cohesion soils. Laid in horizontal layers, infilled and compacted using site won materials, Webwall® geocell was shaped to fit local contours and fitted neatly around the outfall structures. This avoided the costly importing of aggregates and reduced the impact on the environment from the extraction and transport of aggregate to site. During build up and filling, the front cells are filled with topsoil to encourage growth in the front cell 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. Calculations showed that layers of Abgrid geogrid were needed for wall heights above two meters.

As these 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® geocell to provide drainage for ground water flows to prevent saturation of the reinforced section of the structure.

The Abgrid geogrid alone 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 to specification and will form a green civic amenity in the midst of a new urban development.

ABG Webwall geocell, Fildrain drainage geocomposite & Abgrid geogrid used in a steep sloped green wall application.