Aug 18, 2018 Last Updated 8:05 AM, Aug 13, 2018

Interpave discusses an unusual concrete block permeable paving project

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The trade body Interpave discusses an unusual concrete block permeable paving project that focuses on water quality and wildlife, as well as engineering requirements.

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The Hazeley Academy (formerly Hazeley School) is a purpose-built, state-of-the-art secondary school in Milton Keynes. The project incorporates a sustainable drainage system (SuDS) scheme designed by Robert Bray Associates, incorporating extensive areas of concrete block permeable paving.

Although the main building phases were completed in 2007, expansion has continued. Interpave recently revisited the site to explore the positive ecological impacts and long-term maintenance and performance implications of permeable paving and SuDS in areas around the main buildings.

Treatment within the pavement

Here, two hard landscaped areas comprise footpaths, car parking, cycle racks and other paved areas, on land sloping away from the school building. They are surfaced in concrete block permeable paving and asphalt draining onto the permeable paving. Because of the site slopes, the permeable pavement sub-base is divided into compartments by walls extending up from the underlying subgrade to the surface. Water flows from higher to lower compartments via flow control chambers, with access in case adjustment is needed. This provides a retention time enabling biological treatment of runoff with bio-remediation of organic pollutants like oils, milk and animal excrement.

Roof water in down-pipes is also added to the permeable pavement sub-base through filter chambers and then diffuser boxes. At the bottom of the terrace of compartments, water discharges into two wildlife ponds, overflowing into a storm water sewer.

Other, level play areas behind the school are handled in a similar way, with treated, attenuated water transferred under the building, via flow control chambers, where it joins the SuDS management train. Some of these areas were designed to collect rainwater for harvesting.

Monitoring surveys

Bernwood ECS have carried out pre- and post-development monitoring of the Great Crested Newts on the whole Hazeley site from 2002 to 2014, including the two ponds fed from concrete block permeable paving. The surveys show an overall increase in the population of great crested newts and suggest that ‘Favourable Conservation Status’ on site has been achieved.

This project takes a holistic approach and offers an impressive demonstration of concrete block permeable paving providing a controlled flow of clean water for wildlife habitats. The permeable paving provides effective water treatment generally without the need for other SuDS techniques, such as swales or filter strips, minimizing land-take.

At the same time, wildlife is protected with an absence of gulleys and other traps. It clearly shows that permeable paving can be applied to sloping ground, with terraced compartments using flow control chambers, and can also accept roof water and runoff from adjacent sealed paving.

Problem-free

Concrete block permeable paving has also proved to be a problem-free technology over the longer term, with straightforward, non-specialised maintenance. A new case study exploring all these aspects in more detail has just been published, which can be downloaded via the Interpave information resource.

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