Ambitious modern development has seen large diameter plastic pipes successfully used for vital sewerage system components
Current trends in the construction industry towards offsite build and modular construction are enabling large diameter high density polyethylene (HDPE) structured wall products to lead the way in designing and delivering best value solutions. These products are helping solve complex design issues that might otherwise cause additional costs or programme delays and ultimately affect the ability to deliver major projects within budget and on time.
The new town of Sherford in the South Hams, Devon, has 5,500 homes, four schools and over 80,000m² of employment and retail space, and is located 28 miles to the east of Plymouth, between Dartmoor and the south Devon coast. Construction of the new town started in September 2014 following a prolonged 15-year planning phase, with 700 homes completed and habitable by September 2016. The first residents moved in during May 2017.
large pipes at Sherford, Devon
The project is run by Red Tree, with a consortium of housebuilding giants Taylor Wimpey, Linden Homes and Bovis. Red Tree aims to make Sherford a market town with a historic heritage, with responsible 21st century practices such as the implementation of renewable energy. All the houses are designed to be energy-efficient, and much of the energy will be provided by two wind turbines on site.
Installation of the large diameter plastic pipes for the project has been proven to have a significantly reduced carbon footprint than other alternatives on the market, including concrete.
Using the standard Sewers for Adoption discharge figure of 4,000 litres per dwelling day for 5,500 dwellings gives a typical discharge rate of 254 litres per second. To efficiently manage the vast quantities of foul water flowing through the site once the development is populated, Fred Champion Groundworks commissioned a back-up storage tank for Sherford’s foul water pumping station. The vast 3.5-metre diameter, 30-metre long, multi-leg attenuation tank uses 170 metres of plastic pipes, and holds approximately 1,500m3 of foul water.
The tank is much larger than its more standard sized counterparts, which usually hold around 200m3, and it connects directly to the town’s foul water pumping station. The tank was designed and made to the specific requirements of Fred Champion Groundworks, who were responsible for developing infrastructure for the site’s sewerage needs.
The tank was designed and supplied with an integral dry weather flow channel to meet the requirements set by South West Water. The dry weather flow channel is uniquely designed to improve the hydraulic efficiency of the tank in low flow conditions, helping to avoid silting.
The offline attenuation tank was prefabricated, and transported to the site in Devon in one piece prior to installation, vastly cutting down on the amount of time spent positioning the tank in situ; a huge bonus to the contractors who observed stringent scheduling.
The system was also fully accredited to European standard BS EN 13476 - Plastics piping systems for non-pressure underground drainage and sewerage – structured wall piping systems of unplasticised poly(vinyl chloride) (PVc-U), polypropylene (PP) and polyethylene (PE).
Darren Williams, Technical Sales Engineer at Asset International, said: “A site with the scope and scale of Sherford requires significant water management infrastructure, incorporating everything a new town could potentially need, from extensive sewage management structures, to anti-flooding measures.
“The ambition of the developers is admirable and we were only too happy to lend our engineering expertise and top notch product knowledge into developing a foul water storage solution, to aid the water management needs of this expansive project.”