Articles & Case Studies

Hybrid Soakaway System from Polypipe WMS Provides Water Management Solution for A3 Road Improvement Project

Posted: Thursday 17th December 2009

A hybrid soakway solution using the Polystorm and Polystorm Xtra modular cells from Polypipe Water Management Solutions (WMS), the UK’s leading manufacturer of sustainable drainage and water management products, has been installed to manage surface water run-off on the A3 improvement scheme at Hindhead, Surrey.

Working closely with Balfour Beatty Civil Engineering on the £371 million road project undertaken on behalf of the Highways Agency, Polypipe WMS supplied Polystorm and Polystorm Xtra cells as part of the £1 million contract to create four separate soakaway structures, as well as its Ridgidrain structured-wall drainage and cable protection products. Polypipe WMS worked with Balfour Beatty on the project specification to provide a soakaway solution which met the heavy duty requirements of the scheme, with all products supplied through Burdens builders’ merchant.

The first two soakaway structures were installed on the project in November 2008. In-depth design work was carried out by Polypipe WMS on the third soakaway structure which used Polystorm cells installed in a circular, concrete-lined tank to enable an installed depth of 6.5 metres to be achieved, with granular material used to fill the gaps and maximise the performance of the soakaway. A 1500mm catchpit was used to divert the excess stormwater to the soakaway structure. The fourth structure utilised both Polystorm and Polystorm Xtra cells to form a 6 metre wide x 62 metre long structure, with Polystorm Xtra cells used as the base layer to achieve an installed depth of 4.2 metres to the base of the soakaway tank.

Polypipe WMS was heavily involved in the initial design process of the soakaway structures, along with Balfour Beatty and consultant engineers Mott Macdonald and Atkins, to design a number of 750mm diameter ‘wicks’. This involved using a 750mm collar with a gravel filling, enabling a 30% void ratio which improves the flow of surface water from the soakaway structure down to the permeable soil strata at 15 metres.

Further design work was also undertaken by Polypipe WMS for the £200,000 worth of cable protection supplied for the project. A large bank of sealed ducts was installed at the side of a tunnel as part of scheme in 94mm and 150mm diameter. To improve the installation times on this section of the project, Polypipe WMS suggested the use of its 150mm Ridgidrain Plus pipe with integral sockets.

As part of its commitment to reducing its impact on the environment, Polypipe WMS also implemented a recycling scheme on the site, collecting off-cuts of pipe for re-use in its manufacturing processes.

Daniel Machnik, Senior Buyer for Balfour Beatty Civil Engineering commented:

“As a partner of Balfour Beatty we have used Polypipe WMS on several sites, but this project has demonstrated the team’s design service and technical support capabilities. The adaptability of the Polystorm and Polystorm Xtra cells offered an advantage on this challenging scheme and the installation guidance the team has demonstrated on-site has been of great value.”

“A lot of work has gone into creating the appropriate solution for the scheme which resulted in some challenging design work for us,” comments Andy Cullum, Southern Business Development Director for Polypipe WMS. “The initial project specifications utilised a range of our products to meet the requirements of the project. On challenging schemes such as this, our project experience and design and technical knowledge can make a real difference, particularly when it comes to designing and engineering a cost effective, hybrid solution.”

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