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www.managingwater.co.uk DRAINAGE SYSTEMS SUDS in Highway Drainage


Innovative Hybrid SUDS System Provides the Solution for the A3 Road Improvement Project


Four separate soakaway structures, including a circular modular cell installation, manage surface water run- off on the A3 road improvement scheme at Hindhead, Surrey.


The £371 million A3 Hindhead road project, undertaken on behalf of the Highways


Agency required an


innovative yet heavy duty soakaway solution. Polypipe WMS worked closely with Balfour Beatty to provide a solution using its Polystorm and Polystorm Xtra modular cells, creating four separate soakaway structures.


With the first two, relatively simple structures installed in November 2008, in-depth design work then began on the third and fourth soakaway applications. Polypipe WMS was heavily involved in the initial design process along side Balfour Beatty and consultant engineers Mott Macdonald and Atkins.


The third soakaway structure provided a particular challenge in order to meet the required installation depth of 6.5 metres. The innovative solution designed by Polypipe WMS in conjunction with


Polystorm and Polystorm Xtra cells were used to form the fourth structure, creating a six metre wide x 62 metre long structure. Polystorm Xtra cells formed the base layer of the soakaway tank to achieve an installed depth of 4.2 metres. Working closely with Balfour Beatty, Mott Macdonald and Atkins, a number of 750mm diameter 'wicks' were designed using a 750mm collar and structuredwall pipe with a gravel filling. This provides a 30% void ratio and improves the flow of surface water from the soakaway structure down to the permeable soil strata at 15 metres.


Daniel Machnik, Senior Buyer for Balfour Beatty Civil Engineering was impressed with the innovative water management solution provided by Polypipe WMS. "This project has


Balfour Beatty, used Polystorm cells installed in a circular, concrete-lined tank. Granular material was then used to fill the gaps and maximise the performance of the soakaway. A 1500mm catchpit was also used to divert excess stormwater to the soakaway structure.


demonstrated the Polypipe WMS 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."


Polypipe WMS also undertook further design work for £200,000 worth of cable protection products supplied for the project. To improve the installation times


of the cable protection within a tunnel section of the project, Polypipe WMS suggested a large bank of sealed ducts in 94 and 150mm diameter were installed using its 150mm Ridgidrain Plus pipe with integral sockets. As part of an overall commitment to reducing its impact on the environment, Polypipe WMS also implemented a recycling scheme on-site, collecting off-cuts of pipe for re-use in its manufacturing process.


SUDS used for £375m A46 upgrade


The Highway Agency will be using a sustainable drainage solution (SUDS) as part of its £375m dual carriageway upgrade.


The works by contractor Balfour Beatty Civil Engineering (BBCEL) will see the development of 28km of new dual carriageway on the A46 in Nottinghamshire, while the SUDS scheme will be used to achieve pre-development surface water run-off.


This is in accordance with Environment Agency guidelines which require flow restrictions to be held at the pre- development rate for greenfield run-off, in order to ease water volumes into local watercourses and control water quality.


Work started on the upgrade scheme in 2009, and is set to be completed by summer 2012.


The A46 between Newark and Widmerpool is one of Nottingham-shire's most congested roads, carrying between 16,200 and 25,300 vehicles a day and the upgrade will improve traffic flow and safety, while by- passing several villages.


The new dual carriageway will significantly reduce congestion and provide a new fast link between the A1 and M1.


However, it was faced with the challenge of doubling the surface area of this trunk road, which would have created unacceptably high surface water runoff.


As a result, Balfour Beatty and consultant engineers, URS Scott Wilson designed a series of 12 balancing ponds with the outfall from each controlled by a hydro-brake flow control device.


The balancing ponds are designed with a permanently wet sump area and vegetated dry sections to ensure optimum entrapment of debris and silt at most stages of inflow.


BBCEL site engineer Steve Sloan, said: "A series of 12 balancing ponds of differing sizes were constructed, accepting flow from between 800 metres to two km of highway. They discharge into many different watercourses along the route, and the Hydro-Brake is widely recognised as the best flow control device for these projects."


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