Polypipe in the driving seat for major highways project

Polypipe has supplied some of its most innovative sustainable drainage and cable protection solutions as part of a multi-million-pound project to keep one of England’s busiest road junctions moving.

Main contractor, Galliford Try, specified a fully engineered water management attenuation tank consisting of Polypipe’s Polystorm-R and Polystorm Inspect, Ridgidrain surface water drainage system, Ridgistorm-XL large diameter piping system and Ridgiduct cable protection, for construction of the new underpass and additional vehicle lanes at the A45/A46 Tollbar End Junction on the outskirts of Coventry.

Having successfully used Polypipe’s plastic piping systems for previous large scale projects, Galliford Try tasked Polypipe with providing a holistic solution that would meet the demands of the client Highways England, whilst ensuring quicker, safer and easier installation for contracting teams working by the busy highway. Installation of the products was undertaken by sub-contractor Hillstreet Construction Ltd.

Polypipe’s Ridgidrain in sizes 100-600mm, and its Ridgistorm-XL large diameter piping system in sizes 750mm and 900mm diameters were utilised to channel the stormwater run-off away from the roadway towards the Polystorm attenuation tank. This then provided a geocellular solution, upgrading the surface water drainage capabilities for the busy highway.

Polypipe worked with Galliford Try and their designer Arcadis to redesign the solution by removing the specified gabion baskets which were originally to be constructed by hand into a rectangular trough. The gabion baskets would have posed health and safety risks during both installation and post-installation.

Polypipe produced a safer alternative which included a 900mm RIDGISTORMSeparate modular manifold which linked into the Polystorm-R attenuation tank, to include seven sumps for siltration.

The manifold system is connected at various points to the tank, which allowed for better hydraulic distribution of storm water into the system. Polystorm Inspect were also installed along the full length of the tank to allow for inspection and maintenance activities, which can be accessed via the RIDGISTORMSeparate chambers within the manifold.

The Polystorm-R geocellular tank, manufactured from recycled material, was designed in accordance with CIRIA C680 guidelines, meets the Specification for Highway Works criteria and is capable of attenuating 3,138m3 of stormwater.

Installed by Keytec Geomembranes Ltd, the tank was wrapped in geomembrane to make the tank water tight. This was done through Keytec’s ability to manufacture large membrane panels, allowing for a quicker installation and reduced on-site welds.

Using a buried tank for surface water attenuation ensured that the risk of bird strike beneath the flight path to Coventry airport was removed.

The project had large volumes of surplus earthworks material from other works across the scheme which could have imposed costly removal charges to Galliford Try. However, Polypipe was able to help reduce this challenge by confirming that a large proportion of this excess soil could be loaded on top of the Polystorm-R tank, without affecting its structural integrity. The use of a tank design further assisted with reducing the land take footprints as environmental improvements.

Polypipe’s ability to manufacture products in a controlled factory environment also meant that Ridgistorm-XL large diameter pipe lengths could be engineered to exact stiffness classes to meet ground conditions. The pipe profiles were also engineered to support structural calculations to BS EN 1295, allowing pipes to withstand external loading during the installation process and work with the existing site conditions.

As Polypipe’s plastic piping solutions are up to 94% lighter in weight than alternative traditional products, the handling of its products was much easier and reduced the need to hire heavy plant machinery. The use of the system reduced the time and cost of installation as well as providing essential health and safety benefits when working alongside the busy highway.

Jarrod Parkin, Project Director at Galliford Try, said: “The professional and experienced team at Polypipe meant that we were confident a sustainable water management solution would be engineered and delivered to site within the tight timescales we had to adhere to – an important factor, especially within a highways project, to ensure limited disruption and cost.

“We required a tank which, once installed, could be accessed and inspected, which made the Polystorm system the most suitable choice.”

Andy Cullum, Water Management Solutions General Manager at Polypipe Civils, said: “We’ve seen a recent increase of the specification of plastic piping systems as an alternative to traditional materials, especially in highways applications, and from design to manufacture, our team ensures a fully engineered and sustainable solution for the contractor and end users alike.”