ACO were asked to provide a highway drainage system for a road tunnel under the sensitive environment of the Devil’s Punchbowl in Surrey, to meet the ambitious performance and environmental targets of the project.
1. Product to meet tough environmental and low-carbon construction targets.
2. Product to meet Highways Agency performance standards.
3. Ability to supply bespoke elements to complete the project.
The improvement scheme for the A3 around Hindhead has been under consideration since the 1980s. Such is the environmental importance of the Devils Punch Bowl – a stunning natural amphitheatre that sits next to the town – that is has taken many years to develop a scheme that strikes an appropriate balance between the needs of traffic using the major arterial route into London and the conservation requirements of the area – one that has been designated a Site of Special Scientific Interest (SSSI).
Improvements to the A3 were necessary to relieve severe congestion, cut journey times and improve traffic safety. With an average of 30,000 vehicles using the existing stretch of single carriageway road through Hindhead every day, the area had become a regional hotspot.
In 2006 the Highways Agency received approval from the Secretary of State for Transport to proceed with the tunnel project. Together with partners Balfour Beatty Civil Engineering, major works began on the £371 million project in January 2007.
The tunnels’ drainage system protects users in any event where high volumes of liquid are discharged onto the road surface. Ensuring the rapid removal of potentially hazardous chemicals or fuels from the surface and safely moving them away from the site without any leakage into surrounding soil and groundwater were critical to the design specification.
“A high capacity combined kerb drainage system would give the hydraulic performance needed, but there were a number of factors that had to be taken into consideration,” says Daniel Machnik, Senior Buyer, Balfour Beatty Civil Engineering. “The project’s environmental and low-carbon construction targets would need to be met, the system would have to comply with all the Highways Agency’s performance standards and, critically, we would need a number of bespoke elements to be manufactured that would allow the system to tie-in seamlessly with the tunnel’s below-ground pipe network.”
Both Balfour Beatty and project design engineers, Mott MacDonald were familiar with ACO KerbDrain® combined kerb drainage system. “ACO’s Design Services team worked closely with Mott MacDonald and ourselves on the proposal and produced a well researched, detailed examination of the system’s performance. It gave us the confidence that KerbDrain could handle the worst-case scenario set-out within the specification.”
KerbDrain runs along one side of the carriageway in each tunnel.
As Daniel Machnik explains, there were other reasons reinforcing Balfour Beatty’s decision to select the KerbDrain system: “KerbDrain’s one-piece design would give us an advantage on site as it would be easier to handle and quicker to install than a two-piece unit. It would also be more straightforward and cost effective to seal.”
“Environmentally, we would benefit from Vienite® – the recycled and recyclable material that KerbDrain is manufactured from and which uses only locally-sourced materials to minimise its carbon footprint. It carries the BSI Kitemark, giving us absolute assurance that all the products meet the latest Highways Agency requirements and guarantees a minimum Load Class D installed performance.”
“We also worked with ACO Technic, ACO’s bespoke product development division, to look at developing a number of special components. These included the gully units that would allow the system to connect to the tunnel’s carrier pipework. Its team quickly determined that our proposals were feasible and realised designs that could be manufactured to our tight tolerances, delivery schedules and budget.”