Importance of road/tunnel drainage systems
First publishedin World Highways
ACO drainage systems will play a key safety role at the Hindhead Tunnel
A variety of systems are available for quickly and efficiently removing water from roads as Patrick Smith reports
The presence of water in a highway layer reduces the bearing capacity of the road, and in doing so it also reduces the structure's lifetime. Indeed, the recent extremely cold winter in many parts of Europe has shown that in colder climates there is a risk of frost damage when water is present resulting in costly potholes, so drainage systems performing properly are important in road design.
And while motorists driving along a road see little of such systems, they are an expensive and vital element of the structure where the surface drainage system looks after the run-off water from rainfall. This is where the waterproof surface with a crossfall leads the rainwater to drains. Sub-surface drainage systems safely remove groundwater and water getting in through the pavement's surface.
One such drainage project is at the A3 at Hindhead in County Surrey, southern England, a £371 million (US$603.5 million) improvement project that will complete the dual carriageway link between London and the city of Portsmouth and remove a major source of congestion, particularly around the A3/A287 traffic signal-controlled crossroads.
The new road 6.5km long road includes a 1.8km twin-bored tunnel under the Devil's Punch Bowl, a Site of Special Scientific Interest (SSSI), meaning it is environmentally sensitive.
The project will deliver quicker, more reliable journeys on a safer road, and remove much of the present peak-time rat-running traffic from unsuitable country roads around Hindhead (an average of 30,000 vehicles/day use the existing stretch of single carriageway road through the town). The project also includes the closure of the existing A3 around the Devil's Punch Bowl, bringing considerable environmental benefits to an internationally-prized area.
The client is the UK Highways Agency
and the main contractor is Balfour Beatty
with Mott MacDonald
as designers and Atkins
as the agency's representative.
When complete in mid-2011, Hindhead Tunnel will be the longest non-estuarial road tunnel in the UK, and its drainage system will play a key safety role with ACO KerbDrain helping to meet the demanding highway performance specifications and conservation requirements of the area.
Both Balfour Beatty and Mott MacDonald had worked with ACO Water Management on previous projects and were familiar with its ACO KerbDrain combined kerb drainage 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 more cost effective to seal," says Daniel Machnik, senior buyer for Balfour Beatty Civil Engineering.
"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 [British Standards Institution] Kitemark, giving us absolute assurance that all the products meet the latest Highways Agency requirements.
"We also worked with ACO Technic, ACO's bespoke product development division, to look at developing a number of special components.
The KerbDrain runs along one side of the carriageway in each tunnel, and at each of the 16 passageways that link the two tunnels at 100m intervals, special drop and centre stones lower the kerb profile to the finished road surface level, enabling easy vehicle access and transfer between tunnels.
EnviroDeck from PDS a surface-mounted lightweight, non-metallic composite system
Recycled drainage Pipeline & Drainage Systems (PDS) has supplied its products to many road projects including the M1 West Link, Belfast, Northern Ireland's largest road project, after it had initially contacted the contractor HMCJV to discuss bridge drainage.
The M1 WestLink is a strategic traffic corridor, which forms part of the Trans-European Road Network and the Eastern Seaboard Corridor (identified in the Regional Development Strategy). It is the main access route to the south and west of the Province and to the Republic of Ireland.
At a meeting with the project manager, PDS offered its EnviroKerb recycled kerb drainage for roads, and because of the nature of the contract and the very close spacing of the gully gratings it was found that in certain areas the lightweight kerb drainage offered a cost benefit over the traditional kerb and gully method of construction.
EnviroDeck is a surface-mounted lightweight, non-metallic composite system with colour coding options, and acts as a kerb edge, offering a hollow channel with water inlets to collect surface and sub-surface water.
The company also supplied over 5,000 EnviroDeck units to the impressive 1.2km Upper Forth Crossing at Kincardine, Scotland, which was opened in 2008. It was constructed to link two major routes north and south of the River Forth to reduce periodic traffic congestion in the town of Kincardine. The crossing, the second longest incrementally launched bridge in the world, has 26 spans and weighs more than 22,000 tonnes.
Chris Rothery, PDS managing director said after visiting the site prior to opening: "We worked hard on this contract and had a big input into the drainage design, working closely with the designers and the contractor. It is a fantastic project and we are proud that our new EnviroDeck was selected for the crossing.
The Twinstore system from Turbosider UK can provide high performance stormwater control for highway applications
Sophisticated solutionAn advanced approach to maintenance is helping ensure that the UK county of Kent keeps on top of road drainage.
Kent Highway Services (KHS) has a network of some 8,400km of roads and drains, which requires a fleet of vehicles to maintain and support. In order to keep traffic moving and avoid flooding hazards for motorists, road drainage systems have to be consistently monitored and maintained. Previously this was carried out on a reactive basis, but this has proved to be neither cost effective nor efficient.
To manage this task more effectively KHS needed to capture data about locations and conditions of the drains in order to plan cost effectively for maintenance and repairs.
Using geographic information system technology (GIS), ESRI UK worked with KHS to make this information readily available.
Using ESRI UK's ArcPad solution, KHS can now access and record exact locations of drains and conditions and ensure maintenance is carried out without unnecessary costs.
The GIS technology allows KHS to calculate efficient routes depending on the location and condition of the drains. This enables efficient maintenance, whilst improving the safety of the highways and reducing vehicle mileage.
Tubosider TwinstoreTubosider UK says that its novel Twinstore stormwater tank offers higher performance at a lower cost for than conventional systems.
The patented galvanised, corrugated steel Twinstore system is said to reduce installation costs compared with earlier generation systems, and offers effective stormwater attenuation and drainage capabilities.
Its design is also said to offer structural integrity and easy access for maintenance.
The system is said to work through balancing the ratio between tank and granular backfill and by releasing water through pipe ends into a bed lined with an impermeable membrane. Because of this design, Twinstore is said to reduce overall excavation costs.
Saint-Gobain says that its new ductile iron water pipes offer durability and performance
Water removal BluTop is a range of small diameter ductile iron water pipes from Saint-Gobain PAM UK, that can be used in an array of roadway applications.
The system recently passed tough testing in the UK at a special event held in conjunction with Anglian Water. BluTop pipes were drilled and tapped at 250mm intervals by a team from Anglian Water. The pipes were then subjected to repeated heavy blows with a lump hammer but no fractures occurred, proving the durability of the BluTop range according to Saint-Gobain.
The drilling and tapping was carried out using off-the-shelf Tyco flat-bossed gunmetal saddles and ferrules and standard drilling and tapping equipment carried by most pipeline contractors. Overall service connection time is just 10-15 minutes, confirming the versatility of BluTop.
The company added that using this system can provide leak-free reliability, easy handling, reduced installation costs and high water quality even in contaminated ground. The product is available in 90mm, 110mm and 125mm diameters.