Surface water drainage is not the most visible element of a new road scheme – after all, it’s almost entirely underground. But it is vitally important to any road and it’s one of the first priorities before work starts on the carriageway.
At Costain’s £59 million Harbour Way contract (the final phase of Neath Port Talbot County Borough Council’s Peripheral Distribution Road (PDR) scheme) the drains are required to do more than simply direct surface run-off into the nearest water course. As with all projects today, the system is designed to provide attenuation in the event of heavy rainfall to prevent flooding and avoid excessive surcharge of the local water courses.
For this 4.5 km long stretch of dual carriageway linking the M4 motorway to Port Talbot and the docks, a high-capacity attenuation system, extending for about 2 km of the road’s length has been installed using precast manholes and special concrete pipes supplied by Dutch precast manufacturer Kijlstra.
Compared with the traditional method of on-site construction using a combination of precast rings and in-situ concrete, prefabricated concrete elements are a novelty. They are designed to be lifted straight into the excavation and mated with the pipe connections with virtually no manual labour beyond that needed to align the units.
And although a common sight for the past two decades in Kijlstra’s native Netherlands (a country more or less built by drainage engineers) they are now becoming a more familiar sight in the UK.
In an industry renowned for its dogged adherence to the “tried-and-tested”, Kijlstra has had to work hard to sell the concept of prefabricated manholes, headwalls and associated products to British contractors and engineers. For a start its manholes are square, not round – a concept quite alien within these shores.
The decision to award Kijlstra the nearly £1 million contract to supply precast manholes and pipes on the Harbour Way project followed their successful deployment on another Costain site in South Wales – the £90 million Church Village Bypass near Pontypridd, completed two months ahead of schedule in September 2010.
Kijlstra won the Church Village contract only after sales engineer Wieger Faber challenged the construction team to dig two holes and install Kijlstra manholes in one and a convential manhole in the other. “Ours was installed and backfilled before they’d even started to pour the concrete base for the traditional manhole”, claims Mr Faber. “After that, the project manager just said alright, we’re using the Kijlstra manhole.”
Specialist contractor Flowline Civil Engineering, which worked with Kijlstra and Costain on the Church Village Bypass, was an instant convert to the pre-fabricated manhole concept. So when Flowline joined Costain on the Port Talbot project, the company pushed hard to get the traditional drainage design changed in favour of the Kijlstra product
“Kijlstra wasn’t specified on this project” comments Costain project manager John Skentelbery; “the client had specified traditional manhole rings. But we had used Kijlstra on Church Village and Flowline had praised the system”. Mr Skentelbery had no personal experience with Kijlstra, not having worked on the Church Village Bypass, but was soon convinced of the system’s benefits.
“We chose to use this system on all the attenuation drainage [up to 5 m deep]. Health and safety was the big issue here. Flowline were working in made ground with a high level of industrial contamination and a high water table. Anything that could minimise the need to work in the trench had to be worthwhile”.
On this project, Kijlstra’s precast manholes were used, together with 1,950 m of 1500mm diameter precast pipe sections. And although nationally standard products both manholes and pipes were tailored to the client’s precise requirements (a process Kijlstra calls “customised mass production”).
“The pipes were slightly modified in that they were the standard profile with a special low flow channel moulded into the base” explains Mr Faber. The manholes were also cast with a bespoke bench profile to provide the low flow channel.
This was only possible due to the fact that Kijlstra was involved in the design development well in advance of work starting on site. “Kijlstra’s role was to optimise the design and look for cost savings” says Mr Faber, who spent three days a week on site during the three weeks prior to work commencing.
Mr Faber was the link between the project and the factory, finalising designs, ordering the manufacture and co-ordinating the delivery to site. This enabled the site team, made up of the client, main contractor, sub contractor and Kijlstra, to value engineer the drainage design, eliminating a number of manholes from the original design making savings in the region of £20,000.
While site safety and ease of installation were the main reasons Flowline pushed for the prefabricated drainage option, speed of installation is a major advantage as well as inherent cost benefits too, says Flowline managing director Keith Snape: “We knocked about two weeks off the programme” he says.
Wieger Faber’s ongoing involvement with the project means that he has been visiting the site once or twice a week since work commenced. And this is not unusual on a job of this size, he says: “We would expect to put an engineer on this job. It’s expensive, but the benefits for everybody involved are huge. All our sales people are engineers; they don’t just drop a brochure on the table – they get involved. And the earlier we get involved with a project, the better.”
Harbour Way is the largest transport project in Wales since the completion of the M4 motorway in 1993.
It will provide a 4.5 km link to the M4 at Junction 38 at Margam to enable economic regeneration of the area and improve access to west Wales. It will also improve access to Tata steel and the port, as well as easing local congestion on the M4 and provide a high quality gateway to the town centre and enable environmental improvements on the A48
The project’s £107 million funding is made up of £56.2 million from the Convergence European Regional Development Fund and £50.7 million Transport Grant from the Welsh Government.
Work on the pre-earthwork drainage system commenced in March and will be completed in October. The road is due to open in the autumn of 2013.
Kijlstra’s early involvement is not unique on the Harbour View project. Even before the main contract had been awarded the client, NPT, had worked closely with Costain and their supplychain in the early contractor involvement phase (ECI) to reduce the original tender price by almost a fifth.
“Costain were first awarded a ‘professional services contract’ in advance of the main contract” explains Rhys Griffith, project manager for NPT. “The works contract itself was to be awarded subject to funding being available and the project meeting budgetary constraints” he explains.
“The ECI phase came on board with a public inquiry pending” continues Mr Griffith. “The route was already decided and the scheme was well developed before the contractor was appointed”.
Value-engineering cost reductions to the tune of £15 million helped to ensure the project went ahead and secured its funding from the Welsh Government
But to achieve this, the team had to look at the whole scheme again in order to find opportunities for cost reduction.
Other cost-saving solutions included the use of reinforced earth in place of the piled foundations originally specified.
“We used them mainly for quality and safety reasons” explains John Skentelbery. “But with this system you can build manholes in a couple of hours which would take you days traditionally” he says,