Construction is well underway on a massive project to upgrade a congested stretch of trunk road in Nottinghamshire, reports Margo Cole.
The A46 is an important road in the East Midlands. It links some of the region’s key urban centres - including Leicester, Newark and Lincoln - and provides a strategic link between the M1 and the A1. For many years, one 28km section of this route has been a major bottleneck to traffic but that is about to change, as this entire section is being improved in one fell swoop.
Over the years most of the A46 has been widened to dual carriageway, leaving one section, south of Newark, as the only stretch of single carriageway north of the M1. The road is joined by multiple farm accesses and at-grade junctions and, as Highways Agency senior project manager Geoff Bethel explains, “If there is an accident, the road closes completely”.
26,600 vehicles per day
The section of the A46 south of Newark to Widmerpool Junction carries up to 26,600 vehicles a day, of which about 22% are HGVs. Highways Agency figures show that average daily flow on the road exceeds capacity 94% of the time. “Journey times are unreliable, and there is a lot of congestion. It also has a higher than average accident rate,” says Bethel. “This is an important scheme for the Highways Agency.”
Project: A46 Newark to Widmerpool Improvement
Client: Highways Agency
Project cost: Approximately £383M
Main contractor: Balfour Beatty
Designer: URS Scott Wilson
May 2009-May 2012
The scheme he refers to is an ambitious project, valued at between £357M and £408M to build 28km of entirely new dual carriageway, most of it off-line, to replace the old road. Grade separated junctions will replace the old at-grade crossings, and local distributor roads will be built for farm and village traffic.
As a result, says Bethel, journey time reliability should improve dramatically, and “it should be much safer because we will have taken away drivers of slow moving vehicles”.
The Agency has always been keen to push ahead with the project, and awarded Balfour Beatty an Early Contractor Involvement (ECI) contract to build the road back in 2004. A preferred route was announced in 2005, and the planning process started in 2007, but even then it was unclear whether the project would actually go ahead.
“There were no sustainability benefits to using the existing carriageway, and we wouldn’t have met modern standards”
Tony Dixon, Balfour Beatty
Although improving the A46 is important for the economy of the East Midlands, the scheme is too big to be paid for entirely out of the Agency’s regional budget. Proposals to do the work in two halves had been considered but the project was in hiatus when the government stepped in and agreed to fund half of its total cost as part of its fiscal stimulus package to boost the economy in November 2008.
The government money came with strings attached, however. Work had to start almost immediately if the project was, indeed, going to help pull the country out of recession: and, instead of being split into two projects each taking two years, the entire scheme was now to be completed in just three years.
The surprise go-ahead for the project meant the contractor had to get ready to start building in just a few months. “Because the scheme had effectively been put on hold, there was no-one in the Balfour Beatty team,” says Bethel, who goes on to explain that this added a new - and positive - dimension to the job. “Everybody here has been recruited specifically for this scheme - and it’s obvious they all want to be involved,” he says.
Balfour Beatty project director Tony Dixon put together the 160-strong main contractor’s team, starting with a core of about 20 key individuals, then bringing in people they knew and had worked with in the past. “I was concerned, as we increased the staff numbers, about the culture, and whether that growth would change the nature of the organisation,” he says. But actually, we’ve created a better culture than some organisations that have been going for 20 years.”
Britain’s best built road
Dixon, who is committed to making the A46 “Britain’s best built road”, says the team’s culture revolves around “health & safety, teamwork and dedication to meeting customer requirements”. So far, so good: since construction began in May 2009, the job is within budget, the accident frequency record is well below the industry average, and Balfour Beatty has stuck by its commitment to send zero waste to landfill.
And the locals are delighted to see work under way on a scheme they have wanted for years.
Interestingly, road accidents on the A46 have actually fallen by 47% since the work started and, by imposing a 40mph speed limit, average speeds of vehicles on this section have only gone down by 4mph, from 41mph when the speed limit was 60mph to 37mph now.
The new route takes a slightly less direct route than does the existing A46, much of which follows the line of an old Roman road. At times the two come together, but even here the old carriageway is being excavated out and completely rebuilt, rather than simply widened. “There are no sustainability benefits to re-using the existing carriageway, and we wouldn’t have met modern standards,” explains Dixon.
In all there are 22 new structures on the route, including eight grade-separated junctions, 11 overbridges, two underbridges and a major rail bridge. “One of the benefits of ECI is that we’ve been able to rationalise the bridge design, and a lot of them now look very similar,” says Dixon. “Being able to use the same design has clearly had cost benefits, and you go through a learning curve less frequently.”
“We had to come up with something that was definitely going to work, because there was no chance of a back-up plan”
Tony Dixon, Balfour Beatty
The same design has been used for 12 of the overbridges, which are being built as integral structures with steel beams and composite decks, and typically span 30m. They are supported on skeletal abutments made up of 600m diameter and 6m high circular concrete columns built using cardboard formwork - something that is more familiar in the building sector than civil engineering. “This is the first time cardboard formwork has been used for such large columns,” explains Balfour Beatty chief engineer Richard Jones. “We carried out trials to prove it could withstand the concrete pressures.” Dixon adds: “Normally all decisions are done for safety, and the cardboard columns typified that. You can get in and out quickly, and there are less people working at height for a shorter time.”
The columns sit within manhole rings, making the entire abutment structure quite flexible. “You get better moment distribution through the deck, and it means you don’t need such a lot of reinforcement at the corners,” explains Jones. A capping beam is cast on top of the columns to form a bankseat, and the steel deck beams are temporarily rested on top of the bankseat, before being cast into position with the deck to form the integral bridge.
A standard design has also been used for the underbridges, which are also integral structures, but this time are built using full height concrete abutments, precast concrete beams and reinforced concrete deck. At one location - Cropwell Bishop - where the new road is very close to the existing one, the new underbridge is being built using top down construction to improve buildability and safety. “It has eliminated the need for an expensive temporary works support scheme adjacent to live traffic,” explains Jones.
Balfour Beatty and its supply chain partners Lafarge and John Jones have been testing the possibility of building much of the road using machines controlled by GPS and laser, rather than traditional pins and string lines.
“GPS systems on the earthworks machines gives sufficient accuracy for those operations, but we’re trying to move to a point where we can get better accuracy in the other layers of the road construction,” explains Balfour Beatty construction manager Pete Taylor.
“The standard way is to put a pin in every 10m and set the levels then dip across with string lines, but that’s a bit old fashioned.”
Survey equipment and machine control specialist Topcon has been developing a system that can increase the accuracy so that the sub-base can be laid automatically by machine.
If this can be achieved to an accuracy that everyone is happy with, the top two layers of the pavement - the binder and surface course - could go down simply by setting the paving machines to lay a constant thickness of material.
The system was trialled last year, and Balfour Beatty is hoping to get Highways Agency approval to use it for the remaining 380,000t of blacktop that still has to be laid once the paving season starts up again in the Spring.