On the face of it, the £20M project to dual the 5.2km single carriageway Attleborough bypass on the A11 in Norfolk is about as straightforward as a modern road scheme can be. True, it has the usual ecological concerns - wood pigeons and water voles, in particular - but main contractor May Gurney knows the area well.
It not only built the original bypass 20 years ago, it was also responsible for the recent stretch of dual carriageway immediately to the west (NCE 14 February 2002).
'Our earthworks foreman on this job was actually on the first bypass project, so we have a good idea what the ground conditions are likely to be, ' says May Gurney projects manager Jeremy Sturla. 'So by getting involved at a much earlier stage than normal we were able to come up with better solutions for the earthworks problems and have been able to offer the client real value for money.' Early contractor involvement (ECI) meant that May Gurney, its designer FaberMaunsell, the Highways Agency, and the Agency's consultant Hyder were working as a team by February 2003, long before the final route was agreed.
Sturla says the team soon accepted that a public inquiry was almost inevitable. Despite its apparent simplicity the bypass contained a remarkable collection of potentially controversial features. Norfolk County Council (NCC) wanted a roundabout at the eastern end, for example.
But, as FaberMaunsell associate director Stephen Ellis says, 'The Agency's priority was to dual a trunk road, not provide local access.' He adds: 'This is a short length of bypass with four potential junctions serving a town of only 20,000 people. Each junction had to be looked at closely in terms of value for money.' By October 2003 alternative junction designs were published for public comment, and by March 2004 a 'fully agreed' solution was ready for public display. Sturla admits that 'it wasn't possible to satisfy everybody. There were still a couple of landowners north of the West Carr junction unhappy'.
NCC had accepted a solution at the eastern end which involved a redesign to the sliproads at the Queen's Road junction that would facilitate the future construction of a roundabout. Following the public inquiry in November 2004, only 1 0 months before work on site was due to start, design of the West Carr junction was modified to include an overbridge for pedestrians, cyclists and horse riders. 'We decided to make this a landmark structure, the 'gateway to Attleborough', ' Ellis says.
'It will be a 50m span tied arch painted bright red. A bowstring design would have been too obtrusive in a flat area, so the tied arch solution was more appropriate.' Solutions were also needed for the environmental challenges of diverting the Attleborough stream away from the line of the new carriageway through water vole breeding grounds. Work had to be programmed for late in the spring to prevent undue disturbance. Meanwhile, a sunny embankment constructed during the previous contract is popular with basking grass snakes and lizards. A capture programme had to be scheduled for October when cooler weather made the reptiles sluggish. Excavation could then proceed.
The team approached the public inquiry with confidence, Sturla says. 'It only lasted a week, and of the 10 original objectors only four turned up. 'In March this year we got the go-ahead. Then we could finalise the target cost and get ready for the start of advanced works in August.'
A key priority was to minimise noise and disruption when working close to housing. One of the three culverts on the Attleborough stream diversion is close to the hamlet of Baconsthorpe north of the Queen's Road junction and is crossed by a busy B road.
'We looked at the options of corrugated steel and precast concrete - and rejected them, ' says Sturla. 'For a start, precast units would have been pretty big, which would have meant large cranes and major disruption.
'So we decided that as we would have to sheet pile to allow the permanent works to be constructed, why not use the sheet piles as part of the permanent works-' The final design featured a simple insitu slab spanning between the sheet pile walls, with an oak plank otter pass bolted to brackets below. Sturla goes on: 'Major service diversions were also involved, with lots of traffic management.
'Noisy piling plus traffic management equals lots of unhappy local residents. So we decided to spend an extra £30,000 on silent hydraulic pull piling - money well spent in the long term.' Minimising noise, disruption and traffic management was also a factor in the design of the Queen's Road overbridge. An integral option was selected, featuring precast concrete beams topped by urethane foam fill (see diagram).
'This minimises the use of silane, which means less traffic management, ' Sturla explains.
'And, unlike some other options, there is no risk of grout leaks during deck pours, which inevitably lead to claims from motorists passing below.' Early involvement also allowed greater certainty on the earthworks, Sturla adds. With the quality of the excavated material not expected to be high and the possibility of some form of stabilisation or improvement having to be used, the earthworks were hard to programme and costs difficult to predict. The answer was to begin work on the cut before the end of 2004 and stockpile the 77,000m 3 of excavated material until the spring.
'After the excavation we would know how much material was re-usable and if it needed stabilisation, ' Sturla explains.
'This gives us more fl exibility and cost certainty.' Ellis estimates that 11 weeks has been saved by opting for fully flexible construction for the new carriageway. 'Fully flexible costs more than conventional composite construction, ' he adds. 'But the time saved in not having to wait while concrete cures more than makes up for the extra cost.' May Gurney will shift into top gear next spring, with completion scheduled for a year later, just four years from the first meeting of the project team. ECI, says Sturla, 'is best compared to how projects were run in the time of Brunel, with all the project managers in one team.
'It means the least possible time from getting the go ahead to start on site. It means designing things only once. Clients get value for money. This is the first ECI project in East Anglia and it's convinced me that this is the way ahead.'