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Around the houses

Construction of a new road is a rare sight across the UK. Environmental concerns, efforts to increase use of public transport as well as cuts in government funding have all significantly reduced the number of new road building projects in recent years.

But there are plenty of bottlenecks across the road network and new capacity can lead to local regeneration. Construction of the 6.5km dual carriageway Corby bypass is one such scheme.

“The A43 Corby Link Road is a major highway scheme that has been developed over many years by the county council and remains a high priority with the aim of improving transport links between Corby and the A14,” says client Northamptonshire County Council leader Jim Harker.

Corby

On line connection: Construction is focused around the southern end of the route, where the new road leaves the existing highway network at the A6003 and where Interserve is constructing a new roundabout.

“It will also help to facilitate economic and population growth in the north of the county, in and around Corby and will relieve the A43 at Geddington of through traffic.”

The new road is a 6.5km dual carriageway linking development areas to the east of Corby with the A14 via the A6003 while at the same time providing relief for the village Geddington.

“It will help to facilitate economic and population growth in the north of the county and around Corby”

Jim Harker, Northamptonshire County Council

“The people of Geddington have been campaigning for a bypass for over 40 years and will be enormously relieved that it is, at last, about to happen,” adds Harker.

Main contractor Interserve is building the new route.

It will run roughly south west to north east, leaving the A6003 just north of Kettering and following the Kettering-Manton railway line across farmland before joining the A43 at Stanion.

In the process it will provide a diversion for the single carriageway A43 around the bottleneck at Geddington.

“It has poor visibility and is prone to flooding,” says Interserve project manager Andy Bond. “It is a major route but with very old specifications.”

Harpers Brook

Big pour: Foundations for Harpers Brook culvert underway

Site preparation work is underway, with the main contract due to start in July. Completion is expected in early 2014.

Plans for the Corby bypass were first mooted in the early 1980s, according to Bond. It was originally envisaged as a Department for Transport/Highways Agency project with development work done in the 1980s and 1990s. But the project never reached the construction phase.

The A43 section close to Corby was de-trunked in 2001 and transferred to Northamptonshire County Council which reinvigorated plans for the scheme.

Plans were worked up by the council early in the last decade with a successful public enquiry taking place in 2008.

A best and final bid was submitted in 2011 with the Department for Transport (DfT) approving £20M of the scheme’s £34M cost in May last year. Funds from Section 106 agreements make up the rest of the funding.

“It’s been a long time coming” says Bond.

Tenders for the project were announced in late 2011, with Interserve securing the main contract at the end of May 2012 and starting on site in early June. Consultant Atkins had already completed much of the design work before the funds were secured, according to Bond, so there was no need for an early contractor involvement arrangement.

“There has been a move away from bridges with expansion joints as water tends to leak down”

Spencer Banks, RMD

“At least on day one you know more or less what the project is,” says Bond.

Construction is currently focused around the southern end of the route, where the new road leaves the existing highway network at the A6003 and where Interserve is constructing a new roundabout. Although the majority of the roundabout work is offline, it will impact on the A6003 when the tie ins are constructed.

“It’s being built half online and half offline but we have to maintain use of the existing road,” says Bond.

The route then veers northeasterly through farmland, cutting across two existing roads and a farm track; this requires the construction of three bridges. The north east end of the route is hillier, and requires cuttings of up to 14m deep. The new road re-joins the existing road network at the A43 junction at Stanion where the existing roundabout will be increased in capacity.

SAM_0473

Earthworks form the largest part of the project, according to Bond, as over 1.5M.m3 of material must be moved. The site is virtually all class two stiff clay.

“It’s difficult to work with,” says Bond “And [the earthworks programme] is on the critical path.”

Fortunately this year’s unending winter has not affected the overall timetable, as most of the work not due to get underway until now.

But Bond is trying to keep ahead of schedule, and 30,000m3 of soil was moved in February. The firm is reusing the fill for embankments or landscaping on other areas of the route.

Interserve is also building three main bridges over the route - Little Oakley and Newton Road bridges are 60m long - which serve to maintain public highways severed by the route - and Featherbed bridge is 54m long - which provides farm access.

In the tender documents, the bridges design consisted of a three span precast concrete structure.

But there was a 1.5m gap between the pier head and the precast main beam for the road deck of 1.5m requiring temporary formwork for an in-situ pour to fill the gap, according to RMD engineering manager Spencer Banks.

“[Constructing this design] would have required heavy duty scaffolding,” says Banks.

As a result during the value engineering exercise, Interserve altered the detail to remove the in-situ pour.

Interserve has just begun clearing the site to construct the three bridges.

Each bridge sits on nine 600mm diameter 17.5m deep CFA piles on the two bank seats and 14, 600mm diameter, CFA piles 9.5m deep at the piers.

The bridges are fully integral so there is no expansion joint at the piers or embankments to accommodate movement from thermal expansion.

“There has been a move away from bridges with expansion joints as water tends to leak down causing corrosion of the bearings below,” explains Banks.

To accommodate thermal expansion, the bank seats are designed to move. Over each pile cap, engineers are installing a 2.5m long 850mm wide steel sleeve. This will sit within the pile cap and allow a 60mm lateral movement.

Along with the three main bridges, Interserve is building a large 2m wide culvert above Harpers Brook about 4.3km from the southern end.

This part of the route lies on a flood plain, and construction includes building a flood alleviation area. Along with the culvert, Interserve is building six 2.9m diameter corrugated steel flood arches to allow water to flow underneath the road in a 1 in 100 year flood.

Environmental requirements for the project are strict, according to Bond. He has employed an ecological clerk of works to ensure all the standards are being met.

Bridge construction is due to be finish by September and the subbase of the main alignment due to be completed by October.

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