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The great M60 challenge

ROADS AND BRIDGES

As the main motorway serving Manchester it is crucial that traffic flow on the already congested M60 is improved to meet future needs.The widening of the road to achieve this presented the Highways Agency and contractors Alfred McAlpine and Amec with interesting challenges.

Alasdair Reisner visited the site to see what progress is being made

CONSTRUCTION NEWS is inclined to ask Graham Dakin to pull the other one.Mr Dakin is the Highways Agency's project leader for the M60 widening project in Manchester. So far, so good. But things get slightly less credible when he says that this mammoth £102 million feat of civil engineering will actually improve the environment for those living nearby.

Over here Graham, this one's got bells on it.

But Mr Dakin is no fantasist. By the time the scheme, being built by an Amec/Alfred McAlpine joint venture, is completed in spring 2006 there should be a genuine improvement in the impact of the motorway on both the natural and built environment it runs through.Although the use of landscaping, noise barriers and the lowering of the carriageway won't completely remove the effects on its surroundings, those living along the route will welcome any improvement these bring.

But why bother with widening the road at all? The answer to that can be seen any morning or evening when it snarls up with commuters coming in to and out of the city. Put simply, the M60 is bursting at the seams.The team has been tasked with letting out these seams; loosening the belt that is cutting off the city's circulation.

The project team is widening one of the worst affected sections, to the south-west of the city centre.But space is at a premium, with the road threading its way between the housing along both sides, the rail, tram and canal routes that serve the city, the River Mersey and the locally renowned Sale Water Park.

Robert Coupe, Alfred McAlpine's construction director for civil engineering, who is working on the joint venture, says: 'The job is certainly complex.We're not just putting a new lane on either side of the road.The land available moves from side to side along the route and this is often at different levels to the current road surface.This makes keeping lanes open during the work very complicated.'

But because of the congestion, neither the Highways Agency nor the travelling public would accept having lanes closed.The need to keep the road at full capacity during peak hours has been written into the team's contract.

'We are keeping the same number of lanes open at peak times as there are now, ' says Mr Dakin.'Where there are three lanes open now there will be three lanes open at peak times throughout the works.'

That's all fine, but with a job like this, which is a major earthmoving operation, bringing in 1.5 million tonnes of bulk fill material while constructing a new carriageway alongside the existing road hasn't made things easy. Fortunately the team had planned ahead for this issue.

While the contract is expected to last for 156 weeks, the joint venture took the first 20 weeks to work on the designs for the project.After this, the team moved on to site, but working away from the line of the road. It was during this time that much of the material needed to build the scheme was brought on site, reducing the disruption caused by wagons delivering to the site.

The bulk fill material is needed because the current motorway is built on embankments over the Mersey Valley.The imported material will raise the surrounding ground to the same level. But the limited land availability around the road means the team has had to come up with space-saving solutions.

'There are a number of reinforced earth walls and embankments to allow us to remain within the land take for the scheme, ' says Mr Coupe.'An embankment with a gradient of one-in-three would come out too far away from the line of the road and we'd have needed a concrete retaining wall. But by steepening up the embankments using a number of options, such as precast concrete panels with straps on and geotextile reinforcement, we have engineered out the need for retaining walls.'

But the team also had to deal with less-than-ideal ground conditions across much of the site, as Mr Dakin explains: 'There are approximately 14 former landfill sites along the route of the widening, dating from the early1900s to the mid-1990s.The refuse in them ranges from domestic waste to ash and glass.'

Much of the route of the widening is also founded on soft alluvial material and up to six different treatments were used to counter the instability in the ground.

'We've used vertical concrete columns, vertical stone columns, continuous flight augur piles, band drains and some dig-out and recompact, ' says Mr Coupe.

Where the ground beneath some sections wasn't strong enough to support conventional fill, large polystyrene blocks - an increasingly popular solution - were used.

'We dug out 2 m from the existing embankment, ' explains Mr Coupe.

'The average weight of earth is two tonnes per cubic metre, so if you go down 2 m you get four tonnes of load. If you put 10 m of polystyrene on top of that, which might have a dead weight of four tonnes, the actual load will be the same.'

With the strict programming of the job, it's vital that there are no delays.

One could have occurred when a section of the polystyrene was targeted by vandals in the summer - but elsewhere on site the team has looked at areas where time savings can be made, giving them a level of comfort in meeting their deadlines.

'The programme dictated that the earthworks operation had to continue throughout the whole 12 months of the year, ' says Mr Dakin.This is unusual for earthworks operations as weather conditions over the winter can leave sites in a quagmire as soil turns to mud.

'To ensure that we met our programme we went for class one imported shale, ' he explains.

'The cheapest material would have been clay but if it's raining, clay can't be placed; the general rule is that clay can't be placed for the six weeks before Christmas and 12 weeks afterwards.'

Now, at the half-way stage, the team is currently on target to deliver the project on time and to the required environmental specifications in spring 2006 - giving Mr Dakin's claims, as unlikely as they first appeared, a ring of truth after all.

Gone in 60 seconds

ONE OF the most challenging and exciting parts of the M60 widening project took place last month as 1,000 tonnes of existing bridgework toppled to the ground in a single controlled explosive demolition.

The bridge was first weakened along its 78 m span before a 200 m exclusion zone was established. In order for the bridge to be safely demolished, the section of the M60 surrounding the bridge was closed.

Project details

Client: Highways Agency

Contractor: Amec/Alfred McAlpine joint venture

Client's agent: Mouchel Parkman

Designers: Halcrow

Value: £102 million

Contract length: 156 weeks