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Connect goes into orbit

ROADS AND BRIDGES

A challenging road job in Scotland is proving no problem for Connect, as Alasdair Reisner discovers

'WE KNOW when we are going to be finished. Spring 2005. I think it is the most certain thing in the world. I've told people to go to the bookies and put a bet on it. It's a cert.'

You certainly cannot accuse Iain Mackay of a lack of confidence.As manager of Connect's £130 million M77/Glasgow Southern Orbital he is in charge of Scotland's largest single road building project in recent years, yet this does not seem to have instilled any sense of fear in him.

Perhaps this is because his confidence is backed up by solid performance.The team, led by Balfour Beatty and Atkins, is more than halfway through the two-year construction period for the contract and is still charging ahead with the works.

As its name indicates, the project in fact consists of two distinct parts:

the upgrade of the existing A77 to dual two-lane motorway standard over 15 km, and a brand new 9.2 km two-lane dual carriageway bypass of the town of Eaglesham, known as the Glasgow Southern Orbital.

Indeed the job was originally proposed as two separate schemes, promoted by the Scottish Executive and East Renfrewshire Council respectively. But there was a requirement for a major interchange between the two roads at Maidenhill.

'At that point it made sense to join the two schemes together but then it became a large project.They looked at the way to design and construct it and this Private Finance Initiative solution came out as the best, ' says Mr Mackay.

The scheme was officially awarded to Connect at the end of April last year but by then the team had already had five months work on the job under its belts.How can this be?

'We had been made preferred bidder in early November 2002. It was evident that if you only commenced the design after financial close, delivering the scheme in 24 months would have been virtually impossible.

A decision was taken to start design work straight away, ' says Mr Mackay.

There is always a very slight risk that the team's preferred bidder status would not be converted into a contract on paper but by taking this decision Connect was ready to meet the challenges facing it on the job straight after the deal was signed.

Perhaps the greatest of these is found in the scenery that the planned route of the road drives through.

While the rolling hills may make for pleasant viewing as you drive between Glasgow and Kilmarnock, they present a major challenge if you are trying to build a major road through them, forming cuttings and embankments as you go.

'In terms of earthworks volumes we are talking about 3 million cu m in total, a lot of which is through peat, so it is a difficult job, ' says Mike Dobbs, Balfour Beatty Civil Engineering's project manager for earthworks.

n See page 46 The peat presents a problem as in places it is little more than slop.Not ideal when trying to build an embankment on top of it.

'It's was a big challenge to limit the amount we had to dig out and replace.We've got embankments that are about 10 m high.They are formed on top of peat deposits that have to be removed because of the long-term settlement characteristics. Below is about 4 m of soft alluvial clay and silt, which we have tried to leave in place, ' says Mr Dobbs.

But in doing this it was vital to avoid deep-seated failures in the ground below the road.A nightmare scenario like this could have set the team back weeks and required remedial action, something that could not be afforded under the contract.

'At the end of the day we went for a staged embankment construction with strengthening geotextile in the starter layer. It is a very strong tensilebased geotextile that prevents these deep-seated failure planes by forming an anchor.When a failure starts, the anchor layer will hold it and prevent that from happening, ' says Mr Dobbs.

The embankments are built up in 3 m layers. Each is left to consolidate and increase in sheer strength before another layer is added - up to a maximum of 12 m - on the site.The possibility of failure during this process is mediated by the use of mass pedometers, which measure the ground water pressure in the soil. If it rises too high and there is a risk of failure, work could be stopped to allow the ground more time to consolidate.

But where did the material required for building these embankments come from? Essentially the team was expected to carry out the earthworks on the scheme without disposal or import of material.Where embankments had to be built they were done so with material taken from elsewhere on site.Given that a lot of this material was very moist and not ideal for construction, how did they get round this problem?

'On the GSO there was a shortfall of material.We had about 330,000 cu m of acceptable type and 330,000 of class four unacceptable material.Our strategy was to modify that material by adding lime to bring the moisture correction value to a usable level, ' says Iain Mackay.

The team also benefited from long periods of fine weather during the contract, allowing some of the material to be air dried, increasing its suitability.Once this process was completed the material could be used as fill for embankments.

While this was going on the team was also working with utility companies in order to secure diversions of services across the site wherever they were needed.

Mr Welsh admits that this can often be a headache during road building projects as the demands of the team to meet the programme often does not tally with that of the utility companies, who are in no rush. So something he is particularly pleased with is that all of the diversions on the M77/GSO project have been arranged without a hitch.

'Not many projects can say that.We had seven major gas diversions and because they are carried out by the gas company, not us, we could have lost some control. But all of the utilities have been broadly co-operative and have worked with us rather than against us, ' says Mr Welsh.

With surfacing work on the project now ploughing ahead, the job is on target for completion as scheduled in April 2005.

So, if you want to get down the bookies and follow Mr Mackay's tip, you don't have much time left.

Having a blast CLOSE to a live gas main? Just a stone's throw away from the busy A77?

Surely this was one job where the project team could not get away with blasting its way through the scenery to make way for the new road.

According to David Welsh, such constraints were not a problem.

'We were blasting to gain high-quality rock for the scheme.Within the M77 we had five rock cuttings, four of which were alongside the existing A77 - as close as 70 m, ' says Mr Dobbs.

Yet by working with the police the team came up with a solution that meant the blasting could be completed with a barely noticeable effect on the running of the road.The explosives experts who carried out the job used a slurry explosive, which can be easily controlled, following trial blasts to determine velocity and shock waves associated with blasting in the area.

'We used a rolling block system on the road.We got it quite slick, down to six minutes to put the block on, carry out the blasting, check the road for debris, sound the all-clear and re-open the road, ' says Mr Dobbs.

Project details

Client: East Renfrewshire Council (lead), South Lanarkshire Council, Scottish Executive

Project consortium: Connect (Balfour Beatty/Atkins)

Main contractor: Balfour Beatty Civil Engineering

Lead designer: Atkins Sub-designers: Scott Wilson/Ironside Farrar

Earthworks: VHE

Value: £130 million

Design and construct period: Two years