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Earth Wind and Concrete

Earth, Wind and Concrete

With around 90 wind farms currently under construction in the UK, developers are taking full advantage of the UK’s enviable claim to fame as the windiest region in Europe. But although wind is free, much capital investment is needed at the outset. This, combined with often isolated locations, harsh terrain and other environmental constraints, can lead to quite challenging construction schedules.

At Carraig Gheal Wind Farm in Scotland, contracting specialist Blackwell has nevertheless shown how careful planning and technical ingenuity can more than cope with these demands.

Carraig Gheal Wind Farm is, by most people’s standards, remote, only 21 miles from the west-coast resort town of Oban in the Argyll and Bute region of Scotland, and just 100 miles north of Glasgow, it is nevertheless not an easy place to get to by road.

And then there is the site itself. Around 1,200 hectares in size and rising to about 450 metres above sea level, the Carraig Gheal site was essentially a hilly Highland wilderness, inaccessible to most, and just the occasional narrow dirt track, furrowed over generations by the local foresters and farmers.

That was still the case in early spring 2012. Yet in just a few months, Blackwell has impressively created more than 45km of robust roadway through the site. Almost 10km of this provides access to the 20 wind turbine sites, while the remainder has been constructed through the site to aid the local forestry industry and help remove traffic from the local country lanes. On top of this, Blackwell has constructed 76,850 sq metres of hard-standing area.

David McCracken, Project Manager for Blackwell on the Carraig Gheal site, said: “Whichever way you look at it, that’s pretty good going. We’ve turned that aspect of the job round very quickly, and that’s only a small part of what we’ve had to do.”

Much of the urgency was the result of factors outside Blackwell’s control. The company was appointed as the main contractor by Green Power, a private enterprise firm, as recently as Christmas Eve 2011.

The original winning contractor started work in 2011 but pulled out, leaving Blackwell to step in at the eleventh hour and pick up the pieces. By Christmas 2011, the Scottish winter was making its presence felt.

“We suffered a terrible winter initially,” said McCracken. “It was pretty disastrous in terms of getting work done. It’s already a rough environment, but when you add a lot of wind, rain and snow, and the fact it gets dark very early, means the schedule was looking quite scary.”

Fortunes turned around though, and road construction began in February this year – and continued at a startling pace.

McCracken said: “Since March, we’ve actually been reasonably lucky with the weather. This part of Scotland has been drier than usual through the spring and summer, and certainly drier than most of the UK.”

Rob King, resource manager for Blackwell, nevertheless admitted that, even with a good spell of weather, the environmental conditions have remained extremely challenging, and the project would not have run on time and on budget without its fleet of 30-tonne B30D ADTs from Bell Equipment, plus an impressive piece of technical innovation along the way.

In addition to problems created by the terrain and the weather, the project has also had to deal with numerous ecological constraints, some of which have either increased the workload or delayed the schedule, or both. Blackwell has employed its own ecologist throughout the project to work with the client’s own ecological team and generate solutions to the inevitable wildlife protection issues.

Nesting ospreys, golden eagles and red-throated divers have required very careful consideration and protection – sometimes to a point where work has had to stop completely on parts of the site.

King said that, when sections of road had, for example, been made impassable due to nesting birds, it was essential to retain the flexibility of access to parts of the site using un-treated cross-country routes, which 4x4 vehicles, let alone normal road-going lorries would largely find it impossible to cope with.

“This is why we were always going to use articulated dump trucks,” he said. “There was never any other vehicle that was going to move the materials in the conditions we had. And the Bell trucks are extremely manoeuvrable.”

It is for that reason alone, he said, that Blackwell decided to work with Bell to find a way of turning its classic ADT into an off-road concrete mixer.

The Bell ADT concrete mixers had been recently developed and trialled on the massive Clyde Wind Farm project, and had proven highly successful. So Blackwell commissioned a total of five converted Bell trucks.

Working in tandem with a concrete mixer specialist in Buckingham, Utranazz group, a specially designed sub-frame was manufactured which would allow Blackwell to mount a self-contained, self-powered mixer unit onto the dump truck chassis.

“We tweaked a few elements here and there, like repositioning radiators, installing new dampers and improving some brackets. We wanted the mixer unit to be completely independent from the existing electronics within the truck, so that we could retain the flexibility to convert it back to a standard haul truck.” said King.

He said that other operators had attempted similar conversions previously, but only in a “very crude roll-on, roll-off skip lorry” manner. This was the first time that a fully functioning concrete mixer had been created using an ADT chassis, which could also be easily converted back to a basic ADT.

King said: “The configuration of the design following this co-operation with Bell and the mixer specialist means we can convert the truck back for normal use in less than four hours. This flexibility not only means our trucks can be utilised even when batching and pouring isn’t taking place, but it also gives us flexibility with our drivers. This can be very useful at a remote site like Carraig Gheal, where labour is not always easy to source.”

Each of the 20 turbines at Carraig Gheal stands in a base of about 330 cubic metres of concrete and about 45 tonnes of steel.

Due to the sheer volume of concrete, Blackwell built its own batching plant on site. Without this facility, it would have been impossible to meet the schedule, not least because standard concrete mixers would not have been able to access places that the ADTs could.

King said: “We’d have had to be much more critical with the roads if we’d attempted to use normal concrete mixers. We simply wouldn’t have had the time for that on our already very tight work schedule. The Bells have no problem coping – and don’t create anywhere near the amount of downtime we might have faced with other methods of transport in these difficult ground conditions.”

When the main thrust of the road infrastructure programme was underway, Blackwell had around 30 Bell ADTs on site, hauling rock and peat on steep and difficult terrain, working alongside dozers and excavators.

The 20 turbine sites are dotted across the central section of the site, 500 metres apart to avoid “wind shadow”. Each turbine site is initially excavated and a platform of about three or four inches of concrete is prepared to provide a flat working base. A mass of steel rebar is installed to provide the necessary reinforcement before the “pour” takes place. From start to finish, each turbine base takes on average three weeks.

Within a few months of work, not only the roads had to be completed, but the bases had to be ready in time for the delivery and installation of the first turbines in early September 2012. There was also more than 11km of cabling track to lay to connect each turbine – typically along the route of the roads, but sometimes across country.

Siemens has been responsible for installation of its 2.3MW turbines – the logistics of which have left no room for unscheduled on-site delays.

Blackwell’s initial handover date is December 18, 2012, meaning the installation schedule has run to about two turbines per week. The final handover will be in March 2013, though the bulk of the work will have been completed this year.

Carraig Gheal Wind Farm will thus join the other 350 onshore wind farms already operating in the UK and will contribute to the ongoing drive for renewable energy by powering the equivalent of more than 25,000 homes.

The renewable energy story does not end there though. There are currently around 90 wind farms of varying sizes that are currently under construction in the UK – of which 36 are in Scotland. More than 600 additional projects are either approved and not yet under construction, or are still in the planning process.

The Scottish Government alone has a target of generating 100 per cent of the country’s electricity from renewable energy by 2020, the majority of which is likely to come from wind power.

Given the enormity of the ambition, South African manufacturer Bell Equipment believes that Blackwell has helped unveil a perfect solution for concrete handling to the wind farm industry – one which will genuinely improve the chances of projects getting completed on time and on budget, as has been proven at Carraig Gheal.

Simon Bridge, regional sales manager for Bell Equipment UK, said: “The flexibility of the Bell ADTs cannot be underestimated. Blackwell has recognised this, not only in using its Bell fleet for normal haul duties in these very challenging conditions, but in going one stage further by using them as concrete mixers.

“It’s a truly innovative use of an ADT. Bell is no stranger to manufacturing bespoke ADTs for our customers for a wide variety of applications, though we could feasibly see this concrete mixer hybrid ADT as a popular addition to our ADT range in its own right.”

Bell’s B30D ADT is powered by a six cylinder turbo-charged Mercedes engine, providing 240kW of gross power and 1,250Nm of gross torque. Alongside Bell’s other ADTs, it is also the most fuel-efficient ADT of its size on the market, which Bridge said created an even greater incentive for developers and proponents of renewable energy.

Recent independent tests run on simulated quarry conditions at Millbrook Proving Ground, in Bedfordshire, showed that the Bell B30D truck was 17.6% more fuel efficient than the equivalent model from a market leading rival manufacturer.

Bridge said: “It has been stated that the average wind farm in the UK will pay back the energy used to build it within six or eight months. It must therefore follow that, if you can reduce than energy consumption by being more fuel efficient and speeding up the build, then the pay back will happen sooner.”

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