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Wind farm requires major earthwork  

Credit:  By Lori Lovely, Construction Equipment Guide, www.cegltd.com ~~

Before the massive wind turbines could be erected at White Oak Wind Farm, in McLean County northwest of the Bloomington/Normal metropolitan area in Illinois, the groundwork had to be laid – literally.

Rachel Contracting, based in St. Michael, Minn., served as the subcontractor responsible for constructing access roads to each of the 100 turbines, excavating and backfilling the foundation for each turbine, installing crane pads, maintaining 30 mi. (48.3 km) of county roads providing access to the project, building paths to enable the huge cranes to move from one turbine site to another, creating a staging area for office trailers and equipment and material staging, and providing support for other contractors as needed. During a February 2011 blizzard, that need included clearing snow, but at other times involved dealing with drainage issues.

Renewable Energy

The new wind farm, owned by Inveneregy LLC, in Chicago, Ill., will provide energy to more than 40,000 homes in Illinois. The project consists of the installation of 100 1.5 MW wind turbines in a partnership with General Contractor Mortenson Construction’s Renewable Energy Group out of Minneapolis, Minn., one of the leaders in North American energy construction.

The project is a perfect fit for Rachel Contracting, originally a heavy construction contracting firm founded by Don Rachel in 2006. When the economic crisis struck in late 2007 and the housing bubble burst, company strategy initially focused on special projects that were more complicated and/or difficult, such as environmental cleanup and complex demolition jobs.

But when the construction market continued to decline, Rachel’s management turned to wind farm development.

The renewable energy market has been strong and continues to grow, as does Rachel’s business, which reached contract volume of $25 million last year. The civil construction contractor worked on its first wind farm project in 2008 and by the spring of 2011, was working on three separate projects. Rachel representatives say the company’s culture and capabilities are a good fit for wind farm work, with its emphasis on environmental stewardship, problem solving and fast-pace production.

Work on White Oak commenced in early August 2010 and is expected to wrap up in May 2011. As with the other projects, it required a fast-paced schedule. Planning only began late in 2009, said Dave Lyste, renewable energy group manager of Rachel Contracting, and the project wasn’t approved until shortly before work began last summer.

“We were notified on August 2nd,” he said, “and we were on site with 10 pieces of equipment on August 5th.”

What It Takes

to Get the Job Done

The equipment list – most of it rented locally – includes three 84 in. (213.3 cm) smooth drum compactors, three 84 in. pad foot compactors, four 247/277/279 skid steer loaders, one 924 wheel loader, four 140 motorgraders, five D6 dozers, two 345 excavators, two 330 or 336 excavators, one 420 tractor-backhoe, a self-propelled broom with blade, two 4,000-gal. water trucks and miscellaneous small equipment and vehicles, as well as miscellaneous equipment required for the proprietary subgrade improvement work (milling machine, cement spreading trucks, etc.).

Because of the distance from headquarters, Lyste said only three or four pieces of equipment were taken from Rachel’s fleet to the job site; the rest was rented locally because it’s more cost-efficient. The 30-piece fleet of dozers, graders, excavators, compactors and skid steer loaders assembled at White Oak Wind Farm was collected from three different Illinois Cat dealers.

Practically the same could be said for the workforce.

“We only take a certain number of full-time employees, and supplement with local labor,” Lyste said, adding that finding good local labor is one of the challenges they face on jobs – particularly because as a union contractor, they rely on local divisions to supply the labor force.

Fortunately, he added, “we had a lot of good people on this job. The proximity of this site to Bloomington helped with the labor pool.”

At peak, Rachel had between 30 and 40 workers onsite, with an average of 15 at any given time. Overall, including all subs, the project averaged more than 100 workers onsite, with a peak at 190, for an approximate total of 50,000 man hours.

“There was a 7-acre parking lot for employees,” Lyste laughed.

There was another crowded area for materials. A staging area was set up for the 250,000 cu. yds. (191,139 cu m) of soil needed for the turbine foundations and the 120,000 tons (108,862 t) of aggregate base used on the roads.

“We set aside a stockpile, separating the topsoil from the clay to be used as backfill,” Lyste said. Sand was imported for soil correction for the subgrade in about a dozen areas where the foundation soil was soft or poor.

Paving the Way for Wind Towers

The job site spans an area approximately 6 by 30 square mi. (16,000 acres) on farmland owned by roughly 50 different people, who granted a 30-year land lease for the turbines and received extra payment for the access roads. One hundred 1.5 MW GE energy turbines were erected on the project site.

Each turbine sits on a 60 by 60 ft. (18.3 by 18.3 m) foundation “box,” as Rachel’s project superintendent Troy Baer describes them, that range from 7.5 to 10 ft. (2.3 to 3 m) deep, depending on the turbine. Rachel’s crews excavated the foundations, after which another contractor poured concrete – more than 300 cu. yds. (229.3 cu m) for each installation – and placed rebar and wired the site to the grounding grid. Rachel then backfilled and finished the site with surface rock.

Some of the foundations required soil stabilization to correct problem soils, as determined by pre-excavation coring samples or simple observation after excavation.

Local contractor Rock Solid Stabilization & Reclamation, based in Ringwood, Ill., performed the soil stabilization work.

Stabilization of the existing subgrade also was required for some of the 26 mi. (41.8 km) of 15-ft. (4.6 m) -wide site access roads. Post-construction traffic is minimal on the permanent roads, but the weight load is heavy. Rachel implemented a proprietary design by mixing cement into the soil to improve and stabilize the subgrade. In formulating the design to create long-lasting roads, they evaluated the layout, soil type and condition, using a reclaiming machine for the cement stabilization. Lyste said the process has worked well on other sites, but he prefers to keep details secret because “not everyone is using this method.”

Leveling the Playing Field

Explaining that a 150-ft. (45.7 m) radius around the turbines is required, Lyste said grading work was necessary to meet job specifications.

“There were limitations about the type of grade,” he said. A 1 percent side-to-side grade necessitated crews cut the side of the hill so the travel path was flat for the cranes to reach the location for tower installation. The allowable grade front-to-back was 8 to 10 percent.

Although the central Illinois area is relatively flat, Lyste said the farmland covers “some rolling hills,” making drainage an issue. At White Oak, Rachel installed more than 10,000 linear ft. (3,048 m) of corrugated metal pipe culverts at the site road entrances and at locations where the site roads crossed existing water crossings to preserve, and in some cases, enhance natural drainage.

“Drainage can’t be affected by construction,” Lyste said. “Officially, this was a design-build project, but as with all field construction, you have to ‘wing it’ when you encounter things.”

One of the spontaneous judgment calls was to reroute existing waterways when they affected travel, although Lyste said they extended every effort not to alter the contour of the farmland. To ensure that the work they did had minimal impact on the land, they installed temporary erosion control, such as silt fencing.

In a further attempt to leave a light footprint, Lyste said wooden mats were used for a “soft road” when the cranes were moved into position. As they cut through the fields, Rachel’s equipment led the way, exposing potentially hazardous low spots and waterways, and removing snow when necessary.

“We had D6 dozers out in front of the cranes,” he recalled. Because work started at harvest time last year, they had to clear crops along the pathway because some of the corn was 8 ft. high. “We couldn’t see.”

Wind, Weather and

Watching the Clock

Because it’s a privately owned project, the budget has not been disclosed for public knowledge. White Oak was a typical project, Lyste believed, adding that it was a little more convenient than most because of its proximity to the city.

However, most projects don’t work through winter, but because of the schedule, “there was no downtime for this one.” The rush was somewhat related to the farmers’ planting schedule, Lyste said, but had more to do with money: the sooner the turbines began working, the better.

When Rachel’s crews started work last August, conditions were great, Lyste said, but a February blizzard threatened their schedule. The storms added to the workload, as snow removal was Rachel’s responsibility. Crews worked 12-hour days, six days a week to stay on schedule.

With soil that is “100 percent clay” and very difficult to work with – especially after a rain – there will be considerable restoration to complete.

“We built large radii for the big trucks to enter the job site, then spread topsoil. We have to put rock on the road to freshen it, and do some seeding,” said Lyste.

Source:  By Lori Lovely, Construction Equipment Guide, www.cegltd.com

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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